Add if/unless support to associations.

Author: beauby

lib/active_model/serializer/associations.rb

@@ -91,6 +91,7 @@ def associations(include_tree = DEFAULT_INCLUDE_TREE)
         Enumerator.new do |y|
           self.class._reflections.each do |reflection|
             key = reflection.options.fetch(:key, reflection.name)
+            next unless reflection.include?(self)
             next unless include_tree.key?(key)
             y.yield reflection.build_association(self, instance_options)
           end

lib/active_model/serializer/reflection.rb

@@ -25,7 +25,20 @@ class Serializer
     #
     # So you can inspect reflections in your Adapters.
     #
-    Reflection = Struct.new(:name, :options, :block) do
+    Reflection = Struct.new(:name, :options, :block, :condition_type, :condition) do
+      def initialize(name, options, block = nil)
+        super(name, options, block)
+        self.condition_type =
+          if options.key?(:if)
+            :if
+          elsif options.key?(:unless)
+            :unless
+          else
+            :none
+          end
+        self.condition = options[condition_type]
+      end
+
       # @api private
       def value(instance)
         if block
@@ -35,6 +48,18 @@ def value(instance)
         end
       end
 
+      # @api private
+      def include?(serializer)
+        case condition_type
+        when :if
+          serializer.send(condition)
+        when :unless
+          !serializer.send(condition)
+        else
+          true
+        end
+      end
+
       # Build association. This method is used internally to
       # build serializer's association by its reflection.
       #