Foreign key creation fails if table has already a foreign key to referenced table

[sqlalchemy-bot]

Migrated issue, originally created by Lucas Kahlert (@f3anor)

If you create add a column incl. a foreign key with a batch operation, e.g.

with op.batch_alter_table('quest') as batch_op:
    batch_op.add_column(sa.Column('therapist_id', sa.String(255), nullable=True))
    batch_op.create_foreign_key('fk_quest_therapist_id_user', 'user', ['therapist_id'], ['username'])

but the referenced table (user) was already created, because there is another column in quest referring to user, the upgrade command will produce the follwing error:

InvalidRequestError: Table 'user' is already defined for this MetaData instance.  Specify 'extend_existing=True' to redefine options and columns on an existing Table object.

[sqlalchemy-bot]

Michael Bayer (@zzzeek) wrote:

• Fixed bug in batch where if the target table contained multiple
  foreign keys to the same target table, the batch mechanics would
  fail with a "table already exists" error. Thanks for the help
  on this from Lucas Kahlert. fixes #254

→ b20ad56

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed