String cursor migration is not reversible

[ibrahima]

I'm trying out this gem, and I got this error when trying to reverse the migrations so that I could work on a different branch.

== 20240817025553 ChangeCursorToString: reverting =============================
-- change_table(:maintenance_tasks_runs)
bin/rails aborted!
StandardError: An error has occurred, this and all later migrations canceled: (StandardError)

PG::DatatypeMismatch: ERROR:  column "cursor" cannot be cast automatically to type bigint
HINT:  You might need to specify "USING cursor::bigint".
/app/db/migrate/20240817025553_change_cursor_to_string.maintenance_tasks.rb:16:in `block in down'
/app/db/migrate/20240817025553_change_cursor_to_string.maintenance_tasks.rb:15:in `down'

Caused by:
ActiveRecord::StatementInvalid: PG::DatatypeMismatch: ERROR:  column "cursor" cannot be cast automatically to type bigint (ActiveRecord::StatementInvalid)
HINT:  You might need to specify "USING cursor::bigint".
/app/db/migrate/20240817025553_change_cursor_to_string.maintenance_tasks.rb:16:in `block in down'
/app/db/migrate/20240817025553_change_cursor_to_string.maintenance_tasks.rb:15:in `down'

I think maybe the way to fix this would be to change it to this:

  def down
    change_table(:maintenance_tasks_runs) do |t|
      t.change(:cursor, "bigint USING cursor::bigint")
    end
  end

I was a bit confused about how to apply the hint but then I found this https://stackoverflow.com/a/44132110 but at least in this case I don't think it's necessary to use the CAST function explicitly. I expect that it's largely moot anyway since people probably won't be reversing this in production, only in development environments where they're testing it out.

Thanks!

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