#35180: PostgreSQL pattern ops indexes are dropped when changing between
CharField
and TextField
-------------------------------------+-------------------------------------
Reporter: Robin Ray | Owner:
| timbaginski
Type: Bug | Status: closed
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution: duplicate
Keywords: index postgres | Triage Stage:
migration | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by timbaginski):
Replying to [comment:3 Natalia Bidart]:
> Hello Robin Ray, thank you for your report and for helping making Django
better.
>
> As far as I can see, this is a valid issue. When I first read the
description, I was sure there were already similar reports so I searched a
bit for possible duplicates. I couldn't find an exact duplicate but there
are related issues reported (and fixed in some cases) in #25412, #34505,
and a few others involving collations.
>
> It seems that the code at fault is the `_alter_field` in
`django/db/backends/postgresql/schema.py` that skips creating the index
because `old_field.db_index` and `new_field.db_index` are both True. I'm
not an expert in this area so I have added some people as cc in this
ticket, but I think this guard needs to also consider whether the column
being altered is also changing its type:
>
> {{{#!python
> diff --git a/django/db/backends/postgresql/schema.py
b/django/db/backends/postgresql/schema.py
> index 842830be30..975a9f1e93 100644
> --- a/django/db/backends/postgresql/schema.py
> +++ b/django/db/backends/postgresql/schema.py
> @@ -295,10 +295,12 @@ class
DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
> new_db_params,
> strict,
> )
> + type_changed = old_type != new_type
> + old_db_index = old_field.db_index or old_field.unique
> + new_db_index = new_field.db_index or new_field.unique
> + needs_index = (not old_db_index and new_db_index) or
(type_changed and new_db_index)
> # Added an index? Create any PostgreSQL-specific indexes.
> - if (not (old_field.db_index or old_field.unique) and
new_field.db_index) or (
> - not old_field.unique and new_field.unique
> - ):
> + if needs_index:
> like_index_statement = self._create_like_index_sql(model,
new_field)
> if like_index_statement is not None:
> self.execute(like_index_statement)
> }}}
>
> **NOTE:** please do not consider this diff as suitable for a patch
without further discussion.
I've been looking at it and noticed the exact same thing. I think you just
need to add a condition to check if the old field was type varchar or text
and got changed.
{{{
# Added an index or deleted index due to type change?
# Create any PostgreSQL-specific indexes.
if (not (old_field.db_index or old_field.unique) and
new_field.db_index) or (
not old_field.unique and new_field.unique) or
((old_field.db_index or old_field.unique) and (
(old_type.startswith("varchar") and not
new_type.startswith("varchar"))
or (old_type.startswith("text") and not
new_type.startswith("text")))
):
like_index_statement = self._create_like_index_sql(model,
new_field)
if like_index_statement is not None:
self.execute(like_index_statement)
}}}
EDIT: I'm new to open source contribution, so my apologies if my claiming
of the ticket and subsequent lack of communication caused any headache
--
Ticket URL: <https://code.djangoproject.com/ticket/35180#comment:7>
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