Best practice for creating a record in a nested route

[treagod]

Hello!

I just want to clarify what's the best way to create a record in a nested route. I didn't find any information in the documentation on this topic, so maybe it's worth to add it to the How-Tos? Anyway, I have two models and a schema (the one for the board does not matter here):

class Board < Marten::Model
  field :id, :big_int, primary_key: true, auto: true
  field :name, :string, max_size: 255
  
  with_timestamp_fields
end

class Column < Marten::Model
  field :id, :big_int, primary_key: true, auto: true
  field :name, :string, max_size: 255
  field :board, :many_to_one, to: Board, related: :columns

  with_timestamp_fields
end

class ColumnSchema < Marten::Schema
  field :name, :string, max_size: 255
  field :board_id, :int # Should this even be here in the schema?
end

I now have following path /boards/<board_pk:int>/columns/create. My solution is to add the Board to the context and add a hidden field to the form:

class Boards::Columns::CreateHandler < Marten::Handlers::RecordCreate
  template_name "boards/columns/create.html"
  model Column
  schema ColumnSchema

  before_dispatch :add_board_to_context

  def success_url
    reverse("boards:detail", pk: params["board_pk"])
  end

  private def add_board_to_context
    # I wanted to just add the board id here, but the id can't be added to the context because uint is not supported.
    # I then figured getting the associated model first would be beneficial for data consistency?
    context["board"] = Board.all.get!(id: params["board_pk"])
  end
end

<form...>
  <!-- rest of form -->
  <input type="hidden" name="{{schema.board_id.id}}" value="{{ board.pk }}">
  <!-- rest of form -->
</form>

Is there another way? One I also had on my mind was to use the before_schema_validation callback and assign the board_id there. I didn't like that approach, because I would have to create a setter for this schema field.

Happy to hear about other solutions. And if this is really not yet in the documentation, it would be worth considering expanding it!

[ellmetha]

Hey! 👋

It really depends on the situation and what you are trying to achieve!

I think the solution involving a board_id schema field would be necessary in situations where the form needs to display a list of boards to select from (with a select input for example). If the board is inferred from the route and can't be selected, then I would opt for a solution that does not involve adding a schema field and that does not involve using a hidden input (since the value of such inputs can technically be overridden by end users). Using Marten::Handlers::Schema instead of Marten::Handlers::RecordCreate could work in this light:

class Boards::Columns::CreateHandler < Marten::Handlers::Schema
  template_name "boards/columns/create.html"
  schema ColumnSchema

  after_successful_schema_validation :create_column

  def success_url
    reverse("boards:detail", pk: params["board_pk"])
  end

  private def create_column
    column = Column.new(schema.validated_data)
    column.board = Board.all.get!(id: params["board_pk"])
    column.save!
  end
end

Otherwise, if you still want to use Marten::Handlers::RecordCreate you could also override #process_valid_schema as follows:

class Boards::Columns::CreateHandler < Marten::Handlers::RecordCreate
  template_name "boards/columns/create.html"
  model Column
  schema ColumnSchema

  def success_url
    reverse("boards:detail", pk: params["board_pk"])
  end

  def process_valid_schema
    column = Column.new(schema.validated_data)
    column.board = Board.all.get!(id: params["board_pk"])
    column.save!

    super
  end
end

Those are the cleanest solutions I think.

Presently, Marten::Handlers::RecordCreate does not help much if the new record's initialization logic must be customized. We could improve this easily though by introducing dedicated methods in the Marten::Handlers::RecordCreate class.

[treagod]

Sounds reasonable to me! Do you agree that this might be helpful to include into the documentation?

Nested routes occur again and again, so I think this would be helpful especially for newcomers

[ellmetha]

Yes, I guess we could add a how-to guide on how to perform common customizations with generic handlers. 👍