Peewee - User defined Operators

Peewee has Expression class with the help of which we can add any customized operator in Peewee’s pst of operators. Constructor for Expression requires three arguments, left operand, operator and right operand.

op=Expression(left, operator, right)

Using Expression class, we define a mod() function that accepts arguments for left and right and ‘%’ as operator.

from peewee import Expression # the building block for expressions

def mod(lhs, rhs):
   return Expression(lhs,  % , rhs)

Example

We can use it in a SELECT query to obtain pst of records in Contacts table with even id.

from peewee import *
db = SqpteDatabase( mydatabase.db )

class BaseModel(Model):
   class Meta:
      database = db

class Contacts(BaseModel):
   RollNo = IntegerField()
   Name = TextField()
   City = TextField()

db.create_tables([Contacts])

from peewee import Expression # the building block for expressions

def mod(lhs, rhs):
   return Expression(lhs, % , rhs)
qry=Contacts.select().where (mod(Contacts.id,2)==0)
print (qry.sql())
for q in qry:
   print (q.id, q.Name, q.City)

This code will emit following SQL query represented by the string −

( SELECT "t1"."id", "t1"."RollNo", "t1"."Name", "t1"."City" FROM "contacts" AS "t1" WHERE (("t1"."id" % ?) = ?) , [2, 0])

Output

Therefore, the output is as follows −

2  Amar Delhi
4  Leena Nasik
6  Hema Nagpur
8  John Delhi
10 Raja Nasik