inspectdb should introspect autofield

[Paul Dejean]

My models.py was full of stuff like:
day_id = models.IntegerField(primary_key=True)
Due to the naming convention that we prefer for our primary keys.

I actually wasn't aware of AutoField until just now, and thought that primary keys not being made auto increment was by design for some reason.

[Claude Paroz]

None of the Django core backends support AutoField introspection yet. However, inspectdb should add a hint as a comment (# AutoField?) in the resulting output. Apparently, it's the best we can do currently.

If you think you can add AutoField introspection in some Django core backend or if the comment mentioned above is not present, feel free to reopen the ticket with some more information.

[Paul Dejean]

Replying to claudep:

None of the Django core backends support AutoField introspection yet. However, inspectdb should add a hint as a comment (# AutoField?) in the resulting output. Apparently, it's the best we can do currently.

If you think you can add AutoField introspection in some Django core backend or if the comment mentioned above is not present, feel free to reopen the ticket with some more information.

Which core backends don't support autofield introspection? It must be sqlite3 or oracle, since MySQL supports everything iirc, and Postgre supports everything and then some.

[Claude Paroz]

There is a can_introspect_autofield flag set to False in django/db/backends/__init__.py, and this flag is not set anywhere else (see c89d80e2cc9bf1f401aa3af4047bdc6f3dc5bfa4). I'm not saying that core backends *cannot* introspect AutoField, but currently none of them implement the needed discovery code.

[Collin Anderson]

Opening this for if someone wants to implement the introspection. (Though, it's not a bug.)

[Claude Paroz]

PR for MySQL and PostgreSQL: ​https://github.com/django/django/pull/3579

[Claude Paroz <claude@…>]

In 11662022be261d9a926b763e9fecc9f55ac3514a:

Added AutoField introspection for MySQL

Refs #23748.

[Claude Paroz <claude@…>]

In 1a63093e22a18688914a82651c461e2ea89cd564:

Added AutoField introspection for PostgreSQL

Refs #23748.

[Mariusz Felisiak]

In ​9af6c97504ef2b06dd5292d03ea94d3eb5d8c4d6

Added AutoField introspection on Oracle.

[Tim Graham]

It looks like the remaining task for this ticket is to add introspection on SQLite (if the column definition includes AUTOINCREMENT).

[Nick Pope]

Replying to Tim Graham:

It looks like the remaining task for this ticket is to add introspection on SQLite (if the column definition includes AUTOINCREMENT).

So I've looked into rounding out the introspection support for AutoField - here is a ​PR for SQLite.

It really turns out to be quite simple. According to the documentation AUTOINCREMENT can only be used with INTEGER PRIMARY KEY which is automatically an alias of ROWID that actually provides unique incremented values. AUTOINCREMENT merely changes the algorithm used, but is usually not necessary and ought to be avoided. See ​here and ​here for details.

There are two things to be aware of:

1. It is not possible to introspect BigAutoField as BIGINT PRIMARY KEY cannot have AUTOINCREMENT and does not alias ROWID. I disabled the test for SQLite.
2. No effort is made to check for composite primary keys, but I don't think we do for other backends. We just assume the first INTEGER PRIMARY KEY column is the AutoField.

[Nick Pope]

​PR has been updated following reviews.
I have used Refs instead of Fixed, so this ticket will need closing once merged as SQLite is the final backend to be implemented.

[Tim Graham <timograham@…>]

In a35d2a45:

Refs #23748 -- Added AutoField introspection for SQLite.