remove the hack in favor of a legit way

app/controllers/api/v2/mappings_controller.rb

@@ -6,19 +6,23 @@ module Api
         []
       end
 
+      def create
+        instantiate_resource
+        resource.user = current_user if current_user.present?
+        resource.updated_by = current_user if current_user.present?
+        authorize resource
+        create_action
+        respond_with_resource
+      end
+
       def update
-        # hack: set the user temporarily so the model hook can reference it, then set it back
-        temp = resource.user
-        resource.user = current_user
+        resource.updated_by = current_user if current_user.present?
         update_action
         respond_with_resource
-        resourse.user = temp
-        update_action
       end
 
       def destroy
-        # this is done so that the model hooks can use the mapping user to determine who took this action
-        resource.user = current_user if current_user.present? # current_user should always be present
+        resource.updated_by = current_user if current_user.present?
         destroy_action
         head :no_content
       end

app/controllers/mappings_controller.rb

@@ -19,6 +19,7 @@ class MappingsController < ApplicationController
     @mapping = Mapping.new(mapping_params)
     authorize @mapping
     @mapping.user = current_user
+    @mapping.updated_by = current_user
 
     if @mapping.save
       render json: @mapping, status: :created
@@ -31,9 +32,7 @@ class MappingsController < ApplicationController
   def update
     @mapping = Mapping.find(params[:id])
     authorize @mapping
-    # hack: set the user temporarily so that the model hook can reference it, and then set it back
-    temp = @mapping.user 
-    @mapping.user = current_user
+    @mapping.updated_by = current_user
     @mapping.assign_attributes(mapping_params)
 
     if @mapping.save
@@ -41,17 +40,13 @@ class MappingsController < ApplicationController
     else
       render json: @mapping.errors, status: :unprocessable_entity
     end
-    # restore the original mapping creator
-    @mapping.user = temp
-    @mapping.save
   end
 
   # DELETE /mappings/1.json
   def destroy
     @mapping = Mapping.find(params[:id])
     authorize @mapping
-    # hack: set the user temporarily so that the model hook can reference this user who is taking the action
-    @mapping.user = current_user
+    @mapping.updated_by = current_user
     @mapping.destroy
 
     head :no_content

app/models/mapping.rb

@@ -6,6 +6,7 @@ class Mapping < ApplicationRecord
   belongs_to :mappable, polymorphic: true
   belongs_to :map, class_name: 'Map', foreign_key: 'map_id', touch: true
   belongs_to :user
+  belongs_to :updated_by, class_name: 'User'
 
   validates :xloc, presence: true,
                    unless: proc { |m| m.mappable_type == 'Synapse' }
@@ -40,7 +41,7 @@ class Mapping < ApplicationRecord
   def after_updated
     if mappable_type == 'Topic' and (xloc_changed? or yloc_changed?)
       meta = {'x': xloc, 'y': yloc, 'mapping_id': id}
-      Events::TopicMovedOnMap.publish!(mappable, map, user, meta)
+      Events::TopicMovedOnMap.publish!(mappable, map, updated_by, meta)
     end
   end
 
@@ -53,9 +54,9 @@ class Mapping < ApplicationRecord
 
     meta = {'mapping_id': id}
     if mappable_type == 'Topic'
-      Events::TopicRemovedFromMap.publish!(mappable, map, user, meta)
+      Events::TopicRemovedFromMap.publish!(mappable, map, updated_by, meta)
     elsif mappable_type == 'Synapse'
-      Events::SynapseRemovedFromMap.publish!(mappable, map, user, meta)
+      Events::SynapseRemovedFromMap.publish!(mappable, map, updated_by, meta)
     end
   end
 end

app/serializers/api/v2/mapping_serializer.rb

@@ -14,6 +14,7 @@ module Api
       def self.embeddable
         {
           user: {},
+          updated_by: {},
           map: {}
         }
       end

db/migrate/20161216174257_add_updated_by_to_mappings.rb

@@ -0,0 +1,5 @@
+class AddUpdatedByToMappings < ActiveRecord::Migration[5.0]
+  def change
+      add_reference :mappings, :updated_by, foreign_key: {to_table: :users}
+  end
+end

doc/api/apis/mappings.raml

@@ -1,6 +1,6 @@
 #type: collection
 get:
-  is: [ embeddable: { embedFields: "user,map" }, orderable, pageable ]
+  is: [ embeddable: { embedFields: "user,updated_by,map" }, orderable, pageable ]
   securedBy: [ null, token, oauth_2_0, cookie ]
   responses:
     200:
@@ -31,7 +31,7 @@ post:
 /{id}:
   #type: item
   get:
-    is: [ embeddable: { embedFields: "user,map" } ]
+    is: [ embeddable: { embedFields: "user,updated_by,map" } ]
     securedBy: [ null, token, oauth_2_0, cookie ]
     responses:
       200:

doc/api/examples/mapping.json

@@ -6,6 +6,7 @@
     "mappable_id": 1,
     "mappable_type": "Synapse",
     "user_id": 1,
+    "updated_by_id": 1,
     "map_id": 1
   }
 }

doc/api/examples/mappings.json

@@ -8,6 +8,7 @@
       "mappable_type": "Topic",
       "updated_at": "2016-03-25T08:44:07.152Z",
       "user_id": 1,
+      "updated_by_id": 1,
       "xloc": -271,
       "yloc": 22
     },
@@ -19,6 +20,7 @@
       "mappable_type": "Topic",
       "updated_at": "2016-03-25T08:44:13.907Z",
       "user_id": 1,
+      "updated_by_id": 1,
       "xloc": -12,
       "yloc": 61
     },
@@ -30,6 +32,7 @@
       "mappable_type": "Topic",
       "updated_at": "2016-03-25T08:44:19.333Z",
       "user_id": 1,
+      "updated_by_id": 1,
       "xloc": -93,
       "yloc": -90
     },
@@ -40,7 +43,8 @@
       "mappable_id": 1,
       "mappable_type": "Synapse",
       "updated_at": "2016-03-25T08:44:21.337Z",
-      "user_id": 1
+      "user_id": 1,
+      "updated_by_id": 1
     }
   ],
   "page": {

doc/api/schemas/_mapping.json

@@ -35,6 +35,12 @@
     },
     "user": {
       "$ref": "_user.json"
+    },
+    "updated_by_id": {
+      "$ref": "_id.json"
+    },
+    "updated_by": {
+      "$ref": "_user.json"
     }
   },
   "required": [
@@ -56,6 +62,12 @@
         { "required": [ "user_id" ] },
         { "required": [ "user" ] }
       ]
+    },
+    {
+      "oneOf": [
+        { "required": [ "updated_by_id" ] },
+        { "required": [ "updated_by" ] }
+      ]
     }
   ]
 }