autogenerate breaks on fk specified on remote name when remote key != name

[sqlalchemy-bot]

Migrated issue, originally created by dataradiant (@dataradiant)

I have a foreign key where the remote column is referenced by name and link_to_name=True. When using autogenerate, I receive a KeyError on the column name here: https://bitbucket.org/zzzeek/alembic/src/feaea56b97a11f4f132fb5f55d8a6b71dc0b9c04/alembic/autogenerate/render.py?at=master&fileviewer=file-view-default#render.py-685

It's trying to lookup the column using the string provided, which in this case is the name rather than the key, which obviously doesn't work so well when they aren't the same.

Replacing that line with a conditional that checks for link_to_name seems to work at least for my case:

if fk.link_to_name:
    colname = _ident(colname)
else:
    colname = _ident(parent_metadata.tables[table_fullname].c[colname].name)

[sqlalchemy-bot]

Changes by dataradiant (@dataradiant):

• edited description

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

here's the funniest part of that function:

"""Implement a 'safe' version of ForeignKey._get_colspec() that
never tries to resolve the remote table."""

then

try to resolve the remote table and adjust for column.key

what a letdown.

as for the issue, need a reproducer. Guess this is just the render() operation.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

the two options here would be either to also replicate the "link_to_name=True" flag if we are still linking to name, or to replace the name with the key if we've resolved it.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

nevermind, i recall we are just trying to render for DB-direct operations only

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

https://gerrit.sqlalchemy.org/571

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• added labels: autogenerate - rendering

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

Clean up _fk_colspec() for link_to_name, no column found

A :class:.ForeignKeyConstraint can now render correctly if the
link_to_name flag is set, as it will not attempt to resolve the name
from a "key" in this case. Additionally, the constraint will render
as-is even if the remote column name isn't present on the referenced
remote table.

Change-Id: Ic030fbc106973231b6877c1acfb5349e515335a8
Fixes: #456

→ 0a0524d

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed