How to add new field to existing django model postgres

Question

Let's suppose I have the following model:

class Test(models.Model):
   field_one = models.CharField(max_length=80)

Now, we have created 2-3 Model objects with field_one field.

p1 = Test(field_one="Object1")
p1.save()
p2 = Test(field_one="Object2")
p2.save()

Later, I realised that I need to add another field field_two to my Test model.

class Test(models.Model):
   field_one = models.CharField(max_length=80)
   field_two = models.IntegerField(default=3)

Now, Doing makemigrations & migrate and running server.

which will prompt the following error

django.db.utils.ProgrammingError: column mainapp_test.field_two does not exist

I understand that this error occurs due to my 2 existing objects in PostGresDB doesn't have field_two column.

Is there any effective way to add field_two column to my existing objects with some default value? or How to solve this problem?

Django Version: 2.0 Django ORM DB: PostGresql

can you show the relevant part migration file generated by makemigrations? — radoh
– radoh, Commented Oct 16, 2019 at 18:07

Fasand · Accepted Answer · 2019-10-16 17:43:08Z

1

When you add a field to an existing model, you must either provide a default value in the code, or set it to null/blank = True, or provide a one-off default while migrating.

Since you are providing a default in the code, the migration should run without issues. At least from experience, I've added several BooleanFields with default=False to my existing model with thousands of entries, and I never got a ProgrammingError.

Have you tried shutting down the Postgres backend before running makemigrations and migrate? I would think Django would do this but that's the only thing I can think of. Also, obviously, shut down the Django server if it's still running.

answered Oct 16, 2019 at 17:43

Fasand

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1 Comment

Arbazz Hussain Over a year ago

You are right, but i did messed but with my migrations , had to delete a column of django_migrations to get it fixed.

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