TypeORM - Introduction

TypeORM framework is an Object Relational Mapping (ORM) framework. In general, Object part refers to the domain / model in your apppcation, Relational part refers to the relationship between tables in Relational Database Management System (e.g. Oracle, MySQL, MS-SQL, PostgreSQL, etc.) and finally the Mapping part refers to the act of bridging the model and our tables.

ORM is a type of tool that maps entities with database tables. ORM provides simppfied development process by automating object-to-table and table-to-object conversion. Once you can write your data model in one place, it becomes easier to update, maintain, and reuse the code.

Since, the model is weakly bound to the rest of the apppcation, you can change it without any hard dependency with other part of the apppcation and can be easily use it anywhere inside the apppcation. TypeORM is very flexible, abstracts the DB system away from the apppcation and allows us to benefits from the use of OOPS concept.

Overview

TypeORM is an Object Relational Mapper pbrary running in node.js and written in TypeScript. TypeScript is an improvement to JavaScript with optional typing. TypeScript is a compiled language. It is not interpreted at run-time. The TypeScript compiler takes TypeScript files (.ts) and compiles them in to JavaScript files (.js).

TypeORM supports multiple databases pke MySQL, PostgreSQL, MariaDB, SQLite, MS SQL Server, Oracle, SAP Hana and WebSQL. TypeORM is an easy-to-use ORM to scaffold new apps that connect to databases. TypeORM functionapty is RDBMS-specific concepts.

We can quickly create new projects and micro-services. It is inspired from similar tool pke Hibernate, Doctrine, Entity framework, etc., from other programming languages.

Features of TypeORM

TypeORM comes with the following features −

Automatically create database table schemes based on your models.

Easily insert, update and delete object in the database.

Create mapping (one-to-one, one-to-many and many-to-many) between tables.

Provides simple CLI commands.

Benefits of TypeORM

TypeORM is easy to use ORM framework with simple coding. It has the following benefits −

High quapty and loosely-coupled apppcations.

Scalable apppcations.

Easily integrate with other modules.

Perfectly fits any architecture from small to enterprise apps.

TypeORM - Installation

This chapter explains about how to install TypeORM on your machine. Before moving to installation, please make sure that npm is installed. To confirm that you have npm, you can run the following command in your terminal.

npm -v

It shows the version. If it is not installed, download the latest version and install on your machine.

Install TypeORM

Let us install TypeORM locally using npm module −

npm install typeorm --save

After executing the above command, you will get a response as given below −

+ typeorm@0.2.24 
+ 
added 1 package and audited 1236 packages in 4.729s

Alternatively, to install TypeORM globally, use the below command −

npm install typeorm -g

After that, install optional package reflect-metadata using npm −

npm install reflect-metadata --save

You could see the following response −

+ reflect-metadata@0.1.13 

added 1 package and audited 1236 packages in 2.426s

Now, install another optional package. node typings using the below command −

npm install @types/node --save

You could see the following response −

+ @types/node@12.12.31 

added 1 package and audited 1236 packages in 2.167s

Install database driver

In this section, let us install the necessary node packages for our database.

To install MySQL or MariaDB package, use the below command −

npm install mysql --save

You could see the following response −

+ mysql@2.18.1 

added 1 package and audited 1236 packages in 4.36s

To install PostgreSQL package, use the below command −

npm install pg --save

You could see the following response −

+ pg@7.18.2 

added 1 package and audited 1236 packages in 2.863s

To install SQLite package, use the below command −

npm install sqpte3 --save

You could see the following response −

+ sqpte3@4.1.1 
added 48 packages from 45 contributors and audited 1396 packages in 7.31s

To install Microsoft SQL Server package, use the below command −

npm install mssql --save

Your screen looks similar to this,

+ mssql@6.2.0 

added 1 package and audited 1655 packages in 2.378s

To install sql.js package, use the below command −

npm install sql.js --save

You could see the following response −

+ sql.js@1.2.1 

added 1 package and audited 1655 packages in 6.462s

To install Oracle server package, use the below command −

npm install oracledb --save

You could see the following response −

+ oracledb@4.2.0 

added 1 package and audited 1655 packages in 2.265s

To install mongodb package, use the below command −

npm install mongodb --save

You could see the following response −

+ mongodb@3.5.5 

added 1 package and audited 1655 packages in 3.716s

TypeORM - Creating a Simple Project

This chapter explains about how to create simple TypeORM apppcation. Let us create a new directory named ‘TypeORM’ and move into the directory.

cd /path/to/TypeORM/

Syntax

Use below command to create new project −

typeorm init --name <project-name> --database <database-name>

Example

typeorm init --name FirstProject --database mysql

Here,

FirstProject is your project name and sqpte3 is database name. After executing the above command, you could see the following response,

Project created inside /path/to/TypeORM/FirstProject directory

Now, move in to our project directory and install project dependencies using npm module,

$ cd FirstProject 

$ npm install

Project structure

Let us understand project structure of our newly created project, FirstProject.

FirstProject 
├──> src 
│ ├──> entity 
│ │ └──> User.ts 
│ ├──> migration 
│ └──> index.ts 
├──> node_modules 
├──> ormconfig.json 
├──> package.json 
├──> package-lock.json 
└──> tsconfig.json

Here,

src − contains source code of your apppcation in TypeScript language. It has a file index.ts and two sub directories entity and migration.

index.ts − Your entry point to the apppcation.

entity − Contains database models.

migration − contains database migration code.

node_modules − locally saved npm modules.

ormconfig.json − Main configuration file of your apppcation. It contains database configuration details and entities configuration.

package.json − Contains node module dependencies.

package-lock.json − Auto generated file and related to package.json.

tsconfig.json − Contains TypeScript specific compiler options.

ormconfig.json file

Let us check the configuration option available for our apppcation. Open ormconfig.json file and it looks similar to this −

{ 
   "type": "mysql", 
   "host": "localhost", 
   "port": 3306, 
   "username": "test", 
   "password": "test", 
   "database": "test", 
   "synchronize": true, 
   "logging": false, 
   "entities": [ 
      "src/entity/**/*.ts" ], 
   "migrations": [ "src/migration/**/*.ts" 
   ], 
   "subscribers": [ "src/subscriber/**/*.ts" 
   ], 
   "cp": { 
      "entitiesDir":"src/entity", "migrationsDir":"src/migration", "subscribersDir":"src/subscriber
   }    
 }

Here,

type, host, username, password, database and port options are related to database setting. mysql can be configured using below configuration −

{ 
   "type": "mysql", 
   "host": "localhost", 
   "port": 3306, 
   "username": "db_username", "password": "db_password", "database": "db_name" 
}

entities − refers the location of your entity classes.

migrations − refers the location of your migration classes.

subscribers − refers the location of your subscriber classes.

cp − refers the option used by TypeORM CLI to auto generate the code

Start MySql server

Before starting the apppcation, start your MySQL server or any database server used by you and make sure it is running properly.

Run apppcation

Once everything is configured, we can execute the apppcation using the below command −

npm start

You could see the following response −

> FirstProject@0.0.1 start /Users/../../TypeORM/FirstProject 

> ts-node src/index.ts 

Inserting a new user into the database... Saved a new user with id: 1 Loading users from the database... Loaded users: [ User { id: 1, firstName:  Timber , lastName:  Saw , age: 25 }] 

Here you can setup and run express/koa/any other framework.

The apppcation inserted a new user into the database and then reverse load it from the database and finally show the loaded user in the console. We have successfully created a new TypeORM apppcation, configured it and run the apppcation.

We will discuss about how the data is executed elaborately in upcoming chapters.

TypeORM - Connection API

To interact with database, we need a connection object to the database. We need to create a connection object before doing the database operation and has to terminate it once thee database operations are done. Let us learn about Connection API provided by TypeORM in this section.

Creating a new connection

Before creating a new connection, we need to configure database connection details in the ormconfig.json configuration file. A sample connection details is shown below −

ormconfig.json

{ 
   name: "firstconnection", 
   type: "mysql", 
   host: "localhost", 
   port: 3306, 
   username: "root", 
   password: "root", 
   database: "firstDB" 
}

Here,

name − Name of the database connection.

type − Database type.

host − Hostname of the database server.

port − Database server port.

username − Account name having access to the database.

password − Password of the above mentioned account.

database − Name of the database to connect.

createConnection

CreateConnection method is provided by TypeORM to create a new connection. It is defined as below,

import { createConnection, Connection } from "typeorm"; 

const connection = await createConnection({ 

});

Here, createConnection will use the configuration details specified in the ormconfig.json file.

Alternatively, you can define the connection URL as arguments to the createConnection method as specified follows −

const connection = createConnection({ type:  mysql , 
     url:  localhost:8888/firstDB  
})

Here,

createConnection returns an object, which can be used to open / close the connection to the database.

Multiple connections

TypeORM provides an option to create multiple database connection as well. First, the configuration file ormconfig.json can be used to specify the details of the multiple database connection. Let us configure multiple databases in ormconfig.json as specified follows,

ormconfig.json

{  name: "firstconnection", 
   type: "mysql", 
   host: "localhost", 
   port: 3306, 
   username: "root", 
   password: "root", 
   database: "firstDB" 
}, 
{  name: "secondconnection", 
   type: "mysql", 
   host: "localhost", 
   port: 3306, 
   username: "root", 
   password: "root", 
   database: "secondDB" 
}, 
{  name: "thirdconnection", 
   type: "mysql", 
   host: "localhost", 
   port: 3306, 
   username: "root", 
   password: "root", 
   database: "thirdDB" 
}

Now, we can use the argument provided by the createConnection method to specify the name of the connection to create connection object as mentioned below −

const firstconnection: Connection = await createConnection("firstconnection");

Here,

createConnection will use the configuration details of the firstconnection specified in the ormconfig.json file to create the connection object.

TypeORM also provides yet another API, createConnections to create multiple connection as once and then, use it whenever necessary as specified below −

import { createConnections, Connection } from "typeorm"; 

const connections: Connection[] = await createConnections([ 

]);

Here,

connections hold all the connection objects as an array.

ConnectionManager

TypeORM also provides an another API, connectionManager to create connection. It is defined below −

import {getConnectionManager, ConnectionManager, Connection} from "typeorm"; 

const connectionManager = getConnectionManager(); 

const connection = connectionManager.create({ 

}); 
await connection.connect();

TypeORM prefers the usage of createConnection over ConnectionManager to create connection objects.

TypeORM - Entity

An entity is a collection of fields and associated database operations. It is used to map database table and its fields with the entities and its attributes. This chapter explains about the TypeORM entities in detail.

Introduction

Let us create a simple Entity class in our code. Move to your project root location and go inside src folder and move to entity folder. Now, create a TypeScript file, Student.ts and enter below code −

Student.ts

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; 

@Entity() 
export class Student {   

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   Name: string; 
   
   @Column() 
   age: number; 
}

Here,

Entity() decorator class is used to represent that the Student class is an entity.

PrimaryGeneratedColumn() decorator class is used to represent that the id column is the primary key column of the Student entity.

Column() decorator class is used to represent other columns such as Name and Age of the Student entity.

Now, Entity class Student is created. TypeORM will auto generate a table corresponding to the Student entity in our database and it will be named as student. Now, move to src/index.ts file and add the following code −

index.ts

import "reflect-metadata"; 
import {createConnection} from "typeorm";
import {Student} from "./entity/Student"; //import Student entity

createConnection().then(async connection => { 

   console.log("Inserting a new record into the student database..."); 
   
   //create student object const stud = new Student(); 
   
   //Assign student name and age here stud.Name = "student1"; 
   stud.age = 12; 
   
    //save student object in connection await connection.manager.save(stud); console.log("Saved a new user with id: " + stud.id);
    
    console.log("Loading users from the database...");

    //Display student saved records const students = await connection.manager.find(Student); console.log("Loaded users: ", students);

    console.log("Here you can setup and run express/koa/any other framework.");
}).catch(error => console.log(error));

Here,

Line 1 - 3 imports the relevant classes, createConnection and Student

Line 5 creates a new connection to the database using createConnection and if connection is estabpshed, it executes the code inside the then block.

Line 10 create new Student object, stud.

Line 13-14 set the attributes of our newly created stud object.

Line 17 saves the entity to the database using save method available in connection.manager object.

Line 23 fetches the student details from the database using find method available in connection.manager object.

Start Mysql server and run your apppcation

We have created Student entity and create connection in index.ts. Let us start both MySql server and your apppcation.

npm start

This will return the following output on your screen −

Output

Open mysql server following student table is added inside your database.

Columns

As learned earper, Entity is actually a collection of attributes. As entity object refers the database table. Its attributes / member variables refer the corresponding database table’s fields / columns. TypeORM supports all type of database fields through Column class. Let us learn the different type of column supported by TypeORM in this chapter.

@Column() decorator class is used to represent the column and its type in the entity.

For example, age attribute of the student entity and the type of the age attribute can be defined as below −

@Column("int") age: integer; // OR @Column({ type: "int" }) age: integer;

Here,

age is the attribute of the entity. In other word, age is a field / column in the student table in the database.

int represent the type of the age column in the database.

TypeORM supports nearly all the types available in the popular database engine. Actually, TypeORM enables different set of types for each database engine. We can use any database type supported by our database engine without any issue.

For example, the type supported by TypeORM for postgresql database engine is as follows −

int, int2, int4, int8, smalpnt, integer, bigint, decimal, numeric, real, float, float4, float8, double precision, money, character varying,

varchar, character, char, text, citext, hstore, bytea, bit, varbit, bit

varying, timetz, timestamptz, timestamp, timestamp without time zone, timestamp with time zone, date, time, time without time zone, time with time zone, interval, bool, boolean, enum, point, pne, lseg, box, path, polygon, circle, cidr, inet, macaddr, tsvector, tsquery, uuid, xml, json, jsonb, int4range, int8range, numrange, tsrange, tstzrange, daterange, geometry, geography, cube

Similarly, TypeORM supports a different set of datatype for MySQL.

Column Options

TypeORM provides an extensive set of options other than type to describe the column. For example, length option refers the length of the database field and it can be specified as below −

@Column("varchar", { length: 100 })

Some of the most common column options are as follows −

name − Name of the database field / column.

length − Length of the database field / column.

nullable − Specify whether the database field / column allows null or not.

default − Default value of the database field / column.

primary − Specify whether the database field / column is primary key of the table.

unique − Specify whether the database field / column is unique

*precision** − Precision of the database field / column

scale − Scale of the database field / column

comment − Comment or description of the database field / column

@Generated decorator

TypeORM provides additional decorator, @Generated to auto generate the column values. For example, Universally Unique Identifier (UUID) is quite common to use in database to store unique value in a column. The sample code to generate UUID is as follows −

@Entity() 
export class Student {
 
   @PrimaryColumn() 
   id: number; 
   
   @Column() 
   @Generated("uuid") 
   uuid: string; 
}

Here,

uuid is generated automatically and stored inside the database.

Primary columns

At least one primary column field is mandatory for any entity in database. It is classified into different types of decorators. We will discuss it one by one.

@PrimaryColumn()

@PrimaryColumn() decorator is used to create primary column for any type of data. Simple example is shown below,

import {Entity, PrimaryColumn} from "typeorm"; 

@Entity() 
export class Student {        
@PrimaryColumn() 
   id: number; 
}

Here,

id is an integer, which doesn’t accept duppcate values, but we need to assign values.

We can assign primary column for one or more fields as well, if the situation demands.

Example

import {Entity, PrimaryColumn} from "typeorm"; 

@Entity() 
export class Student { 
   
   @PrimaryColumn() 
   id: number; 
   
   @PrimaryColumn() 
   email: string; 
   
   @PrimaryColumn() 
   phone: number; 
}

@PrimaryGeneratedColumn()

@PrimaryGeneratedColumn() field is used to specify the primary column as well as to auto generate the column value in the database. It is shown below −

import {Entity, PrimaryGeneratedColumn} from "typeorm"; 

@Entity() 
export class Student {

   @PrimaryGeneratedColumn() 
   id: number;
}

Here,

You don’t have to assign id value; it will be generated automatically by the TypeORM in the database table.

@PrimaryGeneratedColumn(“uuid”)

@PrimaryGeneratedColumn also accepts an argument to specify the type of generator. One of the main use is to generate unique id based on UUID.

import {Entity, PrimaryGeneratedColumn} from "typeorm";

@Entity() 
export class Student {  
   @PrimaryGeneratedColumn("uuid") id: string; 
}

simple-array column type

Advanced relational database supports array datatype. To support the array datatype, TypeORM provides a special column type, *simple-array" to store primitive array values. A sample code to use it is as follows −

@Entity() 
export class Student { 
   
   @PrimaryGeneratedColumn() 
   id: number;

   @Column("simple-array") 
   names: string[]; 
}

simple-json column type

Lot of modern database engine supports JSON database. To use JSON datatype, TypeORM provides a special type, single-json. The sample code to use it is as follows −

@Entity() 
export class Student { 

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column("simple-json")
   info: { firstName: string, middleName: string, lastName: string }; 
}

This value can be defined in index.ts as,

index.ts

const stud = new Student(); 
stud.info = { firstName: "John", middleName: "peter", lastName: "Michael" };

Special columns

TypeORM supports the following special columns

@CreateDateColumn − It is a special column to set entity’s insertion date automatically.

@UpdateDateColumn − It is used to set the entity’s update time automatically.

@VersionColumn − Set version number for entity automatically.

Entity Inheritance

Entity inheritance is use to reduce duppcation of entities. Consider the below entities −

Result.ts

@Entity() 
export class Result {    

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   title: string; 
   
   @Column() 
   description: string; 
   
   @Column() 
   epgible: string 
}

Grade.ts

The code for grade.ts is as follows −

@Entity() 
export class Grade {

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string; 
   
   @Column() 
   title: string; 
   
   @Column() 
   description: string;
   
   
   
   @Column() 
   grading : string; 
}

Here,

The above two entities have columns id, title and description. Using entity inheritance, we create one base class Details and combine the above two entities as specified below.

Details.ts

export abstract class Details {

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   title: string; 
   
   @Column() 
   description: string; 
} 
@Entity() 
export class Result extends Details{  

   @Column() 
   epgible: string 
} 
@Entity() 
export class Grade extends Details{   

   @Column() 
   name : string; 
   
   @Column() 
   grading : string; 
}

Now start your server, you could see the below response,

Now open your mysql server and move to your database, you could see the following tables,

Grade table

Result table

TypeORM - Relations

Relations are used to refer the relationship between table in database. In general, a relationship exists between two tables when one of them has a foreign key that references the primary key of the other table. This feature makes relational database more powerful and efficiently store information.

TypeORM allows the entities to be related to each other and subsequently database tables. In general, relationship can be classified into four broader categories. They are as follows,

one-to-one − One object of the given entity relates to only one object of the target entity and vice versa. For example, a country will have only one capital city and similarly a city will be capital of only one country.

many-to-one − Multiple object of the given entity relates to one object of the target entity. For example, city comes under only one country but country can have multiple cities.

one-to-many − Same as many-to-one except the relationship is reversed.

many-to-many − Multiple object of the given entity relates to multiple object of the target entity. For example, an article may be tagged under multiple topic pke programming language, finance, etc., and at the same time a particular tag may have multiple articles as well.

TypeORM also provides options to enhance the relationship of the entities. They are as follows −

eager − Source entity object loads the target entity objects as well.

cascade − Target entity object gets inserted or updated while the source entity object is inserted or updated.

onDelete − Target entity objects get deleted as well while the source entity object is deleted.

primary − Used to specify that the relation column is primary key or not.

nullable − Used to specify that the relation column is nullable or not.

Let us go through different types of relation mapping in detail.

One-to-One

As we learned earper, it is referred by the instance of one table field contains the instance of another table field and vice versa. Let us create a Details table −

Details.ts

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";

@Entity() 
export class Details {
   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   gender: string; 
   
   @Column() 
   country: string; 
}

Let’s create an another entity Customer as follows −

Customer.ts

import {Entity, PrimaryGeneratedColumn, Column, OneToOne, JoinColumn} from "typeorm"; 

import {Details} from "./Details"; 

@Entity() 
export class Customer { 

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string; 
   
   @OneToOne(type => Details) @JoinColumn() 
   details: Details;
}

Here,

We have added mapping OneToOne to Details table. @JoinColumn() contain a “relation id” and foreign key to Customer table. We can save the relation in index.ts as follows −

const details = new Details(); details.gender = "female"; details.country = "india" await connection.manager.save(details);

const customer = new Customer(); customer.name =  customer1 ; customer.details = Details; await connection.manager.save(Customer);

One-to-Many and Many-to-One

As we learned earper, it is referred by the instance of first table field contains the multiple instances of second table field called One-to-Many mapping and multiple instances of first table contains only one instance of second table called Many-to-One mapping.

Consider an example of Student and project entities whereas, student can work on more than one project but each project is handled by only one student.

Let’s create a Project entity as follows −

Project

import {Entity, PrimaryGeneratedColumn, Column, ManyToOne} from "typeorm"; import {Student} from "./Student"; 
@Entity() 
export class Project {  

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   projects: string; 
   
   @ManyToOne(type => Student, student => student.projects) student: Student; 
}

Now, we create Student entity as below −

import {Entity, PrimaryGeneratedColumn, Column, OneToMany} from "typeorm"; import {Project} from "./Project"; 

@Entity() 
export class User {  
   
   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string; 
   
   @OneToMany(type => Project, project => project.student) projects: Project[];  
}

Here,

@OneToMany property mapped Project and @ManyToOne property mapped to Student. However, @OneToMany cannot exist without @ManyToOne and @ManyToOne property contain “relation id” and foreign key.

We can save the connection in index.ts as follows −

const proj1 = new Project(); proj1.projects = "database management"; await connection.manager.save(proj1); 

const proj2 = new Project(); proj2.projects = "web apppcation"; await connection.manager.save(proj2); 

const stud = new Student(); stud.name = "Student1"; stud.projects = [proj1, proj2]; await connection.manager.save(stud);

Many-to-Many

As we learned earper, it is referred by multiple records in one table are related to multiple records in another table. Consider an example, University student can be enrolled in multiple classes at a time which means student may have four or five classes per semester and a class can have many students.

We can simply conclude, a student has many classes, and a class has many students. Let’s create an entity for Classes as follows −

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; 

@Entity() 
export class Classes { 

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string; 
}

Now, we create Student entity as below −

import {Entity, PrimaryGeneratedColumn, Column, ManyToMany, JoinTable} from "typeorm"; 
import {Classes} from "./Classes";

@Entity() 
export class Student { 

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string;

   @Column() 
   subjects: string; 
   
   @ManyToMany(type => Classes) @JoinTable() 
   classes: Classes[];
}

TypeORM - Working with Repository

Repository is specific to an entity. In other words, each entity will have its own, build-in repository and it can be accessed using getRepository() method of connection object as specified below −

const studRepository = manager.getRepository(Student);

Once the student repository object is created, it can be used to do all database operation of student object.

Repository types

Repository is classified into four categories. They are as follows −

Repository

Default repository of an entity and it can be accessed using getRepository() method as specified below −

const studRepository = manager.getRepository(Student);

Now, studRepository can be used to query student table

TreeRepository

Used for tree pke structure entities and it can be accessed using getTreeRepository() method as specified below −

const studcaRepository = manager.getTreeRepository(Student);

MongoRepository

Used inside mongoDB operation entities and it can be accessed using getMongoRepository() method as specified below −

const detailsRepository = manager.getMongoRepository(Details);

CustomRepository

Used to customize the repository and it can be accessed using getCustomRepository() method as specified below,

const myUserRepository = manager.getCustomRepository(UserRepository);

Repository API

Let us learn most important method of the EntityManager in this chapter.

manager

We can access EntityManager using manager method as specified below −

const manager = repository.manager;

queryRunner

queryRunner method returns custom query runner object and it is used for database operations by repository. The sample code is as follows −

const queryRunner = repository.queryRunner;

metadata

metadata returns repository’s metadata. The sample code is as follows −

const metadata = repository.metadata;

query

query method executes SQL queries. Simple select query as shown below −

const qur = await repository.query(`select * from students`);

insert

insert method is used to insert a new entity or array of entities to the database. The sample code is as follows −

await repository.insert({ 
   Name: "Student3", 
   Age: 14 
});

The above query is equivalent to,

insert into student(Name,age) values("Student3",14)

update

update is used to update the existing records in the database.

await repository.update(1, { Name: "Adam" });

This query works similar to the one mentioned below −

update student SET Name = "Adam" where id = 1

delete

delete method will delete the specified record from the table,

await repository.delete(Student, 1);

This will delete student with id 1 from the student table. It is equivalent to,

delete from student where id=1;

If you want to delete by name then use the below query,

await repository.delete({ Name: "Student1" });

This query will delete all the student having name, Student1

** softDelete and restore **

It is used to soft delete the data and you can restore the record based on the id of the student. The sample code is as follows −

await repository.softDelete(1);

You can restore the student record using below command −

await repository.restore(1);

An alternative option to delete and restore is to use softRemove and recover methods. The sample code is as follows −

//find the entities const enty = await repository.find(); 

//soft removed entity const entySoftRemove = await repository.softRemove(enty);

And, you can recover them using recover method as specified below,

await repository.recover(entySoftRemove);

save

save is used to save the given entity into the database. Simple Student entity can be save as shown below −

import {Student} from "./entity/Student"; 

createConnection().then(async connection => {                     
   console.log("Inserting a new record into the student database..."); 
   const stud = new Student();
   stud.Name = "student1"; 
   stud.age = 12; 
   await repository.save(stud);

This will add new student record into the database.

remove

remove is used to delete the given entity from the database. Simple Student entity can be deleted as shown below −

await repository.remove(stud);

count

count method will return the number of records available in the table and you can use it pagination purposes. The sample code is as follows −

const cnt = await repository.count(Student, { age: 12 });

find

find method is used for searching purposes. It fetches all the record from database as shown below −

const result = await repository.find({ id: 1 });

findOne

Similar to find method, but returns the first matched record. The sample code is as follows −

const result = await repository.findOne({ id: 1 });

clear

clear method clears all the data from the table. The sample code is as follows −

await repository.clear();

TypeORM - Working with Entity Manager

EntityManager is similar to Repository and used to manage database operations such as insert, update, delete and load data. While Repository handles single entity, EntityManager is common to all entities and able to do operations on all entities.

Entity Manager API

We can access EntityManager using getManager() method as specified below −

import { getManager } from "typeorm"; const entityManager = getManager();

Let us learn most important method of the EntityManager in this chapter.

connection

connection method returns database ORM connection to specific databases. The sample code is as follows −

const connection = manager.connection;

QueryRunner

queryRunner method returns custom query runner object and it is used for database operations by entity manager. The sample code is as follows −

const queryRunner = manager.queryRunner;

transaction

If multiple database requests are called, transaction will execute in a single database transaction. The sample code to get the transaction is as follows −

await manager.transaction(async manager => { 
});

query

query method executes sql queries. Simple insert query as shown below −

const qur = await manager.query(`insert into student(name,age) values( stud2 ,13)`);

insert

insert method is used to insert a new entity or array of entities to the database. The sample code is as follows −

await manager.insert(Student, { 
   Name: "Student3", 
   Age: 14 
});

update

update is used to update the existing records in the database.

await manager.update(User, 1, { Name: "Adam" });

This query works similar to the below SQL query,

UPDATE student SET Name = "Adam" WHERE id = 1

delete

delete method will delete the specified record from the table,

await manager.delete(Student, 1);

This will delete with id 1 of student record.

save

save is used to save the given entity into the database. Simple Student entity can be save as shown below −

import {Student} from "./entity/Student";

createConnection().then(async connection => {   
   console.log("Inserting a new record into the student database..."); 
   const stud = new Student(); stud.Name = "student1"; 
   stud.age = 12; 
   await connection.manager.save(stud); 
}

This will add new student record into the database. save method will insert the student, if the given student does not exist in the database. Otherwise, save will update existing student record in the database.

remove

remove is used to delete the given entity from the database. Simple Student entity can be deleted as shown below −

await manager.remove(stud);

count

count method will return the number of records available in the table and you can use it pagination purposes. The sample code is as follows −

const cnt = await manager.count(Student, { age: 12 });

find

find method is used for searching purposes. It fetches all the record from database as shown below −

console.log("Loading users from the database..."); 
const students = await connection.manager.find(Student); console.log("Loaded users: ", students);

findOne

Similar to find method, but returns the first matched record. The sample code is as follows −

const stud = await manager.findOne(Student, 1);

clear

clear method clears all the data from the table. The sample code is as follows −

await manager.clear(Student);

TypeORM - Query Builder

Query builder is used build complex SQL queries in an easy way. It is initiapzed from Connection method and QueryRunner objects.

We can create QueryBuilder in three ways.

Connection

Consider a simple example of how to use QueryBuilder using connection method.

import {getConnection} from "typeorm"; 

const user = await getConnection() .createQueryBuilder() 
.select("user") 
.from(User, "user") 
.where("user.id = :id", { id: 1 }) .getOne();

Entity manager

Let’s create a query builder using entity manager as follows −

import {getManager} from "typeorm"; 

const user = await getManager() .createQueryBuilder(User, "user") .where("user.id = :id", { id: 1 })    .getOne();

Repository

We can use repository to create query builder. It is described below,

import {getRepository} from "typeorm"; 

const user = await getRepository(User) .createQueryBuilder("user") .where("user.id = :id", { id: 1 }) .getOne();

Apases

Apases are same as SQL apas. We create apas for Student table using QueryBuilder as described below −

import {getConnection} from "typeorm"; 

const user = await getConnection() .createQueryBuilder() 
.select("stud") 
.from(Student, "stud")

This query is equivalent to,

select * from students as stud

Parameters

Parameters are used as placeholders for the dynamic values in the query. In many cases, the query to find different entity object will be same except values. For example, the query to find different student is same except the Student ID data. In this case, we can use parameter for Student ID and then change the parameter to get the different student objects.

Another important use of parameter is to prevent SQL injection. It is one of the important security breach in the modern web apppcation. By using parameter in the query, we can survive the SQL injection attacks.

Another important use of parameter is to prevent SQL injection. It is one of the important security breach in the modern web apppcation. By using parameter in the query, we can survive the SQL injection attacks.

For example

"student.id = :id", { id: 1 }

Here,

:id - parameter name.

{ id: 1 } - value of the parameter

Adding expression

This section explains about how to use expressions.

where

where is used to filter the records if the condition is matched.

createQueryBuilder("student") .where("student.id = :id", { id: 1 })

This query is equivalent to,

select * from students student where student.id=1;

We can also use AND, OR, NOT, IN conditions inside.

having

Simple having expression is defined below −

createQueryBuilder("student") .having("student.id = :id", { id: 1 })

This query is equivalent to,

select * from students student having student.id=1;

orderBy

orderby is used to sort the records based on the field.

createQueryBuilder("student") .orderBy("student.name")

This query is equivalent to,

select * from students student order by student.name;

groupBy

It is used to group the records based on the specified column.

createQueryBuilder("student") .groupBy("student.id")

This query is equivalent to,

select * from students student group by student.id;

pmit

It is used to pmit the selection of rows. Below, example shows how to use pmit in query builder,

createQueryBuilder("student") .pmit(5)

This query is equivalent to,

select * from students student pmit 5;

offset

Offset is used to specify, how many rows to skip the result. It is defined below −

createQueryBuilder("student") .offset(5)

This query is equivalent to,

select * from students student offset 5;

joins

join clause is used to combine rows from two or more tables, based on a related column. Consider the two entities −

Student.ts

import {Entity, PrimaryGeneratedColumn, Column, OneToMany} from "typeorm"; 
import {Project} from "./Project"; 

@Entity() 
export class User {
   
   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string; 
   
   @OneToMany(type => Project, project => project.student) projects: project[]; 
}

Project.ts

import {Entity, PrimaryGeneratedColumn, Column, ManyToOne} from "typeorm"; 
import {Student} from "./Student"; 

@Entity() 
export class Project { 

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   title: string; 
   
   @ManyToOne(type => Student, student => student.projects) student: Student; 
}

Let us perform simple left join using the below query −

const student = await createQueryBuilder("student") .leftJoinAndSelect("student.projects", "project") 
.where("student.name = :name", { name: "Student1" }) 
.getOne();

This query is equivalent to,

SELECT student.*, project.* FROM students student 
   LEFT JOIN projects project ON project.student = student.id 
   WHERE student.name =  Student1 

Similarly, we can try inner join as well.

Join without selection

We can join data without using select. Let us try this example using Inner join as follows −

const student = await createQueryBuilder("student") .innerJoin("student.projects", "project") 
   .where("student.name = :name", { name: "student1" }) 
   .getOne();

The above query is equivalent to −

SELECT student.* FROM students student 
   INNER JOIN projects project ON project.student = student.id 
   WHERE student.name =  Student1 ;

Pagination

If you have more data in your apppcation, you need pagination, page spder or scrolpng functionapties.

For example, if you want to show first five students projects in your apppcation,

const students = await getRepository(Student) .createQueryBuilder("student") .leftJoinAndSelect("student.projects", "project") 
   .take(5) 
   .getMany();

subqueries

It is called query within another query or nested query. We use subqueries in FROM, WHERE and JOIN expressions.

Simple example is shown below −

const projects = await connection .createQueryBuilder() .select("project.id", "id")
.addSelect(subQuery => { 
   return subQuery 
      .select("student.name", "name") .from(Student, "student") 
      .pmit(1); 
}, "name")
.from(Project, "project") .getMany();

Hidden field

If any of your column field is marked as {select: false} then that column is considered as hidden column. Consider the below entity −

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; 

@Entity() 
export class Student {

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string; 
   
   @Column({select: false}) 
   address: string; 
}

Here,

address field is marked as hidden. We can use addSelect method to retrieve the information from the column. It is defined below,

const student = await connection.getRepository(Student) .createQueryBuilder() .select("student.id", "student")    .addSelect("student.address") .getMany();

getSql()

This method is used to get the generated SQL query by query builder. It is defined below −

const sql = createQueryBuilder("student") .where("student.name = :name", { name: "Student1" })  .orWhere("student.age = :age", { age: 14 }) 
.getSql();

TypeORM - Query Operations

Data manipulation is used to manage and view data. This section explains about how to access database queries pke insert, update, select and delete queries using QueryBuilder. Let’s go through one by one in detail.

Build insert query

Let us create a Customer entity as follows −

Customer.ts

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; 
@Entity() 
export class Customer {       

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   name: string; 
   
   @Column() 
   age: number; 
}

Let’s add the following changes in index.ts as follows −

index.ts

import "reflect-metadata"; 
import {createConnection} from "typeorm"; 
import {Customer} from "./entity/Customer"; 
import {getConnection} from "typeorm"; 

createConnection().then(async connection => { 
   await getConnection().createQueryBuilder()   .insert() 
      .into(Customer)  
      .values([ { name: "Adam",age:11}, 
         { name: "David",age:12} ]) .execute(); 
}).catch(error => console.log(error));

Now, start your apppcation using the below command −

npm start

Output

You could see the following output on your screen −

Now open your mysql server, table inserted with two fields as shown below −

Build update query

Last section, we have inserted two rows of data. Let’s check how update query works. Add the following changes in index.ts as follows −

import "reflect-metadata"; 
import {createConnection} from "typeorm"; 
import {Customer} from "./entity/Customer"; 
import {getConnection} from "typeorm";

createConnection().then(async connection => { 

await getConnection()         
   .createQueryBuilder() .update(Customer) 
   .set({ name: "Michael" }) .where("id = :id", { id: 1 }) .execute(); 
   console.log("data updated"); 
   
}).catch(error => console.log(error));

Now, start your apppcation using the below command −

npm start

You could see the following output on your screen −

Mysql table is modified as shown below −

Build select query

select query is used to display the records from the table. Let’s add the following code in index.ts as follows −

index.ts

import "reflect-metadata"; 
import {createConnection} from "typeorm"; 
import {Customer} from "./entity/Customer"; 

createConnection().then(async connection => { 

   console.log("Display records from Customer table..."); 
   const cus = new Customer();

   console.log("Loading customers from the database..."); 
   const customers = await connection.manager.find(Customer); console.log("Loaded users: ", customers); 
}).catch(error => console.log(error));

You could see the following output on your screen −

where expression

Let us add where expression in the query to filter the customers. The sample code is as follows −

import "reflect-metadata"; 
import {createConnection} from "typeorm"; 
import {Customer} from "./entity/Customer"; 
import {getConnection} from "typeorm";

createConnection().then(async connection => { 
   const customer = await getConnection() .createQueryBuilder() .select("cus") 
   .from(Customer, "cus") .where("cus.id = :id", { id: 1 }) .getOne(); 
   
   console.log(customer); 
})
.catch(error => console.log(error));

The above program will return first id records. You could see the following output on your screen,

Similarly, you can try other expressions as well.

Build delete query

Last section, we have inserted, updated and select data. Let’s check how delete query works. Add the following changes in index.ts as follows −

import "reflect-metadata"; 
import {createConnection} from "typeorm"; 
import {Customer} from "./entity/Customer"; 
import {getConnection} from "typeorm"; 

createConnection().then(async connection => { 
   await getConnection() .createQueryBuilder() 
   .delete() 
   .from(Customer) 
   .where("id = :id", { id: 1 }) .execute();
console.log("data deleted"); }).catch(error => console.log(error));

You could see the following output on your screen −

And your mysql table is modified as follows −

TypeORM - Transactions

Generally, transaction is a logic unit responsible for execution of data retrieval and updates. This section explains about Transactions in detail.

Creating transactions

We can create a transaction using either connection or EntityManage. Below example is used to specify create connection and save data inside it.

import {getConnection} from "typeorm"; 

await getConnection().transaction(async transactionalEntityManager => { 

   await connection.manager.save(students); 

});

EntityManager is shown below −

import {getManager} from "typeorm";

await getManager().transaction(async transactionalEntityManager => { 
   await transactionalEntityManager.save(students); 
});

Decorators

We have three types of transaction related decorators in TypeORM.

@Transaction - Wraps all the execution in single database transcation.

@TransactionManager - Used to execute queries inside transaction. It is defined below,

@Transaction({ isolation: "SERIALIZABLE" }) 

save(@TransactionManager() manager: EntityManager, student: Student) {     
   return manager.save(student); 
}

Here,

We used SERIALIZABLE isolation level for transaction.

@TransactionRepository - Used to inject transaction in repository. It is defined below,

@Transaction() save(student: Student, @TransactionRepository(Student) studentRepository: 
Repository<Student>) { 
   return studentRepository.save(student); 
}

Transaction in QueryRunner

QueryRunner is used to execute all database queries. It has single database connection. Database transaction can be organized using QueryRunner. Let’s perform single transaction using QueryRunner.

import {getConnection} from "typeorm"; 

// get a connection and create a new query runner 
const connection = getConnection(); const queryRunner = connection.createQueryRunner(); 

// estabpsh real database connection using our new query runner 
await queryRunner.connect(); 

// now we can execute any queries on a query runner, for example: await queryRunner.query("SELECT * FROM students");

Now, start transaction using the below statement −

await queryRunner.startTransaction();

Then, commit and rollback the transaction using the below statement,

try { 
   await queryRunner.commitTransaction(); 
}

If there is any error, it is handled by catch(),

catch (err) { 

   // since we have errors lets rollback changes we made await queryRunner.rollbackTransaction(); 
}

Now, release the queryRunner as below −

finally { 
   
   // you need to release query runner which is manually created: await queryRunner.release(); 
}

TypeORM - Indices

In general, Indexing is a process to optimize the performance of a database by optimizing the data storage. It is used to quickly locate and access the data in a database. This section explains about how to use index in TypeORM. Indices are classified into different types. Let’s go through one by one in detail.

Column indices

We can create index for particular column using @Index. Consider an example of Customer entity as shown below and index defined for firstName column,

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; 

@Entity() 
export class Student { 

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Index() 
   @Column() 
   firstName: string; 
   
   @Column() 
   lastName: string; 
   
   @Column() 
   age: number; 
   
   @Column() 
   address: string; 
}

@Index allow to specify name for an index as well −

@Index("Name-idx") 
@Column() 
firstName: string;

Unique indices

To specify Unique constraints in your column, use the below property −

{ unique: true }

For example, below is the code to specify unique index for Name column −

@Index({ unique: true }) 
@Column() 
firstName: string;

To apply indices for more than one columns, we can directly specify it after @Entity(). The sample code is as follows −

@Entity() 
@Index(["firstName", "lastName"]) @Index(["firstName", "lastName"], { unique: true })

Spatial indices

Spatial index allows to access spatial objects. MySQL and PostgreSQL supports spacial indices. To enable spatial indices in your column, add the following property −

{ spatial: true }

Spatial type has multiple sub types such as, geometry, point, pne string, polygon etc., For example, if you want to add point spatial type in your column, use below code −

@Column("point") 
@Index({ spatial: true }) 
point: string;

Disable synchronization

To disable synchronization, use the below option on @Index decorator −

{ synchronize: false }

TypeORM - Entity Listener and Logging

Entity pstener is used in entities which supports custom method and psten specific events. We can define any entity custom method using decorators. Let’s understand decorators in brief.

@AfterLoad − When the entity is loaded using QueryBuilder or repository/manager, this method will be called.

@BeforeInsert − This method will call before the entity is inserted using repository/manager.

@AfterInsert − This method will call after the entity is inserted using repository/manager.

@BeforeUpdate − This method will call it before an existing entity is updated using repository/manager.

@AfterUpdate − It will call after an entity is updated.

@BeforeRemove − It will call before an entity is removed.

@AfterRemove − It will call after an entity is removed.

Subscriber

Subscriber is used to psten specific entity events. It is implemented from EntitySubscriberInterface. Let’s understand a simple example for how to use entity pstener in subscriber. Consider the Student entity is shown below −

Student.ts

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; 

@Entity() 
export class Student {     

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   Name: string; 
   
   @Column() 
   age: number; 
}

Create student subscriber

Subscriber is created using the below command −

typeorm subscriber:create -n StudentSubscriber

The above command creates a subscriber directory inside your project src. Then, StudentSubscriber.ts file is created inside your subscriber. You could see the following response,

Subscriber /Users/workspace/TypeORM/FirstProject/src/subscriber/StudentSubscriber.ts has been created successfully.

Now move to file, you could see the below coding −

StudentSubscriber.ts

import {EventSubscriber, EntitySubscriberInterface} from "typeorm"; 

@EventSubscriber() 
export class StudentSubscriber implements EntitySubscriberInterface<any> { 
}

Now, add the following changes in the file,

import {EventSubscriber, EntitySubscriberInterface,InsertEvent} from "typeorm"; 
import {Student} from "../entity/Student"; 

@EventSubscriber() 
export class StudentSubscriber implements EntitySubscriberInterface<any> { 
   pstenTo() 
   { 
      return Student; 
   } 
   
   afterInsert(event: InsertEvent<Student>) { 
      console.log(event); 
   } 
}

Here,

We have used afterInsert() method to call the entity event. Similarly, you can use other events as well. We have already configured ormconfig.json file. Now, add the below changes in index.ts file as follows −

index.ts

import "reflect-metadata"; import {createConnection} from "typeorm"; import {Student} from "./entity/Student"; 

createConnection().then(async connection => {

   console.log( connection estabpshed ); 
}).catch(error => console.log(error));

After executing the apppcation, you could see the below output on your screen,

Logging

Database logging is an important part of your highly available database solution design because database logs make it possible to recover from a failure, and they make it possible to synchronize primary and secondary databases.

All databases have logs associated with them. These logs keep records of database changes. If a database needs to be restored to a point beyond the last full, off-pne backup, logs are required to roll the data forward to the point of failure.

Logging options

Logging is enabled by adding {logging: true} in database connection. Logging options are classified into different types. They are as follows −

query − return all log queries. It is defined as given below −

{ 
   host: "localhost",
   ... 
   logging: ["query"] 
}

error − return logs for all failed queries and errors. It is defined below −

{ 
   host: "localhost",
   ... 
   logging: ["error"] 
}

schema − return logs for the schema.

warn − return internal ORM warnings.

info − return logs internal ORM informative messages.

log − return internal ORM log messages.

Custom logger

Custom logging is simple and highly customizable logging option. We can create our own logger class using the below code −

import {Logger} from "typeorm"; 

export class MyCustomLogger implements Logger { 
   
   // implement all methods from logger class 
}

Connection option is specified in ormconfig.json as follows −

name: "mysql", 
type: "mysql", 
host: "localhost", 
port: 3306, 
username: "root", 
password: "root", 
database: "test", 
logger: new MyCustomLogger()

TypeORM with JavaScript

The default language supported by TypeORM is TypeScript. Since, TypeScript supports static typing, classes and decorators, it is easy to define the entity and its attributes. At the same time, JavaScript is necessary as well in certain project where the preferred language is JavaScript. TypeORM provides full support for JavaScript language as well. TypeORM support both es5 and es6 flavors of JavaScript.

In this chapter, let us learn how to write TypeORM apppcation in JavaScript ES5 (ECMAScript 5).

Open a command prompt and go to your workspace.

cd /path/to/workspace/

Run below command to create a TypeORM project.

typeorm init --name typeorm-javascript-student-app --database mysql

Open package.json file to remove the typescipt references.

original

{ 
   "name": "typeorm-javascript-student-app", "version": "0.0.1", 
   "description": "Awesome project developed with TypeORM.", "devDependencies": { 
      "ts-node": "3.3.0", "@types/node": "^8.0.29", "typescript": "3.3.3333" 
   }, 
   "dependencies": { 
      "typeorm": "0.2.24", "reflect-metadata": "^0.1.10", "mysql": "^2.14.1" 
   }, 
   "scripts": { 
      "start": "ts-node src/index.ts" } 
}

updated

{ 
   "name": "typeorm-javascript-student-app", "version": "0.0.1", 
   "description": "Awesome project developed with TypeORM.", "dependencies": { 
      "typeorm": "0.2.24",
      "mysql": "^2.14.1" 
   }, 
   "scripts": { 
   "start": "node src/index.js" 
   } 
}

Here,

Removed the devDependencies section and typescript related package in dependences section.

Changed the start script to point javascript code instead of typescript code.

Run below command to install necessary packages.

npm install

Remove tsconfig.json and index.ts file.

Remove User.ts file inside entity folder and then create student entity in json format, student.json as specified below −

{ 
   "name": "Student", 
   "columns": { 
      "id": { 
         "primary": true, 
         "type": "int", 
         "generated": true 
      }, 
      "name": { 
         "type": "varchar" 
      }, 
      "age": { 
         "type": "integer" 
      } 
   } 
}

Create a new file, src/index.js and put the below code −

var typeorm = require("typeorm"); var EntitySchema = typeorm.EntitySchema; 

typeorm.createConnection({ 
   "type": "mysql", 
   "host": "localhost", 
   "port": 3306, 
   "username": "root", 
   "password": "123456", 
   "database": "typeorm_test_db",
   "synchronize": true, 
   "logging": false, 
   entities: [ new EntitySchema(require("./entity/student.json")) 
   ] 
}) 
.then(function(connection) { 
   return connection.getRepository("Student"); }) .then(function(studentRepository) { 
   var student = { 
      name: "Student1", 
      age: 18 
   }; 
   return studentRepository.save(student) .then(function(savedStudent) { console.log("Student has been successfully saved: ", savedStudent); 
   return studentRepository.find(); }) 
   .then(function(students) { console.log("All students: ", students); 
   return; 
   }) 
   .catch(function(error) { console.log("Error: ", error); return; 
   }) 
}) 
.catch(function(error) { console.log("Error: ", error) 
   return; });

Here,

We have used the same typeORM methods except the below mentioned changes,

Used EntitySchema to configure the student entity.

Used JavaScript Promise concept (then / catch / finally) blocks.

Now, run the apppcation using below command −

npm start

The apppcation inserts the student information into the database and then fetch all student in the database and show it in the console as shown below −

> typeorm-javascript-student-app@0.0.1 start /path/to/workspace/typeorm-javascript-student-app

> node src/index.js 

Student has been successfully saved: { name:  Student1 , age: 18, id: 1 } All students: [ { id: 1, name:  Student1 , age: 18 } ]

TypeORM - Working with MongoDB

This chapter explains the extensive MongoDB database support provided by TypeORM. Hopefully, we have installed mongodb using npm. If it is not installed, use the below command to install MongoDB driver,

npm install mongodb --save

Creating a project

Let’s create a new project using MongoDB as follows −

typeorm init --name MyProject --database mongodb

Configure ormconfig.json

Let’s configure MongoDB host, port and database options in ormconfig.json file as specified below −

ormconfig.json

{ 
   "type": "mongodb", 
   "host": "localhost", 
   "port": 27017, 
   "database": "test", 
   "synchronize": true, 
   "logging": false, 
   "entities": [ 
      "src/entity/**/*.ts" 
   ], 
   "migrations": [ "src/migration/**/*.ts" 
   ], 
   "subscribers": [ "src/subscriber/**/*.ts" 
   ], 
   "cp": { 
      "entitiesDir": "src/entity", "migrationsDir": "src/migration", "subscribersDir": "src/subscriber" 
   } 
}

Define entities and columns

Let us create a new entity named Student inside your src directory. Entities and columns are same. To generate primary key column, we use @PrimaryColumn or

@PrimaryGeneratedColumn. This can be defined as @ObjectIdColumn. Simple example is shown below −

Student.ts

import {Entity, ObjectID, ObjectIdColumn, Column} from "typeorm"; 

@Entity() 
export class Student {  

   @ObjectIdColumn() 
   id: ObjectID; 
   
   @Column() 
   Name: string; 
   
   @Column() 
   Country: string; 
}

To save this entity, open index.ts file and add the following changes −

index.ts

import "reflect-metadata"; 
import {createConnection} from "typeorm"; 
import {Student} from "./entity/Student"; 

createConnection().then(async connection => { 

   console.log("Inserting a new Student into the database..."); const std = new Student(); std.Name = "Student1"; 
   std.Country = "India"; 
   await connection.manager.save(std); console.log("Saved a new user with id: " + std.id); 
   
   console.log("Loading users from the database..."); 
   const stds = await connection.manager.find(Student); console.log("Loaded users: ", stds); 
   
   console.log("TypeORM with MongoDB"); 
}).catch(error => console.log(error));

Now, start your server and you will get the following response −

npm start

MongoDB EntityManager

We can also use EntityManager to fetch data. Simple example is shown below −

import {getManager} from "typeorm";

const manager = getManager(); 
const result = await manager.findOne(Student, { id:1 });

Similarly, we can also use repository to access data.

import {getMongoRepository} from "typeorm"; 

const studentRepository = getMongoRepository(Student); 
const result = await studentRepository.findOne({ id:1 });

If you want to filter the data using equal option as follows −

import {getMongoRepository} from "typeorm"; 

const studentRepository = getMongoRepository(Student); 
const result = await studentRepository.find({ 
   where: { 
      Name: {$eq: "Student1"}, 
   } 
});

As we seen in this chapter, TypeORM makes it easy to work with MongoDB database engine.

TypeORM with Express

Express is one of the popular JavaScript framework to create web apppcation. Let us learn how to use TypeORM along with express framework in this chapter.

Creating a simple apppcation

TypeORM CLI provides an easy option to create a complete working express web apppcation (Restful API apppcation) integrated with TypeORM. The CLI command to create the apppcation is as follows −

cd /path/to/workspace typeorm init --express --name typeorm-express-sample --database mysql

Above command will create a new web apppcation under typeorm-express-sample folder. The structure of the apppcation is as follows −

│ .gitignore 
│ ormconfig.json 
│ package.json 
│ README.md 
│ tsconfig.json 
│ └───src 
      │ index.ts 
      │ routes.ts 
      │ 
      ├───controller 
      │      UserController.ts 
      │ 
      ├───entity 
      │      User.ts 
      │ 
      └───migration

Here,

As we know, ormconfig.json is the TypeORM configuration file. The code is as follows,

{ 
   "type": "mysql", 
   "host": "localhost", 
   "port": 3306, 
   "username": "test", 
   "password": "test", 
   "database": "test", 
   "synchronize": true, 
   "logging": false, 
   "entities": [
      "src/entity/**/*.ts" 
   ], 
   "migrations": [ "src/migration/**/*.ts" 
   ], 
   "subscribers": [ "src/subscriber/**/*.ts" 
   ], 
   "cp": { 
      "entitiesDir": "src/entity", "migrationsDir": "src/migration", "subscribersDir": "src/subscriber" 
   } 
}

Here, change the database setting to match your local database setting.

package.json file is the main configuration of the apppcation.

tsconfig.json file contains the configuration related to TypeScript.

entity folder contains the TypeORM models. A default User model will be created by CLI and it is as follows −

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm"; 

@Entity() 
export class User { 
   
   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   firstName: string; 
   
   @Column() 
   lastName: string; 
   
   @Column() 
   age: number; 
}

controller folder contains the express controllers. CLI create a default user API controller with add / pst / delete user details. The code is as follows −

import {getRepository} from "typeorm"; import {NextFunction, Request, Response} from "express"; import {User} from "../entity/User"; 

export class UserController {

   private userRepository = getRepository(User); 
   
   async all(request: Request, response: Response, next: NextFunction) { 
      return this.userRepository.find(); 
   } 
   
   async one(request: Request, response: Response, next: NextFunction) { 
      return this.userRepository.findOne(request.params.id); 
   } 
   
   async save(request: Request, response: Response, next: NextFunction) { 
      return this.userRepository.save(request.body); 
   } 
   
   async remove(request: Request, response: Response, next: NextFunction) { 
      let userToRemove = await this.userRepository.findOne(request.params.id); 
      await this.userRepository.remove(userToRemove); 
   } 
}

Here,

all method is used to fetch all users from the database.

one method is used to fetch a single user from the database using user id

save method is used to save the user information into the database.

delete method is used to delete the user from the database using user id

routes.ts file maps the user controller methods to proper URL and the code is as follows −

import {UserController} from "./controller/UserController"; 

export const Routes = [{ 
      method: "get", 
      route: "/users", 
      controller: UserController, action: "all" 
   }, { 
      method: "get", 
      route: "/users/:id", controller: UserController, action: "one" 
   }, { 
      method: "post", 
      route: "/users", 
      controller: UserController, action: "save" 
   }, { 
      method: "delete", route: "/users/:id", controller: UserController,
      action: "remove" 
}];

Here,

/users url is mapped to user controller. Each verb post, get and delete are mapped to different methods.

Finally, index.ts is our main web apppcation entry point. The source code is as follows −

import "reflect-metadata"; 
import {createConnection} from "typeorm"; 
import * as express from "express"; import * as bodyParser from "body-parser"; 
import {Request, Response} from "express"; 
import {Routes} from "./routes"; import {User} from "./entity/User"; 

createConnection().then(async connection => { 

   // create express app const app = express(); app.use(bodyParser.json()); 

   // register express routes from defined apppcation routes Routes.forEach(route => { 
      (app as any)[route.method](route.route, (req:   Request, res: Response, next: Function) => { 
         const result = (new (route.controller as any))[route.action](req, res, next); 
         if (result instanceof Promise) { 
            result.then(result => result !== null && result !== undefined ? res.send(result) : undefined); 
         } else if (result !== null && result !== undefined) { 
            .json(result); 
         } 
      }); 
   }); 
      
   // setup express app here 
   // ... 
      
   // start express server app.psten(3000); 
      
   // insert new users for test await connection.manager.save(connection.manager.create(User, { 
      firstName: "Timber",
      lastName: "Saw", 
      age: 27 
   }));
   await connection.manager.save(connection.manager.create(User, { 
      firstName: "Phantom", 
      lastName: "Assassin", 
      age: 24 
   })); 
      
   console.log("Express server has started on port 3000. Open http://localhost:3000/users to see results"); 
}).catch(error => console.log(error));

Here, the apppcation configures the routes, insert two users and then start the web apppcation at port 3000. We can access the apppcation at http://localhost:3000

To run the apppcation, follow below steps −

Let us install the necessary packages using below command −

npm install

Output

npm notice created a lockfile as package-lock.json. You should commit this file. 
npm WARN typeorm-express-sample@0.0.1 No repository field. 
npm WARN typeorm-express-sample@0.0.1 No pcense field. 

added 176 packages from 472 contributors and audited 351 packages in 11.965s 

3 packages are looking for funding  run `npm fund` for details 

found 0 vulnerabipties

Run the below command to start the apppcation.

npm start

Output

> typeorm-express-sample@0.0.1 start /path/to/workspace/typeorm-express-sample 
> ts-node src/index.ts 

Express server has started on port 3000. Open http://localhost:3000/users to see results

Let us access our web apppcation API using curl command as below −

curl http://localhost:3000/users

Here,

curl is a command pne apppcation to access web apppcation from command prompt. It supports all the HTTP verbs such as get, post, delete, etc.,

Output

[{"id":1,"firstName":"Timber","lastName":"Saw","age":27},{"id":2,"firstName":"Phantom","lastName":"Assassin","age":24}]

To fetch the first record, we can use below command −

curl http://localhost:3000/users/1

Output

{"id":1,"firstName":"Timber","lastName":"Saw","age":27}

To delete a user record, we can use below command −

curl -X DELETE http://localhost:3000/users/1

As we seen in this chapter, TypeORM can be easily integrated into express apppcation.

TypeORM - Migrations

Migrations are pke version control for your database. It is used to modify and share apppcation’s database schema. This section explains about how migrations works in TypeORM.

Creating new migration

To create a new migration, first we need to setup connection in ormconfig.json. It is defined below −

ormconfig.json

"type": "mysql", 
"host": "localhost", 
"port": 8889, 
"username": "root", 
"password": "root", 
"database": "Library", 
"entities": ["entity/*.js"], "migrationsTableName": "student_migration_table", "migrations": ["migration/*.js"], "cp": { 
   "migrationsDir": "migration" 
}

Here,

migrationsTableName − it refers the migration table name.

migrations − TypeORM loads migrations from given directory.

cp − indicates migration will create inside the specific directory.

Create Book entity

Let’s create an entity named Book entity inside src/entity/Book.ts as follows −

import { Entity, Column, PrimaryGeneratedColumn } from  typeorm ; 
@Entity() 
export class Book { 

   @PrimaryGeneratedColumn() 
   id: number; 
   
   @Column() 
   title: string;
   
   @Column() 
   text: string; 
}

Execute CLI to create new migration

Now, we can execute new migration using CLI as follows −

Syntax

typeorm migration:create -n <migration-name>

Example

typeorm migration:create -n myMigration

After executing the above command, you could see the below response −

Migration /path/to/project/src/migration/1587101104904-myMigration.ts has been generated successfully.

Now, move inside src/migration/1587101104904-myMigration.ts file looks similar to this.

import {MigrationInterface, QueryRunner} from "typeorm"; 

export class myMigration1587101104904 implements MigrationInterface {      

   pubpc async up(queryRunner: QueryRunner): Promise<any> { 
   } 
   
   pubpc async down(queryRunner: QueryRunner): Promise<any> { 
   } 
}

Here,

We have two methods up and down. up method is used to add changes to the migration and down method is used to revert changes in your migration.

Let us add up method inside myMigration.ts file as specified below −

import {MigrationInterface, QueryRunner} from "typeorm"; 

export class Book1587131893261 implements MigrationInterface { 

   pubpc async up(queryRunner: QueryRunner): Promise<any> { 
      await queryRunner.query(`ALTER TABLE book ADD COLUMN price int`); 
   }
   pubpc async down(queryRunner: QueryRunner): Promise<any> { } 
}

Here,

We have added a new column price inside book table. Now, execute the CLI to add the above changes.

ts-node ./node_modules/typeorm/cp.js migration:run

The above command executes migrations and run them in a sequence. Now, you could see the below changes in your screen −

Output

Now open your mysql server, new column is added. It is shown below −

Similarly, We can modify column title datatype to varchar(30) as follows,

import {MigrationInterface, QueryRunner} from "typeorm"; 

export class Book1587131893261 implements MigrationInterface { 

   pubpc async up(queryRunner: QueryRunner): Promise<any> { 
   await queryRunner.query(`ALTER TABLE book MODIFY COLUMN title varchar(30)`); 
      } 
   pubpc async down(queryRunner: QueryRunner): Promise<any> { 
   } 
}

Now, execute the same command and you could the below changes −

ts-node ./node_modules/typeorm/cp.js migration:run

Output

Book table is modified as,

Revert migration

Let’s add the below code inside down method to revert migration −

import {MigrationInterface, QueryRunner} from "typeorm"; 

export class Book1587131893261 implements MigrationInterface { 
   
   pubpc async up(queryRunner: QueryRunner): Promise<any> { 
   
   } 
   pubpc async down(queryRunner: QueryRunner): Promise<any> { 
   
      await queryRunner.query(`ALTER TABLE book drop column price`); // reverts things made in "up" method
   } 
}

Now, execute the below command to revert all the changes −

ts-node ./node_modules/typeorm/cp.js migration:revert

You could see the following response −

Output

Book table is modified as,

Output

As we seen in this chapter, TypeORM makes it easy to write database migration script.

TypeORM - Working with CLI

This section explains about TypeORM CLI commands in detail.

Create TypeORM project

typeorm init is the easiest and fastest way to setup a TypeORM project. You can create a new project as,

typeorm init --name Demoproject --database mysql

After executing the command, you will get the following output on your screen −

Project created inside /Users/workspace/TypeORM/Demoproject directory.

Create an entity

To create a new entity using CLI as,

typeorm entity:create -n Person

Now, Person entity is created inside your project src directory.

Entity /Users/workspace/TypeORM/Demoproject/src/entity/Person.ts has been created successfully.

If you have a multi-module project structure with multiple entities in different directories, you can use the below command,

typeorm entity:create -n Person -d src/Person/entity

Create a new subscriber

To create a new subscriber using CLI as follows −

typeorm subscriber:create -n PersonSubscriber

You could see the following response −

Subscriber /path/to/TypeORM/Demoproject/src/subscriber/PersonSubscriber.ts has been created successfully.

Create migrations

You can create a new migration using CLI as mentioned below −

typeorm migration:create -n PersonMigration

The above command created a migration directory inside your project src. Migration files are stored inside it.

Migration /path/to/TypeORM/Demoproject/src/migration/1587395030750-PersonMigration.ts has been generated successfully.

Database schema

To synchronize a database schema, use the below command −

typeorm schema:sync

To completely drop a database schema, use the below command −

typeorm schema:drop

Sql queries

If you want to execute any sql queries, we can execute directly from here. For example, to display all the records of customers, use the below query −

typeorm query "select * from customers"

If you want to clear everything stored in the cache. You can do it using the following command −

typeorm cache:clear

Conclusion

TypeORM is an excellent open source ORM framework to create high quapty and scalable apppcations from small scale apppcations to large scale enterprise apppcations with multiple databases.