ActiveModel support for the :include serialization option

This commit moves support for the :include serialization option for
serializing associated objects out of ActiveRecord in into ActiveModel.
The following methods support the :include option:

  * serializable_hash
  * to_json
  * to_xml

Instances must respond to methods named by the values of the :includes
array (or keys of the :includes hash). If an association method returns
an object that is_a?(Enumerable) (which AR has_many associations do), it
is assumed to be a collection association, and its elements must respond
to :serializable_hash. Otherwise it must respond to :serializable_hash
itself.

While here, fix #858, XmlSerializer should not singularize already
singular association names.

6 files changed, 190 insertions, 90 deletions

diff --git a/activemodel/lib/active_model/serialization.rb b/activemodel/lib/active_model/serialization.rb
index 0b4067257e..9260c5082d 100644
--- a/activemodel/lib/active_model/serialization.rb
+++ b/activemodel/lib/active_model/serialization.rb
@@ -77,7 +77,38 @@ module ActiveModel
       end
 
       method_names = Array.wrap(options[:methods]).select { |n| respond_to?(n) }
-      Hash[(attribute_names + method_names).map { |n| [n, send(n)] }]
+      hash = Hash[(attribute_names + method_names).map { |n| [n, send(n)] }]
+
+      serializable_add_includes(options) do |association, records, opts|
+        hash[association] = if records.is_a?(Enumerable)
+          records.map { |a| a.serializable_hash(opts) }
+        else
+          records.serializable_hash(opts)
+        end
+      end
+
+      hash
     end
+
+    private
+      # Add associations specified via the <tt>:include</tt> option.
+      #
+      # Expects a block that takes as arguments:
+      #   +association+ - name of the association
+      #   +records+     - the association record(s) to be serialized
+      #   +opts+        - options for the association records
+      def serializable_add_includes(options = {})
+        return unless include = options[:include]
+
+        unless include.is_a?(Hash)
+          include = Hash[Array.wrap(include).map { |n| [n, {}] }]
+        end
+
+        include.each do |association, opts|
+          if records = send(association)
+            yield association, records, opts
+          end
+        end
+      end
   end
 end
diff --git a/activemodel/lib/active_model/serializers/xml.rb b/activemodel/lib/active_model/serializers/xml.rb
index 9812af43d6..64dda3bcee 100644
--- a/activemodel/lib/active_model/serializers/xml.rb
+++ b/activemodel/lib/active_model/serializers/xml.rb
@@ -101,6 +101,7 @@ module ActiveModel
 
           @builder.tag!(*args) do
             add_attributes_and_methods
+            add_includes
             add_extra_behavior
             add_procs
             yield @builder if block_given?
@@ -120,6 +121,45 @@ module ActiveModel
           end
         end
 
+        def add_includes
+          @serializable.send(:serializable_add_includes, options) do |association, records, opts|
+            add_associations(association, records, opts)
+          end
+        end
+
+        # TODO This can likely be cleaned up to simple use ActiveSupport::XmlMini.to_tag as well.
+        def add_associations(association, records, opts)
+          merged_options = opts.merge(options.slice(:builder, :indent))
+          merged_options[:skip_instruct] = true
+
+          if records.is_a?(Enumerable)
+            tag  = ActiveSupport::XmlMini.rename_key(association.to_s, options)
+            type = options[:skip_types] ? { } : {:type => "array"}
+            association_name = association.to_s.singularize
+            merged_options[:root] = association_name
+
+            if records.empty?
+              @builder.tag!(tag, type)
+            else
+              @builder.tag!(tag, type) do
+                records.each do |record|
+                  if options[:skip_types]
+                    record_type = {}
+                  else
+                    record_class = (record.class.to_s.underscore == association_name) ? nil : record.class.name
+                    record_type = {:type => record_class}
+                  end
+
+                  record.to_xml merged_options.merge(record_type)
+                end
+              end
+            end
+          else
+            merged_options[:root] = association.to_s
+            records.to_xml(merged_options)
+          end
+        end
+
         def add_procs
           if procs = options.delete(:procs)
             Array.wrap(procs).each do |proc|
diff --git a/activemodel/test/cases/serialization_test.rb b/activemodel/test/cases/serialization_test.rb
index 10cb600e7b..5122f08eec 100644
--- a/activemodel/test/cases/serialization_test.rb
+++ b/activemodel/test/cases/serialization_test.rb
@@ -1,13 +1,19 @@
 require "cases/helper"
+require 'active_support/core_ext/object/instance_variables'
 
 class SerializationTest < ActiveModel::TestCase
   class User
     include ActiveModel::Serialization
 
-    attr_accessor :name, :email, :gender
+    attr_accessor :name, :email, :gender, :address, :friends
+
+    def initialize(name, email, gender)
+      @name, @email, @gender = name, email, gender
+      @friends = []
+    end
 
     def attributes
-      @attributes ||= {'name' => 'nil', 'email' => 'nil', 'gender' => 'nil'}
+      instance_values.except("address", "friends")
     end
 
     def foo
@@ -15,11 +21,25 @@ class SerializationTest < ActiveModel::TestCase
     end
   end
 
+  class Address
+    include ActiveModel::Serialization
+
+    attr_accessor :street, :city, :state, :zip
+
+    def attributes
+      instance_values
+    end
+  end
+
   setup do
-    @user = User.new
-    @user.name = 'David'
-    @user.email = 'david@example.com'
-    @user.gender = 'male'
+    @user = User.new('David', 'david@example.com', 'male')
+    @user.address = Address.new
+    @user.address.street = "123 Lane"
+    @user.address.city = "Springfield"
+    @user.address.state = "CA"
+    @user.address.zip = 11111
+    @user.friends = [User.new('Joe', 'joe@example.com', 'male'),
+                     User.new('Sue', 'sue@example.com', 'female')]
   end
 
   def test_method_serializable_hash_should_work
@@ -57,4 +77,45 @@ class SerializationTest < ActiveModel::TestCase
     assert_equal expected , @user.serializable_hash(:methods => [:bar])
   end
 
+  def test_include_option_with_singular_association
+    expected =  {"name"=>"David", "gender"=>"male", "email"=>"david@example.com",
+                 :address=>{"street"=>"123 Lane", "city"=>"Springfield", "state"=>"CA", "zip"=>11111}}
+    assert_equal expected , @user.serializable_hash(:include => :address)
+  end
+
+  def test_include_option_with_plural_association
+    expected =  {"email"=>"david@example.com", "gender"=>"male", "name"=>"David",
+                 :friends=>[{"name"=>'Joe', "email"=>'joe@example.com', "gender"=>'male'},
+                            {"name"=>'Sue', "email"=>'sue@example.com', "gender"=>'female'}]}
+    assert_equal expected , @user.serializable_hash(:include => :friends)
+  end
+
+  def test_include_option_with_empty_association
+    @user.friends = []
+    expected =  {"email"=>"david@example.com", "gender"=>"male", "name"=>"David", :friends=>[]}
+    assert_equal expected , @user.serializable_hash(:include => :friends)
+  end
+
+  def test_multiple_includes
+    expected =  {"email"=>"david@example.com", "gender"=>"male", "name"=>"David",
+                 :address=>{"street"=>"123 Lane", "city"=>"Springfield", "state"=>"CA", "zip"=>11111},
+                 :friends=>[{"name"=>'Joe', "email"=>'joe@example.com', "gender"=>'male'},
+                            {"name"=>'Sue', "email"=>'sue@example.com', "gender"=>'female'}]}
+    assert_equal expected , @user.serializable_hash(:include => [:address, :friends])
+  end
+
+  def test_include_with_options
+    expected =  {"email"=>"david@example.com", "gender"=>"male", "name"=>"David",
+                 :address=>{"street"=>"123 Lane"}}
+    assert_equal expected , @user.serializable_hash(:include => {:address => {:only => "street"}})
+  end
+
+  def test_nested_include
+    @user.friends.first.friends = [@user]
+    expected =  {"email"=>"david@example.com", "gender"=>"male", "name"=>"David",
+                 :friends=>[{"name"=>'Joe', "email"=>'joe@example.com', "gender"=>'male',
+                             :friends => ["email"=>"david@example.com", "gender"=>"male", "name"=>"David"]},
+                            {"name"=>'Sue', "email"=>'sue@example.com', "gender"=>'female', :friends => []}]}
+    assert_equal expected , @user.serializable_hash(:include => {:friends => {:include => :friends}})
+  end
 end
diff --git a/activemodel/test/cases/serializers/xml_serialization_test.rb b/activemodel/test/cases/serializers/xml_serialization_test.rb
index f978191d22..a38ef8e223 100644
--- a/activemodel/test/cases/serializers/xml_serialization_test.rb
+++ b/activemodel/test/cases/serializers/xml_serialization_test.rb
@@ -7,9 +7,11 @@ class Contact
   extend ActiveModel::Naming
   include ActiveModel::Serializers::Xml
 
+  attr_accessor :address, :friends
+
   def attributes
-    instance_values
-  end unless method_defined?(:attributes)
+    instance_values.except("address", "friends")
+  end
 end
 
 module Admin
@@ -20,6 +22,17 @@ end
 class Customer < Struct.new(:name)
 end
 
+class Address
+  extend ActiveModel::Naming
+  include ActiveModel::Serializers::Xml
+
+  attr_accessor :street, :city, :state, :zip
+
+  def attributes
+    instance_values
+  end
+end
+
 class XmlSerializationTest < ActiveModel::TestCase
   def setup
     @contact = Contact.new
@@ -30,6 +43,12 @@ class XmlSerializationTest < ActiveModel::TestCase
     customer = Customer.new
     customer.name = "John"
     @contact.preferences = customer
+    @contact.address = Address.new
+    @contact.address.street = "123 Lane"
+    @contact.address.city = "Springfield"
+    @contact.address.state = "CA"
+    @contact.address.zip = 11111
+    @contact.friends = [Contact.new, Contact.new]
   end
 
   test "should serialize default root" do
@@ -138,4 +157,33 @@ class XmlSerializationTest < ActiveModel::TestCase
     assert_match %r{<contact type="Contact">}, xml
     assert_match %r{<name>aaron stack</name>}, xml
   end
+
+  test "include option with singular association" do
+    xml = @contact.to_xml :include => :address, :indent => 0
+    assert xml.include?(@contact.address.to_xml(:indent => 0, :skip_instruct => true))
+  end
+
+  test "include option with plural association" do
+    xml = @contact.to_xml :include => :friends, :indent => 0
+    assert_match %r{<friends type="array">}, xml
+    assert_match %r{<friend type="Contact">}, xml
+  end
+
+  test "multiple includes" do
+    xml = @contact.to_xml :indent => 0, :skip_instruct => true, :include => [ :address, :friends ]
+    assert xml.include?(@contact.address.to_xml(:indent => 0, :skip_instruct => true))
+    assert_match %r{<friends type="array">}, xml
+    assert_match %r{<friend type="Contact">}, xml
+  end
+
+  test "include with options" do
+    xml = @contact.to_xml :indent  => 0, :skip_instruct => true, :include => { :address => { :only => :city } }
+    assert xml.include?(%(><address><city>Springfield</city></address>))
+  end
+
+  test "propagates skip_types option to included associations" do
+    xml = @contact.to_xml :include => :friends, :indent => 0, :skip_types => true
+    assert_match %r{<friends>}, xml
+    assert_match %r{<friend>}, xml
+  end
 end
diff --git a/activerecord/lib/active_record/serialization.rb b/activerecord/lib/active_record/serialization.rb
index e3185a9c5a..5ad40d8cd9 100644
--- a/activerecord/lib/active_record/serialization.rb
+++ b/activerecord/lib/active_record/serialization.rb
@@ -10,46 +10,8 @@ module ActiveRecord #:nodoc:
       options[:except] = Array.wrap(options[:except]).map { |n| n.to_s }
       options[:except] |= Array.wrap(self.class.inheritance_column)
 
-      hash = super(options)
-
-      serializable_add_includes(options) do |association, records, opts|
-        hash[association] = records.is_a?(Enumerable) ?
-          records.map { |r| r.serializable_hash(opts) } :
-          records.serializable_hash(opts)
-      end
-
-      hash
+      super(options)
     end
-
-    private
-      # Add associations specified via the <tt>:include</tt> option.
-      #
-      # Expects a block that takes as arguments:
-      #   +association+ - name of the association
-      #   +records+     - the association record(s) to be serialized
-      #   +opts+        - options for the association records
-      def serializable_add_includes(options = {})
-        return unless include_associations = options.delete(:include)
-
-        include_has_options = include_associations.is_a?(Hash)
-        associations = include_has_options ? include_associations.keys : Array.wrap(include_associations)
-
-        associations.each do |association|
-          records = case self.class.reflect_on_association(association).macro
-          when :has_many, :has_and_belongs_to_many
-            send(association).to_a
-          when :has_one, :belongs_to
-            send(association)
-          end
-
-          if records
-            association_options = include_has_options ? include_associations[association] : {}
-            yield(association, records, association_options)
-          end
-        end
-
-        options[:include] = include_associations
-      end
   end
 end
 
diff --git a/activerecord/lib/active_record/serializers/xml_serializer.rb b/activerecord/lib/active_record/serializers/xml_serializer.rb
index 67f6c7833c..cbfa1ad609 100644
--- a/activerecord/lib/active_record/serializers/xml_serializer.rb
+++ b/activerecord/lib/active_record/serializers/xml_serializer.rb
@@ -182,48 +182,6 @@ module ActiveRecord #:nodoc:
       options[:except] |= Array.wrap(@serializable.class.inheritance_column)
     end
 
-    def add_extra_behavior
-      add_includes
-    end
-
-    def add_includes
-      procs = options.delete(:procs)
-      @serializable.send(:serializable_add_includes, options) do |association, records, opts|
-        add_associations(association, records, opts)
-      end
-      options[:procs] = procs
-    end
-
-    # TODO This can likely be cleaned up to simple use ActiveSupport::XmlMini.to_tag as well.
-    def add_associations(association, records, opts)
-      association_name = association.to_s.singularize
-      merged_options   = options.merge(opts).merge!(:root => association_name, :skip_instruct => true)
-
-      if records.is_a?(Enumerable)
-        tag  = ActiveSupport::XmlMini.rename_key(association.to_s, options)
-        type = options[:skip_types] ? { } : {:type => "array"}
-
-        if records.empty?
-          @builder.tag!(tag, type)
-        else
-          @builder.tag!(tag, type) do
-            records.each do |record|
-              if options[:skip_types]
-                record_type = {}
-              else
-                record_class = (record.class.to_s.underscore == association_name) ? nil : record.class.name
-                record_type = {:type => record_class}
-              end
-
-              record.to_xml merged_options.merge(record_type)
-            end
-          end
-        end
-      else
-        records.to_xml(merged_options)
-      end
-    end
-
     class Attribute < ActiveModel::Serializers::Xml::Serializer::Attribute #:nodoc:
       def compute_type
         klass = @serializable.class