From 6860318133a1d5b1f61d4c51bc3c7d0b4a3f8205 Mon Sep 17 00:00:00 2001
From: Lucas Hosseini <lucas.hosseini@gmail.com>
Date: Wed, 30 Dec 2015 17:25:41 +0100
Subject: [PATCH] Add support for if/unless on associations.

---
 CHANGELOG.md                                |  1 +
 lib/active_model/serializer/associations.rb |  1 +
 lib/active_model/serializer/reflection.rb   | 26 +++++++++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5f8bd834..a89c9e05 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ Breaking changes:
 
 Features:
 
+- [#1403](https://github.com/rails-api/active_model_serializers/pull/1403) Add support for if/unless on attributes/associations (@beauby)
 - [#1248](https://github.com/rails-api/active_model_serializers/pull/1248) Experimental: Add support for JSON API deserialization (@beauby)
 - [#1378](https://github.com/rails-api/active_model_serializers/pull/1378) Change association blocks
   to be evaluated in *serializer* scope, rather than *association* scope. (@bf4)
diff --git a/lib/active_model/serializer/associations.rb b/lib/active_model/serializer/associations.rb
index 42e872ce..fe4bfe1f 100644
--- a/lib/active_model/serializer/associations.rb
+++ b/lib/active_model/serializer/associations.rb
@@ -88,6 +88,7 @@ module ActiveModel
 
         Enumerator.new do |y|
           self.class._reflections.each do |reflection|
+            next unless reflection.included?(self)
             key = reflection.options.fetch(:key, reflection.name)
             next unless include_tree.key?(key)
             y.yield reflection.build_association(self, instance_options)
diff --git a/lib/active_model/serializer/reflection.rb b/lib/active_model/serializer/reflection.rb
index 19eb78b8..484b95ae 100644
--- a/lib/active_model/serializer/reflection.rb
+++ b/lib/active_model/serializer/reflection.rb
@@ -35,6 +35,18 @@ module ActiveModel
         end
       end
 
+      # @api private
+      def included?(serializer)
+        case condition_type
+        when :if
+          serializer.public_send(condition)
+        when :unless
+          !serializer.public_send(condition)
+        else
+          true
+        end
+      end
+
       # Build association. This method is used internally to
       # build serializer's association by its reflection.
       #
@@ -79,6 +91,20 @@ module ActiveModel
 
       private
 
+      def condition_type
+        if options.key?(:if)
+          :if
+        elsif options.key?(:unless)
+          :unless
+        else
+          :none
+        end
+      end
+
+      def condition
+        options[condition_type]
+      end
+
       def serializer_options(subject, parent_serializer_options, reflection_options)
         serializer = reflection_options.fetch(:serializer, nil)