gergelypolonkai-web-jekyll/content/blog/2017-01-02-rename-automatically-named-foreign-keys-with-alembic.rst

Rename automatically named foreign keys with Alembic

date

2017-01-02T09:41:23Z

category

blog

tags

mysql,development,flask,python

url

2017/01/02/rename-automatically-named-foreign-keys-with-alembic/

save_as

2017/01/02/rename-automatically-named-foreign-keys-with-alembic/index.html

status

published

author

Gergely Polonkai

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'])