gergelypolonkai-web-jekyll/_posts/2017-01-02-rename-automatically-named-foreign-keys-with-alembic.md

layout	title	date	tags	published	author
post	Rename automatically named foreign keys with Alembic	2017-01-02 09:41:23	mysql development flask python	true	name email Gergely Polonkai gergely@polonkai.eu

I have recently messed up my Alembic migrations while modifying my SQLAlchemy models. To start with, I didn’t update the auto-generated migration files to name the indexes/foreign keys a name, so Alembic used its own naming scheme. This is not an actual problem until you have to modify columns that have such constraints. I have since fixed this problem, but first I had to find which column references what (I had no indexes other than primary key back then, so I could go with foreign keys only). Here is a query I put together, mostly using this article.

SELECT constraint_name,
       CONCAT(table_name, '.', column_name) AS 'foreign key',
       CONCAT(referenced_table_name, '.', referenced_column_name) AS 'references'
FROM information_schema.key_column_usage
WHERE referenced_table_name IS NOT NULL AND
      table_schema = 'my_app';

Now I could easily drop such constraints using alembic.op.drop_constraint('users_ibfk1', 'users', type_='foreignkey') and recreate them with alembic.op.create_foreign_key('fk_user_client', 'users', 'clients', ['client_id'], ['id'])