Django ORM Queries

Insert Data with Django ORM

To create an object of model Album and save it into the database, we need to write the following command:

>>> a = Album(title = "Divide", artist = "Ed Sheeran", genre = "Pop")
>>> a.save()

To create an object of model Song and save it into the database, we need to write the following command:

>>> s = Song(name = "Castle on the Hill", album = a)
>>> s.save()

Creating Data with Django ORM

Let us add 2 more Albums records for the sake of demonstration.

>>> a = Album(title = "Abbey Road", artist = "The Beatles", genre = "Rock")
>>> a.save()
>>> a = Album(title = "Revolver", artist = "The Beatles", genre = "Rock")
>>> a.save()

Retrieving Data with Django ORM

To retrieve all the objects of a model, we write the following command:

>>> Album.objects.all()
<QuerySet [<Album: Divide>, <Album: Abbey Road>, <Album: Revolver>]>

The output is a QuerySet, or a set of objects that match the query. Notice that the name printed is the output of the __str__() function. We can also filter queries using the functions filter(), exclude() and get(). The filter() function returns a QuerySet having objects that match the given lookup parameters.

>>> Album.objects.filter(artist = "The Beatles")
<QuerySet [<Album: Abbey Road>, <Album: Revolver>]>

The exclude() function returns a QuerySet having objects other than those matching the given lookup parameters.

>>> Album.objects.exclude(genre = "Rock")
<QuerySet [<Album: Divide>]>

The get() function returns a single object which matches the given lookup parameter. It gives an error when the query returns multiple objects.

>>> Album.objects.get(pk = 3)
<QuerySet [<Album: Revolver>]>

Update Data with Django ORM

We can modify an existing object as follows:

>>> a = Album.objects.get(pk = 3)
>>> a.genre = "Pop"
>>> a.save()

Deleting Data with Django ORM

To delete a single object, we need to write the following commands:

>>> a = Album.objects.get(pk = 2)
>>> a.delete()
>>> Album.objects.all()
<QuerySet [<Album: Divide>, <Album: Revolver>]>

To delete multiple objects, we can use filter() or exclude() functions as follows:

>>> Album.objects.filter(genre = "Pop").delete()
>>> Album.objects.all()
<QuerySet []>

Django lets us interact with its database models, i.e. add, delete, modify, and query objects, using a database-abstraction API called ORM(Object Relational Mapper). This article discusses all the functional operations we can perform using Django ORM.

Prerequisite: Django models