manager.has_index for migrations

[IgnisDa]

Motivation

The SchemaManager has convenience methods like has_table and has_column while writing migrations. I propose a has_index method.

Proposed Solutions

It will return true if an index exists for a given table.

Current Workarounds

Execute the query manually.

If accepted I would like to make a PR.

[IgnisDa]

For reference, here are the queries:

-- SQLITE
SELECT EXISTS (
    SELECT 1
    FROM sqlite_master
    WHERE type = 'index'
      AND name = 'metadata_identifier__index'
      AND tbl_name = 'metadata'
) AS index_exists;

-- POSTGRES
SELECT EXISTS (
    SELECT 1
    FROM pg_indexes
    WHERE schemaname = 'public'
      AND tablename = 'metadata'
      AND indexname = 'metadata_identifier__index'
) AS index_exists;

-- MYSQL
SELECT EXISTS (
    SELECT 1
    FROM INFORMATION_SCHEMA.STATISTICS
    WHERE TABLE_SCHEMA = 'your_database_name'
      AND TABLE_NAME = 'metadata'
      AND INDEX_NAME = 'metadata_identifier__index'
) AS index_exists;

[tyt2y3]

Sure. Such a feature would be welcomed. The relevant code should go into SeaSchema and then wrapped in SeaORM.

[IgnisDa]

@tyt2y3 Thanks for the hint. For Postgres and MySQL(?) do I need to schema into account or do I assume that we are working with the public schema?

EDIT: NVM figured it out.

[IgnisDa]

@tyt2y3 Made the PRs.