SQLAlchemy ORM - Using Query

All SELECT statements generated by SQLAlchemy ORM are constructed by Query object. It provides a generative interface, hence successive calls return a new Query object, a copy of the former with additional criteria and options associated with it.

Query objects are initially generated using the query() method of the Session as follows −

q = session.query(mapped class)

Following statement is also equivalent to the above given statement −

q = Query(mappedClass, session)

The query object has all() method which returns a resultset in the form of pst of objects. If we execute it on our customers table −

result = session.query(Customers).all()

This statement is effectively equivalent to following SQL expression −

SELECT customers.id 
AS customers_id, customers.name 
AS customers_name, customers.address 
AS customers_address, customers.email 
AS customers_email
FROM customers

The result object can be traversed using For loop as below to obtain all records in underlying customers table. Here is the complete code to display all records in Customers table −

from sqlalchemy import Column, Integer, String
from sqlalchemy import create_engine
engine = create_engine( sqpte:///sales.db , echo = True)
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class Customers(Base):
   __tablename__ =  customers 
   id = Column(Integer, primary_key =  True)
   name = Column(String)

   address = Column(String)
   email = Column(String)

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind = engine)
session = Session()
result = session.query(Customers).all()

for row in result:
   print ("Name: ",row.name, "Address:",row.address, "Email:",row.email)

Python console shows pst of records as below −

Name: Ravi Kumar Address: Station Road Nanded Email: ravi@gmail.com
Name: Komal Pande Address: Koti, Hyderabad Email: komal@gmail.com
Name: Rajender Nath Address: Sector 40, Gurgaon Email: nath@gmail.com
Name: S.M.Krishna Address: Budhwar Peth, Pune Email: smk@gmail.com

The Query object also has following useful methods −