Prevent loading association when include_data is set to false (#1710)

This should fix #1707.

CHANGELOG.md

@@ -7,6 +7,8 @@ Breaking changes:
 Features:
 
 Fixes:
+- [#1710](https://github.com/rails-api/active_model_serializers/pull/1710) Prevent association loading when `include_data` option
+  is set to `false`. (@groyoh)
 
 Misc:
 - [#1734](https://github.com/rails-api/active_model_serializers/pull/1734) Adds documentation for conditional attribute (@lambda2)

lib/active_model/serializer/reflection.rb

@@ -75,10 +75,10 @@ module ActiveModel
 
         if block
           block_value = instance_exec(serializer, &block)
-          if block_value == :nil
-            serializer.read_attribute_for_serialization(name)
-          else
+          if block_value != :nil
             block_value
+          elsif @_include_data
+            serializer.read_attribute_for_serialization(name)
           end
         else
           serializer.read_attribute_for_serialization(name)

test/adapter/json_api/relationships_test.rb

@@ -5,7 +5,8 @@ module ActiveModel
     module Adapter
       class JsonApi
         class RelationshipTest < ActiveSupport::TestCase
-          RelationshipAuthor = Class.new(::Model)
+          class RelationshipAuthor < ::Model; end
+
           class RelationshipAuthorSerializer < ActiveModel::Serializer
             has_one :bio do
               link :self, '//example.com/link_author/relationships/bio'
@@ -71,7 +72,6 @@ module ActiveModel
 
           def setup
             @post = Post.new(id: 1337, comments: [], author: nil)
-            @blog = Blog.new(id: 1337, name: 'extra')
             @bio = Bio.new(id: 1337)
             @like = Like.new(id: 1337)
             @role = Role.new(id: 'from-record')
@@ -82,7 +82,6 @@ module ActiveModel
             @author = RelationshipAuthor.new(
               id: 1337,
               posts: [@post],
-              blog: @blog,
               reviewer: @reviewer,
               bio: @bio,
               likes: [@like],
@@ -158,11 +157,17 @@ module ActiveModel
           end
 
           def test_relationship_not_including_data
+            @author.define_singleton_method(:read_attribute_for_serialization) do |attr|
+              fail 'should not be called' if attr == :blog
+              super(attr)
+            end
             expected = {
               links: { self: '//example.com/link_author/relationships/blog' }
             }
+            assert_nothing_raised do
               assert_relationship(:blog, expected)
             end
+          end
 
           def test_relationship_including_data_explicit
             expected = {