35 lines
1.4 KiB
Markdown
35 lines
1.4 KiB
Markdown
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---
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layout: post
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title: "Rename automatically named foreign keys with Alembic"
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date: 2017-01-02 09:41:23
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tags: [mysql, development, flask, python]
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published: true
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author:
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name: Gergely Polonkai
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email: gergely@polonkai.eu
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---
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I have recently messed up my Alembic migrations while modifying my
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SQLAlchemy models. To start with, I didn’t update the auto-generated
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migration files to name the indexes/foreign keys a name, so Alembic used its
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own naming scheme. This is not an actual problem until you have to modify
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columns that have such constraints. I have since fixed this problem, but
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first I had to find which column references what (I had no indexes other
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than primary key back then, so I could go with foreign keys only). Here is
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a query I put together, mostly using
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[this article](http://www.binarytides.com/list-foreign-keys-in-mysql/).
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``` sql
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SELECT constraint_name,
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CONCAT(table_name, '.', column_name) AS 'foreign key',
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CONCAT(referenced_table_name, '.', referenced_column_name) AS 'references'
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FROM information_schema.key_column_usage
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WHERE referenced_table_name IS NOT NULL AND
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table_schema = 'my_app';
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```
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Now I could easily drop such constraints using
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`alembic.op.drop_constraint('users_ibfk1', 'users', type_='foreignkey')` and
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recreate them with `alembic.op.create_foreign_key('fk_user_client', 'users',
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'clients', ['client_id'], ['id'])`
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