Re: Meta indexes and makemigrations

Hi,

The issue is that partial indexes with conditions (condition attribute in models.Index) were introduced in Django 3.2, but they rely on the database backend's ability to support them. PostgreSQL does support partial indexes, so that part should be fine. However, your problem likely stems from the following points:

1. Condition on channel_type Value

The condition models.Q(channel_type="42") is valid in Python, but PostgreSQL requires conditions to work with literal values that match the column type. If channel_type is a CharField, "42" is fine. However, ensure that the value and type match your database schema.

• Example: If channel_type is actually an integer-like value stored in a CharField, ensure "42" matches the expected format.

---

2. Potential Issue with Makemigrations

Even if the code is correct, makemigrations might not detect the change in the Meta class because migrations only track model-level changes. If makemigrations doesn't pick up the index:

• Manually Generate the Migration: Use makemigrations with the --empty flag and define the index manually.

  python manage.py makemigrations --empty your_app_name  

  Then, in the generated migration file, define the index:

  from django.db import migrations, models  import django.db.models.expressions    class Migration(migrations.Migration):      dependencies = [          ('your_app_name', 'previous_migration'),      ]        operations = [          migrations.AddIndex(              model_name='episode',              index=models.Index(                  name='ch_last_seen_date',                  fields=['last_seen_date'],                  condition=models.Q(channel_type='42'),              ),          ),      ]  

---

3. Check Your Environment

Ensure your Django project environment is up-to-date and consistent:

• Confirm your django.db.backends.postgresql version supports the feature.
• Run python manage.py showmigrations to ensure your migrations are applied.

---

Debugging Steps

1. Double-check the condition syntax:

   condition=models.Q(channel_type='42')  

   Ensure channel_type and '42' match your schema's type expectations.

2. Confirm makemigrations is running in the correct app and picking up changes:

   python manage.py makemigrations your_app_name  

3. Review your migration file for errors or omissions.

If the issue persists after these steps, consider upgrading to the latest Django version for potential bug fixes in migration handling. 

On Thu, Dec 5, 2024 at 4:11 PM mccc <mciccozz@gmail.com> wrote:

Hello,

We want to have a partial index (db backend is Postgres) on a datetimefield, so we added this code to the Meta class:

class Episode(models.Model):

    channel_type = models.CharField(max_length=16, choices=CHANNEL_TYPES)

    last_seen_date = models.DateTimeField(auto_now_add=True)

    class Meta:
        indexes = [
            models.Index(
                name="ch_last_seen_date",
                fields=["last_seen_date"],
                condition=models.Q(channel_type="42"),
            ),
        ]

The problem is that makemigrations doesn't seem to recognize it.

What could be the problem? We're on Django 3.2, which I know is old but as per the documentation this should be fine..

Thanks

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Thanks and Regards

J. Ranga Bharath

cell: 9110334114

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