String/Lambda support for conditional attributes/associations

CHANGELOG.md

@@ -6,6 +6,7 @@ Breaking changes:
 - [#1662](https://github.com/rails-api/active_model_serializers/pull/1662) Drop support for Rails 4.0 and Ruby 2.0.0. (@remear)
 
 Features:
+- [#1699](https://github.com/rails-api/active_model_serializers/pull/1699) String/Lambda support for conditional attributes/associations (@mtsmfm)
 - [#1687](https://github.com/rails-api/active_model_serializers/pull/1687) Only calculate `_cache_digest` (in `cache_key`) when `skip_digest` is false. (@bf4)
 - [#1647](https://github.com/rails-api/active_model_serializers/pull/1647) Restrict usage of `serializable_hash` options
   to the ActiveModel::Serialization and ActiveModel::Serializers::JSON interface. (@bf4)

docs/general/serializers.md

@@ -80,6 +80,10 @@ end
 
 ```ruby
 has_one :blog, if: :show_blog?
+# you can also use a string or lambda
+# has_one :blog, if: 'scope.admin?'
+# has_one :blog, if: -> (serializer) { serializer.scope.admin? }
+# has_one :blog, if: -> { scope.admin? }
 
 def show_blog?
   scope.admin?

lib/active_model/serializer/field.rb

@@ -4,6 +4,12 @@ module ActiveModel
     # specified in the ActiveModel::Serializer class.
     # Notice that the field block is evaluated in the context of the serializer.
     Field = Struct.new(:name, :options, :block) do
+      def initialize(*)
+        super
+
+        validate_condition!
+      end
+
       # Compute the actual value of a field for a given serializer instance.
       # @param [Serializer] The serializer instance for which the value is computed.
       # @return [Object] value
@@ -27,9 +33,9 @@ module ActiveModel
       def excluded?(serializer)
         case condition_type
         when :if
-          !serializer.public_send(condition)
+          !evaluate_condition(serializer)
         when :unless
-          serializer.public_send(condition)
+          evaluate_condition(serializer)
         else
           false
         end
@@ -37,6 +43,34 @@ module ActiveModel
 
       private
 
+      def validate_condition!
+        return if condition_type == :none
+
+        case condition
+        when Symbol, String, Proc
+          # noop
+        else
+          fail TypeError, "#{condition_type.inspect} should be a Symbol, String or Proc"
+        end
+      end
+
+      def evaluate_condition(serializer)
+        case condition
+        when Symbol
+          serializer.public_send(condition)
+        when String
+          serializer.instance_eval(condition)
+        when Proc
+          if condition.arity.zero?
+            serializer.instance_exec(&condition)
+          else
+            serializer.instance_exec(serializer, &condition)
+          end
+        else
+          nil
+        end
+      end
+
       def condition_type
         @condition_type ||=
           if options.key?(:if)

test/serializers/associations_test.rb

@@ -239,27 +239,55 @@ module ActiveModel
           end
         end
 
+        # rubocop:disable Metrics/AbcSize
         def test_conditional_associations
-          serializer = Class.new(ActiveModel::Serializer) do
-            belongs_to :if_assoc_included, if: :true
-            belongs_to :if_assoc_excluded, if: :false
-            belongs_to :unless_assoc_included, unless: :false
-            belongs_to :unless_assoc_excluded, unless: :true
+          model = ::Model.new(true: true, false: false)
 
-            def true
-              true
+          scenarios = [
+            { options: { if:     :true  }, included: true  },
+            { options: { if:     :false }, included: false },
+            { options: { unless: :false }, included: true  },
+            { options: { unless: :true  }, included: false },
+            { options: { if:     'object.true'  }, included: true  },
+            { options: { if:     'object.false' }, included: false },
+            { options: { unless: 'object.false' }, included: true  },
+            { options: { unless: 'object.true'  }, included: false },
+            { options: { if:     -> { object.true }  }, included: true  },
+            { options: { if:     -> { object.false } }, included: false },
+            { options: { unless: -> { object.false } }, included: true  },
+            { options: { unless: -> { object.true }  }, included: false },
+            { options: { if:     -> (s) { s.object.true }  }, included: true  },
+            { options: { if:     -> (s) { s.object.false } }, included: false },
+            { options: { unless: -> (s) { s.object.false } }, included: true  },
+            { options: { unless: -> (s) { s.object.true }  }, included: false }
+          ]
+
+          scenarios.each do |s|
+            serializer = Class.new(ActiveModel::Serializer) do
+              belongs_to :association, s[:options]
+
+              def true
+                true
+              end
+
+              def false
+                false
+              end
             end
 
-            def false
-              false
+            hash = serializable(model, serializer: serializer).serializable_hash
+            assert_equal(s[:included], hash.key?(:association), "Error with #{s[:options]}")
+          end
+        end
+
+        def test_illegal_conditional_associations
+          exception = assert_raises(TypeError) do
+            Class.new(ActiveModel::Serializer) do
+              belongs_to :x, if: nil
             end
           end
 
-          model = ::Model.new
-          hash = serializable(model, serializer: serializer).serializable_hash
-          expected = { if_assoc_included: nil, unless_assoc_included: nil }
-
-          assert_equal(expected, hash)
+          assert_match(/:if should be a Symbol, String or Proc/, exception.message)
         end
       end
     end

test/serializers/attribute_test.rb

@@ -96,27 +96,55 @@ module ActiveModel
         assert_equal(expected, hash)
       end
 
-      def test_conditional_attributes
-        serializer = Class.new(ActiveModel::Serializer) do
-          attribute :if_attribute_included, if: :true
-          attribute :if_attribute_excluded, if: :false
-          attribute :unless_attribute_included, unless: :false
-          attribute :unless_attribute_excluded, unless: :true
+      # rubocop:disable Metrics/AbcSize
+      def test_conditional_associations
+        model = ::Model.new(true: true, false: false)
 
-          def true
-            true
+        scenarios = [
+          { options: { if:     :true  }, included: true  },
+          { options: { if:     :false }, included: false },
+          { options: { unless: :false }, included: true  },
+          { options: { unless: :true  }, included: false },
+          { options: { if:     'object.true'  }, included: true  },
+          { options: { if:     'object.false' }, included: false },
+          { options: { unless: 'object.false' }, included: true  },
+          { options: { unless: 'object.true'  }, included: false },
+          { options: { if:     -> { object.true }  }, included: true  },
+          { options: { if:     -> { object.false } }, included: false },
+          { options: { unless: -> { object.false } }, included: true  },
+          { options: { unless: -> { object.true }  }, included: false },
+          { options: { if:     -> (s) { s.object.true }  }, included: true  },
+          { options: { if:     -> (s) { s.object.false } }, included: false },
+          { options: { unless: -> (s) { s.object.false } }, included: true  },
+          { options: { unless: -> (s) { s.object.true }  }, included: false }
+        ]
+
+        scenarios.each do |s|
+          serializer = Class.new(ActiveModel::Serializer) do
+            attribute :attribute, s[:options]
+
+            def true
+              true
+            end
+
+            def false
+              false
+            end
           end
 
-          def false
-            false
+          hash = serializable(model, serializer: serializer).serializable_hash
+          assert_equal(s[:included], hash.key?(:attribute), "Error with #{s[:options]}")
+        end
+      end
+
+      def test_illegal_conditional_attributes
+        exception = assert_raises(TypeError) do
+          Class.new(ActiveModel::Serializer) do
+            attribute :x, if: nil
           end
         end
 
-        model = ::Model.new
-        hash = serializable(model, serializer: serializer).serializable_hash
-        expected = { if_attribute_included: nil, unless_attribute_included: nil }
-
-        assert_equal(expected, hash)
+        assert_match(/:if should be a Symbol, String or Proc/, exception.message)
       end
     end
   end