Add article with Alembic foreign key listing/updating

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

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+---
+layout:    post
+title:     "Rename automatically named foreign keys with Alembic"
+date:      2017-01-02 09:41:23
+tags:      [mysql, development, flask, python]
+published: true
+author:
+    name: Gergely Polonkai
+    email: 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](http://www.binarytides.com/list-foreign-keys-in-mysql/).
+
+``` sql
+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'])`