Casting Char Field to Integer in Django ORM

When querying with Django ORM, you may encounter scenarios where you need to cast a character field to an integer. This can arise when the field is stored as a CharField but you want to perform calculations or comparisons using integer values.

Why CAST is Unavailable?

In earlier versions of Django, raw SQL queries or database functions were necessary for such scenarios. However, with the introduction of Cast function in Django 1.10, you can achieve this casting within the ORM itself.

Using the Cast Function

To cast a CharField to an integer, use the following syntax:

from django.db.models import Cast, IntegerField

students.objects.annotate(
    student_id_int=Cast('student_id', IntegerField())
).filter(student_id_int__contains=97318).order_by('-student_id_int')

This will annotate the queryset with a new field called student_id_int, which is cast to an integer type. You can then use this new field for filtering and ordering as desired.

Benefits of Using Cast

Using Cast provides several benefits:

• Type-safe: Ensures that the resulting value is of the specified type.
• Avoids Raw Queries: Keeps your queries within the ORM, simplifying maintenance and reducing the risk of SQL injection.
• Efficient: Performs the casting efficiently at the database level.

Reference

For more information on casting in Django ORM, refer to the documentation:

• [Database Functions: Cast](https://docs.djangoproject.com/en/stable/ref/models/database-functions/#cast)