Dhall definitions

[ilyakooo0]

I think Dhall type definitions for migrations would be a nice thing to have. It would allow typechecking the migration schema without needing to run pgroll and would allow us to write helper functions for more compact schema migration definitions.

I already have rough definitions for the migrations schemas that I use at work: https://gist.github.com/ilyakooo0/1b76cc0b63cb9d8d2e4e9e5c718c2f35

Let me know if this is something you might be interested in. I can provide more details if you need them.

I would also be willing to maintain the definitions in the pgroll repo.

[ilyakooo0]

I can privately provide actual migration that use these definitions if that would be helpful.

[exekias]

Ah nice one, I didn't know about Dhall. We actually leverage JSON Schema to solve this, here you can find the schema definition: https://github.com/xataio/pgroll/blob/main/schema.json, would this be useful in this case? I don't know if Dhall brings some other features that JSON schema lacks

[ilyakooo0]

In Utils.dhall I defined helper functions that simplify describing schema migrations. This allows me to avoid JSON boilerplate.

[ilyakooo0]

This is how a migration might look:

PGRoll.operations
      [ PGRoll.Operation.create_table
          { name = "lang"
          , columns =
            [ Utils.id
            , (Utils.column "name" Rel8.Text)
              with unique = True
            , (Utils.column "abbr" Rel8.Text)
              with unique = True
            , (Utils.column "countryCode" Rel8.Text)
              with unique = True
            ]
          }
      ]

[ilyakooo0]

There are additional bonuses like LSP support and diffing.

[ilyakooo0]

You could also provide Dhall functions that convert old schemas to new schemas.