Custom action using manage_relationship when relationship is many_to_many

Resources involved are Employee, Shift, and EmployeeShift

Employee and shift are related many_to_many, through EmployeeShift, however, since an employee can clock in and out multiple times during an shift EmployeeShift has it’s own id and isn’t unique by pairs of Employee and Shift ids:

  attributes do
    uuid_primary_key :id
    attribute :in_at, :utc_datetime_usec, allow_nil?: false
    attribute :out_at, :utc_datetime_usec

    create_timestamp :created_at
    update_timestamp :updated_at
  end

  relationships do
    belongs_to :employee, PointOfSale.Accounts.Employee do
      api PointOfSale.Accounts
      allow_nil? false
      attribute_writable? true
    end

    belongs_to :shift, PointOfSale.Stores.Shift do
      allow_nil? false
      attribute_writable? true
    end
  end

Additionally EmployeeShifts have a custom primary create action called start that takes arguments of employ_id and shift_id and set’s the start time:

create :start do
      primary? true
      accept [:employee_id, :shift_id]

      argument :employee_id, :uuid, allow_nil?: false
      argument :shift_id, :uuid, allow_nil?: false

      change set_attribute(:in_at, DateTime.utc_now())
      change set_attribute(:employee_id, arg(:employee_id))
      change set_attribute(:shift_id, arg(:shift_id))
    end

When I start a new Shift I want to be able to pass an array of Employee ids to manage_relationship so that the custom start create function is called on EmployeeShift so that the included employees are clocked in automatically as the shift starts:

Shift

    has_many :employee_shifts, PointOfSale.Stores.EmployeeShift

    many_to_many :employees, PointOfSale.Accounts.Employee do
      api PointOfSale.Accounts
      through PointOfSale.Stores.EmployeeShift
      join_relationship :employee_shifts
    end

create :start do
      accept [:till_id, :employee_ids]

      argument :till_id, :uuid, allow_nil?: false
      argument :employee_ids, {:array, :uuid}, allow_nil?: false

      change set_attribute(:start_at, DateTime.utc_now())
      change set_attribute(:till_id, arg(:till_id))
      change manage_relationship(:employee_ids, :employee_shifts, type: create)
    end

However, when I attempt to create a new Shift via this action I get an error saying that the required arguments of shift_id and employee_id for EmployeeShift are missing.

The shift_id should come from the shift that is created just before running the manage relationship. And I thought I would be accepting employee_ids via the manage_relationship function.

I see that I can pass a map instead of a list of ids, and maybe that is the way, but that doesn’t solve the passing in of the shift_id that I don’t have since it get’s created.