Query

Q - query node

Used to build filters based on binary operators. Helps build more complex database queries

Q is a class that allows us to make complex database queries. For example, if we need to make a logical query with the operators "and", "or" or even combine several operators at once. By itself, Q is not intended to be used like regular classes. This class is based on logical operators, with the help of which it builds a query.

Let's analyze the simplest example of how a query is built using Q:

from models_manager import Q

Q(id__in=(1, 2, 3))
'"{model}"."id" IN (1, 2, 3)'

From the example above, we can see that our python code has turned into SQL code, thanks to the Q class.

id converted to "{model}"."id"
__in converted to SQL IN
(1, 2, 3) converted to SQL (1, 2, 3)

Now let's complicate the example and add a few more arguments to our Q

from models_manager import Q

Q(id__in=(1, 2, 3), id__lt=5)
'"{model}"."id" IN (1, 2, 3) AND "{model}"."id" < 5'

id converted to "{model}"."id"
__lt converted to SQL <
5 converted to 5

Note

Note that our expressions are now connected with the AND operator, which is the default for such expressions. But it can be changed by passing the default argument inside our Q

from models_manager import Q

Q(id__in=(1, 2, 3), id__lt=5, default=Q.OR)
'"{model}"."id" IN (1, 2, 3) OR "{model}"."id" < 5'

Now we see that the expressions are connected via the OR operator.

Let's now connect the two examples above. To be shared by the AND operator

from models_manager import Q

Q(id__in=(1, 2, 3), id__lt=5) | Q(id__in=(1, 2, 3), id__lt=5, default=Q.OR)
"""
("{model}"."id" IN (1, 2, 3) AND "{model}"."id" < 5) 
OR 
("{model}"."id" IN (1, 2, 3) OR "{model}"."id" < 5)
"""

We got an example, which is connected, through the OR operator

Consider the use of logical operators on the example of the user model

from models_manager import Model, Field
from models_manager.utils import random_number, random_string


class User(Model):
    identity = 'users'
    database = 'stuff'

    id = Field(default=random_number, category=int)
    username = Field(default=random_string, category=str)
    email = Field(default=random_string, category=str)

    def __str__(self):
        return f'<User: {self.id}>'

OR

| - Bitwise OR

from models_manager import Q

User.manager.filter(Q(id__in=(1, 2)) | Q(username='some'))

AND

& - Bitwise AND

from models_manager import Q

User.manager.filter(Q(id__in=(1, 2)) & Q(username='some'))

OR + AND

from models_manager import Q

User.manager.filter(
    (Q(id__in=(1, 2)) & Q(username='some')) |
    (Q(id__lt=100) & Q(username__like='other'))
)

Above were an example of how you can build logical expressions for database queries