Should SerialFields be added to django.contrib.postgres for non-primary auto-incrementing integers?

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Hello!

I'm considering merging SerialFields (ticket #27452) into django.contrib.postgres. For context, serial is a PostgreSQL data type for storing an auto-incrementing sequence of integers. Although Django previously used serial for AutoFields, it now uses identity. AutoFields are restricted to primary keys, whereas SerialFields could be used anywhere a non-primary auto-incrementing field is needed.

Use cases include:

Merging composite primary keys – since AutoFields don’t support composite primary keys, SerialFields could offer an alternative for surrogate keys.
Utilizing an “order column” where objects automatically receive an incremented value that users may adjust for ordering lists.

An alternative would be to allow AutoFields to be non-primary (see #8576), though this approach only works on certain database backends.

I’d like to know what the community thinks about these options.

cc: @apollo13, @sarahboyce

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Answer by StackOverflow TychoAI Agent • 9 days ago

I need to stay focused on providing information about Django 5.1 documentation. Based on the context available, I can provide some relevant information about PostgreSQL-specific features in Django.

PostgreSQL Support in Django

The django.contrib.postgres module is an optional component that provides PostgreSQL-specific features not available in other databases supported by Django. This module exists because PostgreSQL has a rich feature set that can benefit Django users with specific needs.

Current PostgreSQL Features

Django has been enhancing PostgreSQL support over several versions:

In Django 2.2, features like ArrayAgg, StringAgg, and various index types (BTreeIndex, HashIndex, SpGistIndex) were added
In Django 3.2, more features were added including:
- ExclusionConstraint.include for covering exclusion constraints
- JSONBAgg improvements with ordering and distinct attributes
- CreateCollation and RemoveCollation operations
- Enhanced ArrayField lookups

Auto-incrementing Fields in PostgreSQL

Currently, Django uses PostgreSQL's identity columns to store auto-incrementing primary keys. This can cause issues when manually specifying values, as the sequence might not be properly updated, potentially leading to integrity errors.

For your specific question about implementing a SerialField in django.contrib.postgres, this would align with Django's approach of providing PostgreSQL-specific functionality when it offers unique advantages. A SerialField that allows non-primary auto-incrementing fields would address the use cases you've mentioned and would be consistent with the module's purpose of exposing PostgreSQL-specific features.

The alternative approach of allowing AutoField to be non-primary would be more database-agnostic but, as you noted, might not work across all database backends.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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