fab-manager/db/migrate/20220704084929_add_reservation_fields_to_slots_reservations.rb

# Previously, the Slot table was holding data about reservations.
# This was a wrong assumption that leads to a bug.
# An Availability should have many slots but a slot can be related to multiple Reservations,
# so a slot must not hold data about a single reservation (like `offered`),these data
# should be stored in SlotsReservation instead.
class AddReservationFieldsToSlotsReservations < ActiveRecord::Migration[5.2]
  def up
    add_column :slots_reservations, :ex_start_at, :datetime
    add_column :slots_reservations, :ex_end_at, :datetime
    add_column :slots_reservations, :canceled_at, :datetime
    add_column :slots_reservations, :offered, :boolean

    execute %(
      UPDATE slots_reservations
      SET
        ex_start_at=slots.ex_start_at,
        ex_end_at=slots.ex_end_at,
        canceled_at=slots.canceled_at,
        offered=slots.offered
      FROM slots
      WHERE slots_reservations.slot_id = slots.id
    )

    remove_column :slots, :ex_start_at
    remove_column :slots, :ex_end_at
    remove_column :slots, :canceled_at
    remove_column :slots, :offered
    remove_column :slots, :destroying

    # we gonna keep only only one slot (remove duplicates) because data is now hold in slots_reservations

    # update slots_reservation.slot_id
    execute %(
      UPDATE slots_reservations
      SET slot_id=r.kept
      FROM (
          SELECT count(*), start_at, end_at, availability_id, min(id) AS kept, array_agg(id) AS all_ids
          FROM slots
          GROUP BY start_at, end_at, availability_id
          HAVING count(*) > 1) as r
      WHERE slot_id = ANY(r.all_ids);
    )

    # remove useless slots
    execute %q(
     WITH same_slots AS (
         SELECT count(*), start_at, end_at, availability_id, min(id) AS kept, array_agg(id) AS all_ids
         FROM slots
         GROUP BY start_at, end_at, availability_id
         HAVING count(*) > 1
     )
     DELETE FROM slots
     WHERE id IN (SELECT unnest(all_ids) FROM same_slots)
     AND id NOT IN (SELECT kept FROM same_slots);
   )
  end

  def down
    ## FIXME, more than one row returned by a subquery used as an expression
    ## in UPDATE slots_reservations, slot_slots return all inserted ids
    #
    # WITH same_slots AS (
    #     SELECT count(*), array_agg(id) AS all_ids, slot_id
    #     FROM slots_reservations
    #     GROUP BY slot_id
    #     HAVING count(*) > 1
    # ), slot AS (
    #     SELECT *
    #     FROM slots
    #     WHERE id IN (SELECT slot_id FROM same_slots)
    # ), insert_slot AS (
    #     INSERT INTO slots (start_at, end_at, created_at, updated_at, availability_id)
    #     SELECT start_at, end_at, now(), now(), availability_id
    #     FROM slot
    #     RETURNING id
    # )
    # UPDATE slots_reservations
    # SET slot_id=(SELECT id FROM insert_slot)
    # WHERE id IN (SELECT unnest(all_ids) FROM same_slots);
    #

    add_column :slots, :ex_start_at, :datetime
    add_column :slots, :ex_end_at, :datetime
    add_column :slots, :canceled_at, :datetime
    add_column :slots, :offered, :boolean
    add_column :slots, :destroying, :boolean, default: false

    execute %(
      UPDATE slots
      SET
        ex_start_at=slots_reservations.ex_start_at,
        ex_end_at=slots_reservations.ex_end_at,
        canceled_at=slots_reservations.canceled_at,
        offered=slots_reservations.offered
      FROM slots_reservations
      WHERE slots_reservations.slot_id = slots.id
    )

    remove_column :slots_reservations, :ex_start_at
    remove_column :slots_reservations, :ex_end_at
    remove_column :slots_reservations, :canceled_at
    remove_column :slots_reservations, :offered
  end
end