Adding a SearchVectorField to a model in Django

Question

So I'm trying to add a SearchVectorField to a model in Django:

class JobPosting(models.Model):
    ...
    ...
    search_vector = SearchVectorField()

I get that it should either be nullable or have a default value to be able to migrate so I deleted all entries in the table to prevent this problem.

However, I'm getting the following error when running makemigrations:

You are trying to add a non-`nullable` field 'search_vector' to jobposting without a default;
we can't do that (the database needs something to populate existing rows).
Please select a fix:
   1) Provide a one-off default now
      (will be set on all existing rows with a null value for this column)
   2) Quit, and let me add a default in models.py
Select an option:

Why is it saying this if the table is empty? I don't want to make the column nullable, and I'd rather not have a default value if I can avoid it.

My question is, is there any way to force makemigrations and migrate as I don't understand the problem if the table is empty. I have other tables with data in them which I don't want to delete so can't delete all info in the database.

Alternatively, if option 1) is the solution, how would I format a default value for this type of field? I assume it's not a normal text field?

Thanks for any help.

Answer 1

I am not entirely sure why you do not want to have a default value, but I will assume this as given.

My question is, is there any way to force makemigrations and migrate as I don't understand the problem if the table is empty.

Your current database table might be empty, but migrations are supposed to be repeatable on other database instances. Therefore Django cannot assume that the same holds on any other database.

A workaround might be to do define a migration that creates the field as nullable, indexes all entries and then updates it to be non-nullable.

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.contrib.postgres.search import SearchVector, SearchVectorField      
from django.db import migrations


def index_entries(apps, schema_editor):
    Entry = apps.get_model("mymodel", "Entry")
    Entry.objects.update(search_vector=SearchVector('body_text'))


class Migration(migrations.Migration):

    dependencies = [
        ('mymodel', '0001_initial'),
    ]

    operations = [
        migrations.AddField(
            model_name='entry',
            name='search_vector',
            field=SearchVectorField(null=True),
        ),

        migrations.RunPython(index_entries),

        migrations.AlterField(
            model_name='entry',
            name='search_vector',
            field=SearchVectorField(null=False),
        ),
    ]

Answer 2

I'd just make the field nullable (and probably not editable, since you're not going to change it in admin interface nor via forms):

class JobPosting(models.Model):
    ...
    ...
    search_vector = SearchVectorField(null=True, editable=False)

And there will be no issues with migration.

Later you can make this field not nullable, but there is no real reason to do this because you will update it programmatically anyway.