Altering CharFields to have both db_index=True and unique=True crashes on postgresql

[Karl Hobley]

Hi Everyone,

If you have a CharField with db_index=True and alter it to have both "db_index=True" and "unique=True" the migration for this will not run on PostgreSQL.

Instead, you will get the following error:

django.db.utils.ProgrammingError: relation "app_mymodel_my_field_3922656f_like" already exists

This bug apears to have been introduced in Django 1.8.7/1.9.1. Git bisect leads to this commit: ​https://github.com/django/django/commit/722fae4b5159b2810e252e3385936f86f04eb09b

I have created a test project that should hopefully help diagnosis: ​https://github.com/kaedroho/djangobugtest2/

Thanks,

Karl

[Tim Graham]

Docs say, "Note that when unique is True, you don’t need to specify db_index, because unique implies the creation of an index." Nonetheless, we should handle this case gracefully.

[Simon Charette]

i wonder if this could be related to #25694.

[Tim Graham]

​PR (have to double check a few things tomorrow, so not checking 'has patch' yet)

[Tim Graham <timograham@…>]

In 56aaae58:

Fixed #26034 -- Fixed incorrect index handling on PostgreSQL on Char/TextField with unique=True and db_index=True.

Thanks Simon Charette for review.

[Tim Graham <timograham@…>]

In 3d324b9:

[1.9.x] Fixed #26034 -- Fixed incorrect index handling on PostgreSQL on Char/TextField with unique=True and db_index=True.

Thanks Simon Charette for review.

Backport of 56aaae58a746eb39d5e92ba60f59f4c750a8e1a8 from master

[Tim Graham <timograham@…>]

In f8c3d38c:

[1.8.x] Fixed #26034 -- Fixed incorrect index handling on PostgreSQL on Char/TextField with unique=True and db_index=True.

Thanks Simon Charette for review.

Backport of 56aaae58a746eb39d5e92ba60f59f4c750a8e1a8 from master

[Tim Graham <timograham@…>]

In 497b5d6:

Refs #26034 -- Added another case fixed by this ticket to release notes.

Thanks Shai Berger for the report.

[Tim Graham <timograham@…>]

In 5e8685c:

Refs #26034 -- Added another case fixed by this ticket to release notes.

[Tim Graham <timograham@…>]

In 4aec49d:

[1.9.x] Refs #26034 -- Added another case fixed by this ticket to release notes.

Thanks Shai Berger for the report.

Backport of 497b5d6feee5b7947231bd0ae6edf833773b6cce and
5e8685c1b14e94e3f540ac1d68b61e71dcc27517 from master

[Tim Graham <timograham@…>]

In 7b6ab28:

[1.8.x] Refs #26034 -- Added another case fixed by this ticket to release notes.

Thanks Shai Berger for the report.

Backport of 497b5d6feee5b7947231bd0ae6edf833773b6cce from master

[Tim Graham <timograham@…>]

In d47f6d75:

Refs #26034 -- Corrected a schema test to work with the correct field state.

[Tim Graham <timograham@…>]

In 5c048524:

[1.10.x] Refs #26034 -- Corrected a schema test to work with the correct field state.

Backport of d47f6d75ef67dbd18abf2bb927753f739a9c117d from master

[Tim Graham <timograham@…>]

In 54c0dea:

[1.9.x] Refs #26034 -- Corrected a schema test to work with the correct field state.

Backport of d47f6d75ef67dbd18abf2bb927753f739a9c117d from master