[Feat] Improve select to take third parameter

This makes `select` to behave better based on the kind of the attribute.
When `select` is not overridden, we don't call it anymore.
We check the arity of `select` at the definition step, so there
should be no performance penalty other than calling cost.

Author: okuramasafumi

README.md

@@ -840,7 +840,7 @@ To filter attributes, you can use `select` instance method. Using `attributes` i
 
 #### Filtering attributes with `select`
 
-`select` takes two parameters, the name of an attribute and the value of an attribute. If it returns false that attribute is rejected.
+`select` takes two or three parameters, the name of an attribute, the value of an attribute and the attribute object (`Alba::Association`, for example). If it returns false that attribute is rejected.
 
 ```ruby
 class Foo
@@ -863,6 +863,9 @@ class RestrictedFooResource < GenericFooResource
   def select(_key, value)
     !value.nil?
   end
+
+  # This is also possible
+  # def select(_key, _value, _attribute)
 end
 
 foo = Foo.new(1, nil, 'body')

lib/alba/resource.rb

@@ -14,7 +14,7 @@ module Alba
   module Resource
     # @!parse include InstanceMethods
     # @!parse extend ClassMethods
-    INTERNAL_VARIABLES = {_attributes: {}, _key: nil, _key_for_collection: nil, _meta: nil, _transform_type: :none, _transforming_root_key: false, _key_transformation_cascade: true, _on_error: nil, _on_nil: nil, _layout: nil, _collection_key: nil, _helper: nil, _resource_methods: []}.freeze # rubocop:disable Layout/LineLength
+    INTERNAL_VARIABLES = {_attributes: {}, _key: nil, _key_for_collection: nil, _meta: nil, _transform_type: :none, _transforming_root_key: false, _key_transformation_cascade: true, _on_error: nil, _on_nil: nil, _layout: nil, _collection_key: nil, _helper: nil, _resource_methods: [], _select_arity: nil}.freeze # rubocop:disable Layout/LineLength
     private_constant :INTERNAL_VARIABLES
 
     WITHIN_DEFAULT = Object.new.freeze
@@ -225,14 +225,20 @@ def attributes
 
       # Default implementation for selecting attributes
       # Override this method to filter attributes based on key and value
-      def select(_key, _value)
+      def select(_key, _value, _attribute)
         true
       end
 
       def set_key_and_attribute_body_from(obj, key, attribute, hash)
         key = transform_key(key)
         value = fetch_attribute(obj, key, attribute)
-        return unless select(key, value)
+        # When `select` is not overridden, skip calling it for better performance
+        unless @_select_arity.nil?
+          # `select` can be overridden with both 2 and 3 parameters
+          # Here we check the arity and build arguments accordingly
+          args = @_select_arity == 3 ? [key, value, attribute] : [key, value]
+          return unless select(*args)
+        end
 
         hash[key] = value unless Alba::REMOVE_KEY == value # rubocop:disable Style/YodaCondition
       end
@@ -332,6 +338,8 @@ def method_added(method_name) # rubocop:disable Metrics/MethodLength
           alias_method :to_h, :deprecated_serializable_hash
         when :attributes
           warn 'Overriding `attributes` is deprecated, use `select` instead.', category: :deprecated, uplevel: 1
+        when :select
+          @_select_arity = instance_method(:select).arity
         when :_setup # noop
         else
           _resource_methods << method_name.to_sym

test/usecases/nil_filtering_test.rb

@@ -4,14 +4,12 @@
 
 class NilFilteringTest < Minitest::Test
   class User
-    attr_accessor :id, :name, :email, :created_at, :updated_at
+    attr_accessor :id, :name, :email, :parent_user
 
     def initialize(id, name, email)
       @id = id
       @name = name
       @email = email
-      @created_at = Time.now
-      @updated_at = Time.now
     end
   end
 
@@ -35,4 +33,51 @@ def test_it_filters_nil_attributes_with_select
       UserResource.new(@user).serialize
     )
   end
+
+  class UserResource2 < UserResource
+    def select(_key, _value, _attribute)
+      true
+    end
+  end
+
+  def test_it_filters_with_select_with_three_parameters
+    assert_equal(
+      '{"id":1,"name":null,"email":null}',
+      UserResource2.new(@user).serialize
+    )
+  end
+
+  class UserResourceWithAssociation
+    include Alba::Resource
+
+    attributes :id, :name, :email
+
+    one :parent_user do
+      attributes :id, :name, :email
+    end
+  end
+
+  class UserResourceWithAssociationFilteringIt < UserResourceWithAssociation
+    def select(_key, _value, attribute)
+      !attribute.is_a?(Alba::Association)
+    end
+  end
+
+  class UserResourceWithAssociationOnlySelectingIt < UserResourceWithAssociation
+    def select(_key, _value, attribute)
+      attribute.is_a?(Alba::Association)
+    end
+  end
+
+  def test_it_filters_with_select_with_attribute_parameter
+    @user.parent_user = User.new(2, nil, nil)
+    assert_equal(
+      '{"id":1,"name":null,"email":null}',
+      UserResourceWithAssociationFilteringIt.new(@user).serialize
+    )
+    assert_equal(
+      '{"parent_user":{"id":2,"name":null,"email":null}}',
+      UserResourceWithAssociationOnlySelectingIt.new(@user).serialize
+    )
+  end
 end