:only/:except options for expose

[ka8725]

These options are useful to specify exposed fields for a using entity per request:

class User < GE
  expose :name
  expose :email
  expose :age
end

class Responce1 < GE
  expose :users, using: User, only: :name
end

class Respose2 < GE 
  expose :users, using: User, except: :email
end

class Respose3 < GE 
  expose :users, using: User, except: :name
end

As the result we have one shared type (User) that can be used in different context that need only specific fields from that type.

[dchandekstark]

Isn't this feature essentially already available? https://github.com/ruby-grape/grape-entity#returning-only-the-fields-you-want

[ka8725]

@dchandekstark I don't think so. The reference you pointed is about evaluating (or data processing) step. But this PR is about types definition and use it with inheritance.

[ka8725]

Actually, this PR is not essential. On the project we've come up with the following base class:

# Example:
#
#   module Map
#     class UsersLocationsResponseSerializer < ApplicationSerializer
#       # Array of Hashes with Symbol keys that's response of Queries::Map::LastLocations
#       expose :locations, using: LocationSerializer
#       # Array of Hashes with Symbol keys that's response of Queries::Map::LastActivities
#       expose_nested :activities do
#         expose :user_id
#         expose_time :last_client_activity
#       end
#       # Array of Task
#       expose :tasks, using: TaskSerializer, only: %i[id summary]
#       # Array of User
#       expose :users, using: UserSerializer, except: %i[email]
#       # Boolean, true means the map should be fully redrawn (significant changes since last request)
#       expose :clear
#     end
#   end
class ApplicationSerializer < Grape::Entity
  # Extends the standard functionality with `:only` and `:except` options that
  # define exact serializable fields for the nested structures specified with `:using`.
  #
  # @note The `:only` and `:except` options can be used only along with `:using`.
  # @see Grape::Entity.expose for the standard set of attributes.
  def self.expose(*attributes, only: nil, except: nil, **options)
    if only || except
      using_class = options.delete(:using)
      raise ArgumentError, ':only or :except options can be used only with :using' unless using_class

      expose(*attributes, **options, format_with: proc { using_class.represent(_1, only: only, except: except) })
    else
      super(*attributes, **options)
    end
  end

  # Defines _in-line_ serializers.
  def self.expose_nested(attribute, **options, &block)
    entity_class = Class.new(ApplicationSerializer, &block)
    const_set("#{name.demodulize}_#{attribute}", entity_class)
    expose(attribute, using: entity_class, **options, &block)
  end
end