Always add _attributes params for empty or nil relationships

lib/jsonapi_parameters/default_handlers/empty_to_many_relation_handler.rb

@@ -0,0 +1,22 @@
+require 'active_support/inflector'
+
+module JsonApi
+  module Parameters
+    module Handlers
+      module DefaultHandlers
+        class EmptyToManyRelationHandler < BaseHandler
+          include ActiveSupport::Inflector
+
+          attr_reader :with_inclusion, :vals, :key
+
+          def handle
+            [
+              ["#{pluralize(relationship_key)}_attributes".to_sym, []],
+              ["#{singularize(relationship_key)}_ids".to_sym, []]
+            ]
+          end
+        end
+      end
+    end
+  end
+end

lib/jsonapi_parameters/default_handlers/empty_to_one_relation_handler.rb

@@ -0,0 +1,22 @@
+require 'active_support/inflector'
+
+module JsonApi
+  module Parameters
+    module Handlers
+      module DefaultHandlers
+        class EmptyToOneRelationHandler < BaseHandler
+          include ActiveSupport::Inflector
+
+          attr_reader :with_inclusion, :vals, :key
+
+          def handle
+            [
+              ["#{singularize(relationship_key)}_attributes".to_sym, {}],
+              ["#{singularize(relationship_key)}_id".to_sym, nil]
+            ]
+          end
+        end
+      end
+    end
+  end
+end

lib/jsonapi_parameters/default_handlers/nil_relation_handler.rb

@@ -20,7 +20,7 @@ def handle
             end
 
             # Handle with empty hash.
-            ToOneRelationHandler.new(relationship_key, {}, {}).handle
+            EmptyToOneRelationHandler.new(relationship_key, {}, {}).handle
           end
         end
       end

lib/jsonapi_parameters/handlers.rb

@@ -1,13 +1,16 @@
 require_relative 'default_handlers/nil_relation_handler'
 require_relative 'default_handlers/to_many_relation_handler'
 require_relative 'default_handlers/to_one_relation_handler'
+require_relative 'default_handlers/empty_to_one_relation_handler'
+require_relative 'default_handlers/empty_to_many_relation_handler'
 
 module JsonApi
   module Parameters
     module Handlers
       include DefaultHandlers
 
       DEFAULT_HANDLER_SET = {
+        empty_to_many: EmptyToManyRelationHandler,
         to_many: ToManyRelationHandler,
         to_one: ToOneRelationHandler,
         nil: NilRelationHandler

lib/jsonapi_parameters/translator.rb

@@ -72,6 +72,8 @@ def handle_relationships(param, relationship_key, relationship_value)
                 Handlers.handlers[Handlers.resource_handlers[relationship_key]]
               else
                 case relationship_value
+                when []
+                  Handlers.handlers[:empty_to_many]
                 when Array
                   Handlers.handlers[:to_many]
                 when Hash
@@ -83,15 +85,26 @@ def handle_relationships(param, relationship_key, relationship_value)
                 end
               end
 
-    key, val = handler.call(*handler_args)
+    handled_params = handler.call(*handler_args)
 
-    param[key] = handle_nested_relationships(val)
+    add_relationships_to_params(handled_params, param)
 
     param
   ensure
     decrement_stack_level
   end
 
+  def add_relationships_to_params(handled_params, param)
+    if handled_params.all?(Array)
+      handled_params.each do |key, val|
+        param[key] = handle_nested_relationships(val)
+      end
+    else
+      key, val = *handled_params
+      param[key] = handle_nested_relationships(val)
+    end
+  end
+
   def handle_nested_relationships(val)
     # We can only consider Hash relationships (which imply to-one relationship) and Array relationships (which imply to-many).
     # Each type has a different handling method, though in both cases we end up passing the nested relationship recursively to handle_relationship

spec/support/inputs_outputs_pairs.rb

@@ -482,7 +482,8 @@ module JsonApi::Parameters::Testing
           photo: {
             title: 'Ember Hamster',
             src: 'http://example.com/images/productivity.png',
-            photographer_ids: []
+            photographer_ids: [],
+            photographers_attributes: []
           }
         }
       ] },
@@ -505,7 +506,8 @@ module JsonApi::Parameters::Testing
           account: {
             name: 'Bob Loblaw',
             profile_url: 'http://example.com/images/no-nonsense.png',
-            owner_id: nil
+            owner_id: nil,
+            owner_attributes: []
           }
         }
       ] },
@@ -526,7 +528,7 @@ module JsonApi::Parameters::Testing
         },
         {
           user: {
-            name: 'Adam Joe', practice_area_ids: [],
+            name: 'Adam Joe', practice_area_ids: [], practice_areas_attributes: []
           }
         }
       ] },
@@ -546,7 +548,7 @@ module JsonApi::Parameters::Testing
         },
         {
           user: {
-            name: 'Adam Joe', practice_area_ids: [],
+            name: 'Adam Joe', practice_area_ids: [], practice_areas_attributes: []
           }
         }
       ] },