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Add article with Alembic foreign key listing/updating

sqla-i18n-post
Gergely Polonkai 6 years ago
parent 3734bb67d0
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      _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'])`
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