Add support for nested relationships for the json adapter

initial refactor to make way for easy feature adding

refactored a bit more, and matched some method names to that of json_api

rename add_relationship methods to be less awkward

tests added

all tests tpass

remove binding.pry require

fixed app warnings

removed unused method

changed restrict_to to nested_associations and changed nested_relationships to nested_associations_to_include

removed unneeded parameter from add_resource_relationships

simplify key check

added another test, showing multiple relationship serializers

refactored include_array_to_hash to a utils module - this also simplified the test for it. yay

lib/active_model/serializer/adapter/json.rb

@@ -7,37 +7,13 @@ class Json < Adapter
         def serializable_hash(options = nil)
           options ||= {}
           if serializer.respond_to?(:each)
-            @result = serializer.map { |s| FlattenJson.new(s).serializable_hash(options) }
+            @result = serialize_array_without_root(serializer, options)
           else
-            @hash = {}
+            @result = resource_object_for(serializer)
+            @result = add_resource_relationships(@result, serializer)
 
-            @core = cache_check(serializer) do
-              serializer.attributes(options)
-            end
 
-            serializer.associations.each do |association|
-              serializer = association.serializer
-              opts = association.options
-
-              if serializer.respond_to?(:each)
-                array_serializer = serializer
-                @hash[association.key] = array_serializer.map do |item|
-                  cache_check(item) do
-                    item.attributes(opts)
-                  end
-                end
-              else
-                @hash[association.key] =
-                  if serializer && serializer.object
-                    cache_check(serializer) do
-                      serializer.attributes(options)
-                    end
-                  elsif opts[:virtual_value]
-                    opts[:virtual_value]
-                  end
-              end
-            end
-            @result = @core.merge @hash
+            @result
           end
 
           { root => @result }
@@ -46,6 +22,111 @@ def serializable_hash(options = nil)
         def fragment_cache(cached_hash, non_cached_hash)
           Json::FragmentCache.new().fragment_cache(cached_hash, non_cached_hash)
         end
+
+        private
+
+        # iterate through the associations on the serializer,
+        # adding them to the parent as needed (as singular or plural)
+        #
+        # nested_associations is a list of symbols that governs what
+        # associations on the passed in seralizer to include
+        def add_resource_relationships(parent, serializer, nested_associations = [])
+          # have the include array normalized
+          nested_associations = ActiveModel::Serializer::Utils.include_array_to_hash(nested_associations)
+
+          included_associations = if nested_associations.present?
+            serializer.associations.select{ |association|
+              # nested_associations is a hash of:
+              #   key => nested association to include
+              nested_associations.has_key?(association.name)
+            }
+          else
+            serializer.associations
+          end
+
+          included_associations.each do |association|
+            serializer = association.serializer
+            opts = association.options
+            key = association.key
+
+            # sanity check if the association has nesting data
+            has_nesting = nested_associations[key].present?
+            if has_nesting
+              include_options_from_parent = { include: nested_associations[key] }
+              opts = opts.merge(include_options_from_parent)
+            end
+
+            if serializer.respond_to?(:each)
+              parent[key] = add_relationships(serializer, opts)
+            else
+              parent[key] = add_relationship(serializer, opts)
+            end
+          end
+
+          parent
+        end
+
+        # add a singular relationship
+        # the options should always belong to the serializer
+        def add_relationship(serializer, options)
+          serialized_relationship = serialized_or_virtual_of(serializer, options)
+
+          nested_associations_to_include = options[:include]
+          if nested_associations_to_include.present?
+            serialized_relationship = add_resource_relationships(
+              serialized_relationship,
+              serializer,
+              nested_associations_to_include)
+          end
+
+          serialized_relationship
+        end
+
+        # add a many relationship
+        def add_relationships(serializer, options)
+          serialize_array(serializer, options) do |serialized_item, item_serializer|
+            nested_associations_to_include = options[:include]
+
+            if nested_associations_to_include.present?
+              serialized_item = add_resource_relationships(
+                serialized_item,
+                item_serializer,
+                nested_associations_to_include)
+            end
+
+            serialized_item
+          end
+        end
+
+
+        def serialize_array_without_root(serializer, options)
+          serializer.map { |s| FlattenJson.new(s).serializable_hash(options) }
+        end
+
+        # a virtual value is something that doesn't need a serializer,
+        # such as a ruby array, or any other raw value
+        def serialized_or_virtual_of(serializer, options)
+          if serializer && serializer.object
+            resource_object_for(serializer)
+          elsif options[:virtual_value]
+            options[:virtual_value]
+          end
+        end
+
+        def serialize_array(serializer, options)
+          serializer.map do |item|
+            serialized_item = resource_object_for(item)
+            serialized_item = yield(serialized_item, item) if block_given?
+            serialized_item
+          end
+        end
+
+        def resource_object_for(serializer)
+          cache_check(serializer) do
+            serializer.attributes(serializer.options)
+          end
+        end
+
       end
     end
   end

lib/active_model/serializer/utils.rb

@@ -0,0 +1,42 @@
+module ActiveModel::Serializer::Utils
+  module_function
+
+    # converts the include hash to a standard format
+    # for constrained serialization recursion
+    #
+    # converts
+    #  [:author, :comments => [:author]] to
+    #  {:author => [], :comments => [:author]}
+    #
+    # and
+    #  [:author, :comments => {:author => :bio}, :posts => [:comments]] to
+    #  {:author => [], :comments => {:author => :bio}, :posts => [:comments]}
+    #
+    # The data passed in to this method should be an array where the last
+    # parameter is a hash
+    #
+    # the point of this method is to normalize the include
+    # options for the child relationships.
+    # if a sub inclusion is still an array after this method,
+    # it will get converted during the next iteration
+    def include_array_to_hash(include_array)
+      # still don't trust input
+      # but this also allows
+      #  include: :author syntax
+      include_array = Array[*include_array].compact
+
+      result = {}
+
+      hashes = include_array.select{|a| a.is_a?(Hash)}
+      non_hashes = include_array - hashes
+
+      hashes += non_hashes.map{ |association_name| { association_name => [] } }
+
+      # now merge all the hashes
+      hashes.each{|hash| result.merge!(hash) }
+
+      result
+    end
+
+
+end

lib/active_model_serializers.rb

@@ -14,6 +14,7 @@ def silence_warnings
 require 'action_controller'
 
 require 'active_model/serializer'
+require 'active_model/serializer/utils'
 require 'active_model/serializable_resource'
 require 'active_model/serializer/version'