Add support for has_one :x, polymorphic: true

README.md

@@ -239,31 +239,34 @@ end
 ##### Options
 
 The association methods support the following options:
+
  * `class_name` - a string specifying the underlying class for the related resource
- * `foreign_key` - the method on the resource used to fetch the related resource. Defaults to `<resource_name>_id` for 
-    has_one and `<resource_name>_ids` for has_many relationships.
+ * `foreign_key` - the method on the resource used to fetch the related resource. Defaults to `<resource_name>_id` for has_one and `<resource_name>_ids` for has_many relationships.
  * `acts_as_set` - allows the entire set of related records to be replaced in one operation. Defaults to false if not set.
- * `relation_name` - the name of the relation to use on the model. A lambda may be provided which allows conditional 
-    selection of the relation based on the context.
-    
+ * `relation_name` - the name of the relation to use on the model. A lambda may be provided which allows conditional selection of the relation based on the context.
+ * `polymorphic` - set to true to identify `has_one` associations that are polymorphic.
+
 Examples:
 
 ```ruby
- class CommentResource < JSONAPI::Resource
+class CommentResource < JSONAPI::Resource
   attributes :body
   has_one :post
   has_one :author, class_name: 'Person'
   has_many :tags, acts_as_set: true
- end
-```
+end
 
-```ruby
 class ExpenseEntryResource < JSONAPI::Resource
   attributes :cost, :transaction_date
 
   has_one :currency, class_name: 'Currency', foreign_key: 'currency_code'
   has_one :employee
 end
+
+class TagResource < JSONAPI::Resource
+  attributes :name
+  has_one :taggable, polymorphic: true
+end
 ```
 
 ```ruby
@@ -283,8 +286,14 @@ class BookResource < JSONAPI::Resource
   }
   ...
 end
-```
 
+The polymorphic association will require the resource and controller to exist, although routing to them will cause an error.
+
+```ruby
+class TaggableResource < JSONAPI::Resource; end
+class TaggablesController < JSONAPI::ResourceController; end
+```
+
 #### Filters
 
 Filters for locating objects of the resource type are specified in the resource definition. Single filters can be 

lib/jsonapi/association.rb

@@ -1,16 +1,20 @@
 module JSONAPI
   class Association
-    attr_reader :acts_as_set, :foreign_key, :type, :options, :name, :class_name
+    attr_reader :acts_as_set, :foreign_key, :type, :options, :name,
+                :class_name, :polymorphic
 
     def initialize(name, options = {})
-      @name                = name.to_s
-      @options             = options
-      @acts_as_set         = options.fetch(:acts_as_set, false) == true
-      @foreign_key         = options[:foreign_key] ? options[:foreign_key].to_sym : nil
-      @module_path         = options[:module_path] || ''
-      @relation_name       = options.fetch(:relation_name, @name)
+      @name = name.to_s
+      @options = options
+      @acts_as_set = options.fetch(:acts_as_set, false) == true
+      @foreign_key = options[:foreign_key] ? options[:foreign_key].to_sym : nil
+      @module_path = options[:module_path] || ''
+      @relation_name = options.fetch(:relation_name, @name)
+      @polymorphic = options.fetch(:polymorphic, false) == true
     end
 
+    alias_method :polymorphic?, :polymorphic
+
     def primary_key
       @primary_key ||= resource_klass._primary_key
     end
@@ -32,13 +36,26 @@ def relation_name(options = {})
       end
     end
 
+    def type_for_source(source)
+      if polymorphic?
+        resource = source.public_send(name)
+        resource.class._type if resource
+      else
+        type
+      end
+    end
+
     class HasOne < Association
       def initialize(name, options = {})
         super
         @class_name = options.fetch(:class_name, name.to_s.camelize)
         @type = class_name.underscore.pluralize.to_sym
         @foreign_key ||= "#{name}_id".to_sym
       end
+
+      def polymorphic_type
+        "#{type.to_s.singularize}_type" if polymorphic?
+      end
     end
 
     class HasMany < Association

lib/jsonapi/operation.rb

@@ -236,6 +236,25 @@ def apply
     end
   end
 
+  class ReplacePolymorphicHasOneAssociationOperation < Operation
+    attr_reader :resource_id, :association_type, :key_value, :key_type
+
+    def initialize(resource_klass, options = {})
+      @resource_id = options.fetch(:resource_id)
+      @key_value = options.fetch(:key_value)
+      @key_type = options.fetch(:key_type)
+      @association_type = options.fetch(:association_type).to_sym
+      super(resource_klass, options)
+    end
+
+    def apply
+      resource = @resource_klass.find_by_key(@resource_id, context: @context)
+      result = resource.replace_polymorphic_has_one_link(@association_type, @key_value, @key_type)
+
+      return JSONAPI::OperationResult.new(result == :completed ? :no_content : :accepted)
+    end
+  end
+
   class CreateHasManyAssociationOperation < Operation
     attr_reader :resource_id, :association_type, :data
 

lib/jsonapi/operations_processor.rb

@@ -12,6 +12,7 @@ class OperationsProcessor
                                        :remove_resource_operation,
                                        :replace_fields_operation,
                                        :replace_has_one_association_operation,
+                                       :replace_polymorphic_has_one_association_operation,
                                        :create_has_many_association_operation,
                                        :replace_has_many_association_operation,
                                        :remove_has_many_association_operation,

lib/jsonapi/request.rb

@@ -185,7 +185,7 @@ def check_include(resource_klass, include_parts)
       association = resource_klass._association(association_name)
       if association && format_key(association_name) == include_parts.first
         unless include_parts.last.empty?
-          check_include(Resource.resource_for(@resource_klass.module_path + association.class_name.to_s), include_parts.last.partition('.'))
+          check_include(Resource.resource_for(@resource_klass.module_path + association.class_name.to_s.underscore), include_parts.last.partition('.'))
         end
       else
         @errors.concat(JSONAPI::Exceptions::InvalidInclude.new(format_key(resource_klass._type),
@@ -403,11 +403,8 @@ def parse_params(params, allowed_fields)
               end
 
               links_object = parse_has_one_links_object(linkage)
-              # Since we do not yet support polymorphic associations we will raise an error if the type does not match the
-              # association's type.
-              # TODO: Support Polymorphic associations
-              if links_object[:type] && (links_object[:type].to_s != association.type.to_s)
-                fail JSONAPI::Exceptions::TypeMismatch.new(links_object[:type])
+              if !association.polymorphic? && links_object[:type] && (links_object[:type].to_s != association.type.to_s)
+                raise JSONAPI::Exceptions::TypeMismatch.new(links_object[:type])
               end
 
               unless links_object[:id].nil?
@@ -520,18 +517,31 @@ def parse_add_association_operation(data, association_type, parent_key)
 
     def parse_update_association_operation(data, association_type, parent_key)
       association = resource_klass._association(association_type)
-
       if association.is_a?(JSONAPI::Association::HasOne)
-        object_params = { relationships: { format_key(association.name) => { data: data } } }
-        verified_param_set = parse_params(object_params, updatable_fields)
-
-        @operations.push JSONAPI::ReplaceHasOneAssociationOperation.new(
-          resource_klass,
-          context: @context,
-          resource_id: parent_key,
-          association_type: association_type,
-          key_value: verified_param_set[:has_one].values[0]
-        )
+        if association.polymorphic?
+          object_params = {relationships: {format_key(association.name) => {data: data}}}
+          verified_param_set = parse_params(object_params, updatable_fields)
+
+          @operations.push JSONAPI::ReplacePolymorphicHasOneAssociationOperation.new(
+                             resource_klass,
+                             context: @context,
+                             resource_id: parent_key,
+                             association_type: association_type,
+                             key_value: verified_param_set[:has_one].values[0],
+                             key_type: data['type']
+                           )
+        else
+          object_params = {relationships: {format_key(association.name) => {data: data}}}
+          verified_param_set = parse_params(object_params, updatable_fields)
+
+          @operations.push JSONAPI::ReplaceHasOneAssociationOperation.new(
+                             resource_klass,
+                             context: @context,
+                             resource_id: parent_key,
+                             association_type: association_type,
+                             key_value: verified_param_set[:has_one].values[0]
+                           )
+        end
       else
         unless association.acts_as_set
           fail JSONAPI::Exceptions::HasManySetReplacementForbidden.new
@@ -541,12 +551,12 @@ def parse_update_association_operation(data, association_type, parent_key)
         verified_param_set = parse_params(object_params, updatable_fields)
 
         @operations.push JSONAPI::ReplaceHasManyAssociationOperation.new(
-          resource_klass,
-          context: @context,
-          resource_id: parent_key,
-          association_type: association_type,
-          data: verified_param_set[:has_many].values[0]
-        )
+                           resource_klass,
+                           context: @context,
+                           resource_id: parent_key,
+                           association_type: association_type,
+                           data: verified_param_set[:has_many].values[0]
+                         )
       end
     end
 

lib/jsonapi/resource.rb

@@ -17,6 +17,7 @@ class Resource
                                        :replace_has_many_links,
                                        :create_has_one_link,
                                        :replace_has_one_link,
+                                       :replace_polymorphic_has_one_link,
                                        :remove_has_many_link,
                                        :remove_has_one_link,
                                        :replace_fields
@@ -79,6 +80,12 @@ def replace_has_one_link(association_type, association_key_value)
       end
     end
 
+    def replace_polymorphic_has_one_link(association_type, association_key_value, association_key_type)
+      change :replace_polymorphic_has_one_link do
+        _replace_polymorphic_has_one_link(association_type, association_key_value, association_key_type)
+      end
+    end
+
     def remove_has_many_link(association_type, key)
       change :remove_has_many_link do
         _remove_has_many_link(association_type, key)
@@ -188,6 +195,17 @@ def _replace_has_one_link(association_type, association_key_value)
       :completed
     end
 
+    def _replace_polymorphic_has_one_link(association_type, key_value, key_type)
+      association = self.class._associations[association_type]
+
+      send("#{association.foreign_key}=", key_value)
+      send("#{association.polymorphic_type}=", key_type.singularize.capitalize)
+
+      @save_needed = true
+
+      :completed
+    end
+
     def _remove_has_many_link(association_type, key)
       association = self.class._associations[association_type]
 
@@ -632,12 +650,11 @@ def _associate(klass, *attrs)
 
         attrs.each do |attr|
           check_reserved_association_name(attr)
-
-          association = @_associations[attr] = klass.new(attr, options)
+          @_associations[attr] = association = klass.new(attr, options)
 
           associated_records_method_name = case association
-                                             when JSONAPI::Association::HasOne then "record_for_#{attr}"
-                                             when JSONAPI::Association::HasMany then "records_for_#{attr}"
+                                           when JSONAPI::Association::HasOne then "record_for_#{attr}"
+                                           when JSONAPI::Association::HasMany then "records_for_#{attr}"
                                            end
 
           foreign_key = association.foreign_key
@@ -657,10 +674,16 @@ def _associate(klass, *attrs)
             end unless method_defined?(foreign_key)
 
             define_method attr do |options = {}|
-              resource_klass = association.resource_klass
-              if resource_klass
+              if association.polymorphic?
                 associated_model = public_send(associated_records_method_name)
-                return associated_model ? resource_klass.new(associated_model, @context) : nil
+                resource_klass = Resource.resource_for(self.class.module_path + associated_model.class.to_s.underscore) if associated_model
+                return resource_klass.new(associated_model, @context) if resource_klass
+              else
+                resource_klass = association.resource_klass
+                if resource_klass
+                  associated_model = public_send(associated_records_method_name)
+                  return associated_model ? resource_klass.new(associated_model, @context) : nil
+                end
               end
             end unless method_defined?(attr)
           elsif association.is_a?(JSONAPI::Association::HasMany)

lib/jsonapi/resource_serializer.rb

@@ -168,6 +168,7 @@ def relationship_data(source, include_directives)
               resource = source.send(name)
               if resource
                 id = resource.id
+                type = association.type_for_source(source)
                 associations_only = already_serialized?(type, id)
                 if include_linkage && !associations_only
                   add_included_object(type, id, object_hash(resource, ia))
@@ -232,7 +233,7 @@ def has_one_linkage(source, association)
       linkage = {}
       linkage_id = foreign_key_value(source, association)
       if linkage_id
-        linkage[:type] = format_key(association.type)
+        linkage[:type] = format_key(association.type_for_source(source))
         linkage[:id] = linkage_id
       else
         linkage = nil

lib/jsonapi/routing_ext.rb

@@ -163,8 +163,13 @@ def jsonapi_related_resource(*association)
           association = source._associations[association_name]
 
           formatted_association_name = format_route(association.name)
-          related_resource = JSONAPI::Resource.resource_for(resource_type_with_module_prefix(association.class_name.underscore.pluralize))
-          options[:controller] ||= related_resource._type.to_s
+
+          if association.polymorphic?
+            options[:controller] ||= association.class_name.underscore.pluralize
+          else
+            related_resource = JSONAPI::Resource.resource_for(resource_type_with_module_prefix(association.class_name.underscore.pluralize))
+            options[:controller] ||= related_resource._type.to_s
+          end
 
           match "#{formatted_association_name}", controller: options[:controller],
                                                  association: association.name, source: resource_type_with_module_prefix(source._type),