Schema changes without breaking Questions

1

How can we make schema changes without breaking all our existing Questions (on Postgres)?

For example:

  • Rename tables
  • Rename columns
  • Move tables to other schemas

What internal Metabase table holds the actual table/columns/query for each Question? What caches would we need to clear, and how? We’re not afraid to get our hands dirty.

Thank you!

2

You could change the Metabase database, but it’s a lot to get right!

What if you just created views to match the existing tables? That way the questions would just hit the views instead of the change tables.

4

For future searchers, here’s how we moved tables to a different Postgres schema:

  • Move the tables with alter table set schema
  • In the Metabase DB, update metabase_table set schema = 'newschema' where schema = 'oldschema' and db_id = 9
  • On /admin/databases/9, click “Sync database schema now”

Questions are still working as before.

We also wrote a script to make sure all questions are still working. It uses the API to get the IDs of all non-archived questions, then POSTs to /api/card/NNN/query, and asserts that the “status” field is “completed”.

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