Add prefix option to check repo status plug

[stevehodgkiss]

When developing an app that uses schema-based multi-tenancy, it would be useful to be able to configure another CheckRepoStatus plug for a named "dev" tenant:

    plug Phoenix.Ecto.CheckRepoStatus, otp_app: :myapp

    plug Phoenix.Ecto.CheckRepoStatus,
      otp_app: :myapp,
      migration_paths: &Myapp.Release.tenant_migrations_path/1,
      prefix: "tenant_acme"

migration_opts has been add to PendingMigrationError, so the configured prefix and migration_lock options are used when the "Run migrations for repo" action is triggered.

[josevalim]

Instead of prefix, what if we allow migration_paths to be {path, opts} pairs? This way you can specify opts per path?

[stevehodgkiss]

Yeah, that would be more flexible & wouldn't require multiple plug configurations.

defmodule MyMod do
  def migrations_paths(repo) do
    default_migrations_path = Migrator.migrations_path(repo)

    tenant_migrations_path =
      Path.join(default_migrations_path, "../tenant_migrations") |> Path.expand()

    [default_migrations_path, {tenant_migrations_path, prefix: "tenant_acme"}]
  end
end

# endpoint

    plug Phoenix.Ecto.CheckRepoStatus,
      otp_app: :myapp,
      migration_paths: &MyMod.migrations_paths/1

Could also fetch the tenant schema names from the db rather than use a fixed value. Will update tomorrow 😄

[stevehodgkiss]

I've updated the PR to allow tuples in migration_paths. There's a slight change in behaviour in 5648d73, where given fn -> ["a", "b"] end it'll run the migrator once for a and again for b.

I'm not sure how well the option name migration_paths fits with this new functionality. Alternative names could be migrate_runs or a migrate: fn -> ["a", {"b", prefix: "tenant"}]. Thoughts?

[josevalim]

Ouch, I am sorry. I think the change in behaviour is not acceptable because it does change how the migrator sees and runs migrations. I think your original version is the way to go indeed. Can you please revert? And thank you for exploring this path. :)

[stevehodgkiss]

I've reverted 6c36d02 which means the migrator will run once for the ["a", "b"] case (although the code to maintain this behaviour is a bit complicated). Oh, did you mean revert back to the original version with the prefix option (i.e. to include only the first 2 commits in this PR)?

[josevalim]

Rollback to the original version. It would require you to list the plug twice but I think that's alright?

[stevehodgkiss]

Reverted to the original version. Yeah, listing the plug twice is fine for this use case (a known dev tenant prefix).

[josevalim]

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