MySQL in some situations will generate spurious remove_constraint

[sqlalchemy-bot]

Migrated issue, originally created by Johannes Erdfelt (@jerdfelt)

If a table includes a unique index with the same name as a column, the correct_for_autogen_constraints code for MySQL will remove it. This will cause the autogenerate code to generate a spurious remove_constraint.

The attached script reproduces the problem.

I have a patch and unit test that fixes the problem by ignoring unique indexes in correct_for_autogen_constraints since MySQL will never implicitly create a unique index.

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Attachments: mysql_testcase.py

[sqlalchemy-bot]

Changes by Johannes Erdfelt (@jerdfelt):

• changed title from "MySQL in some situations will generatespurious rem" to "MySQL in some situations will generate spurious re"

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

MySQL: Ignore unique indexes when removing implicit indexes

MySQL will implicitly create indexes when using foreign keys. Alembic
attempts to remove those implicit indexes so they don't appear as
removes when comparing metadata.

However, unique indexes with the same name as a column are considered
as possibly implicitly created causing alembic to emit a spurious
'remove_constraint'.

Since MySQL will never implicitly create unique indexes, they can be
safely ignored when removing the implicit indexes.

Fixes #251

→ 22667c1

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

see also c307d22

[sqlalchemy-bot]

Johannes Erdfelt (@jerdfelt) wrote:

Thanks for the quick merge.

FWIW, I ran into this because of this unique index in Nova:

https://github.com/openstack/nova/blob/master/nova/db/sqlalchemy/models.py#L158

The recent fixes to alembic have made the autogenerate functionality much better.