Problems exposing has_and_belongs_to_many relation using Grape::Entity

Question

i have Trip model which has destinations defined like that:

class Trip < ActiveRecord::Base
    ...
    has_and_belongs_to_many :destinations, join_table: :trips_destinations
    ...
end

What I want to do is to expose the trip information included the associated destinations. I defined this response entity for the destinations:

module Services
  module Trips
    class DestinationResponseEntity < Grape::Entity
      expose :id
      expose :name
    end
  end
end

And the trip destination entity is this:

module Services
  module Trips
    class TripResponseEntity < Grape::Entity
      expose :id
      expose :title
      expose :duration
      expose :total_price
      expose :description
      expose :destinations, using: Trips::DestinationResponseEntity
      expose :photo
    end
  end
end

I'm presenting the result in that way:

  present trip, :with => Trips::TripResponseEntity

But the response of the service returns always an empty destination array.

[{"id":3,"title":"Islandhopping in Thailand","duration":14,"total_price":3450,"description":"Relax under swaying palm trees then jump into crystal-clear waters",**"destinations":[]**,"photo":"http://s3.amazonaws.com/ntradadevelopment/images/trips/3/original/thailand.jpeg"]

In the console I can see all the destinations associated with the trip properly. Any clue of what could be causing the issue is really appreciated.

Answer 1

What you're doing with Grape::Entity looks correct to me.

I encountered a similar issue that turned out to be a problem with my has_and_belongs_to_many relationship not being defined correctly so you might need to check that again.

In particular, you seem to be overriding the default naming convention of the join table. Could it be tripping up Grape?