Utilise ActiveModel::Serializers::JSON in Her models

This makes as_json and to_json behave like they do under ActiveRecord,
excluding associations unless they are explicitly included. This is
necessary to avoid infinite loops.

Unfortunately this caused Her's include_root_in_json code to collide
with ActiveModel's include_root_in_json code. I removed Her's
getter/setter method in favour of ActiveModel's class attribute but
also provided a compatibility fix.

lib/her/model.rb

@@ -1,3 +1,4 @@
+require "active_model"
 require "her/model/base"
 require "her/model/deprecated_methods"
 require "her/model/http"
@@ -7,9 +8,9 @@
 require "her/model/parse"
 require "her/model/associations"
 require "her/model/introspection"
+require "her/model/serialization"
 require "her/model/paths"
 require "her/model/nested_attributes"
-require "active_model"
 
 module Her
   # This module is the main element of Her. After creating a Her::API object,
@@ -33,6 +34,7 @@ module Model
     include Her::Model::HTTP
     include Her::Model::Parse
     include Her::Model::Introspection
+    include Her::Model::Serialization
     include Her::Model::Paths
     include Her::Model::Associations
     include Her::Model::NestedAttributes

lib/her/model/parse.rb

@@ -51,7 +51,7 @@ def to_params(attributes, changes={})
 
           embed_params!(attributes, filtered_attributes)
 
-          if include_root_in_json?
+          if include_root_in_json
             if json_api_format?
               { included_root_element => [filtered_attributes] }
             else
@@ -101,18 +101,6 @@ def embed_params!(read_attributes, write_attributes)
           Thread.current[:her_embedded_params_objects] = nil if first
         end
 
-        # Return or change the value of `include_root_in_json`
-        #
-        # @example
-        #   class User
-        #     include Her::Model
-        #     include_root_in_json true
-        #   end
-        def include_root_in_json(value, options = {})
-          @_her_include_root_in_json = value
-          @_her_include_root_in_json_format = options[:format]
-        end
-
         # Return or change the value of `parse_root_in_json`
         #
         # @example
@@ -176,7 +164,7 @@ def root_element_included?(data)
 
         # @private
         def included_root_element
-          include_root_in_json? == true ? root_element : include_root_in_json?
+          include_root_in_json == true ? root_element : include_root_in_json
         end
 
         # Extract an array from the request data
@@ -234,12 +222,6 @@ def request_new_object_on_build?
           superclass.respond_to?(:request_new_object_on_build?) && superclass.request_new_object_on_build?
         end
 
-        # @private
-        def include_root_in_json?
-          return @_her_include_root_in_json unless @_her_include_root_in_json.nil?
-          superclass.respond_to?(:include_root_in_json?) && superclass.include_root_in_json?
-        end
-
         # @private
         def parse_root_in_json?
           return @_her_parse_root_in_json unless @_her_parse_root_in_json.nil?

lib/her/model/serialization.rb

@@ -0,0 +1,49 @@
+module Her
+  module Model
+    module Serialization
+      extend ActiveSupport::Concern
+      include ActiveModel::Serializers::JSON
+
+      def serializable_hash(options = nil)
+        options = options.try(:dup) || {}
+
+        options[:except] = Array(options[:except]).map(&:to_s)
+        options[:except] |= self.class.association_names.map(&:to_s)
+
+        super(options)
+      end
+
+      included do
+        # Rails 3 defaulted to true but Her has always defaulted to
+        # false. This can be dropped when Rails 3 support is dropped.
+        self.include_root_in_json = false
+
+        # Rails creates include_root_in_json as a class attribute but
+        # Her previously had its own implementation combining the
+        # getter and setter. This monstrosity tries to achieve
+        # compatibility in the simplest way possible.
+        class << self
+          realias = proc do
+            alias_method :include_root_in_json_getter, :include_root_in_json
+
+            def include_root_in_json(value = nil)
+              if value.nil?
+                include_root_in_json_getter
+              else
+                self.include_root_in_json = value
+              end
+            end
+          end
+
+          realias.call
+          alias_method :include_root_in_json_without_realias, :include_root_in_json=
+
+          define_method :include_root_in_json= do |value|
+            include_root_in_json_without_realias value
+            realias.call
+          end
+        end
+      end
+    end
+  end
+end