1 files changed, 75 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index 3deb2d65f8..4aa323fb00 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -62,7 +62,15 @@ module ActiveRecord
   # Use that class method when you need to know the ordinal value of an enum:
   #
   #   Conversation.where("status <> ?", Conversation.statuses[:archived])
+  #
+  # Where conditions on an enum attribute must use the ordinal value of an enum.
   module Enum
+    DEFINED_ENUMS = {} # :nodoc:
+
+    def enum_mapping_for(attr_name) # :nodoc:
+      DEFINED_ENUMS[attr_name.to_s]
+    end
+
     def enum(definitions)
       klass = self
       definitions.each do |name, values|
@@ -71,10 +79,12 @@ module ActiveRecord
         name        = name.to_sym
 
         # def self.statuses statuses end
+        detect_enum_conflict!(name, name.to_s.pluralize, true)
         klass.singleton_class.send(:define_method, name.to_s.pluralize) { enum_values }
 
         _enum_methods_module.module_eval do
           # def status=(value) self[:status] = statuses[value] end
+          klass.send(:detect_enum_conflict!, name, "#{name}=")
           define_method("#{name}=") { |value|
             if enum_values.has_key?(value) || value.blank?
               self[name] = enum_values[value]
@@ -89,24 +99,31 @@ module ActiveRecord
           }
 
           # def status() statuses.key self[:status] end
+          klass.send(:detect_enum_conflict!, name, name)
           define_method(name) { enum_values.key self[name] }
 
           # def status_before_type_cast() statuses.key self[:status] end
+          klass.send(:detect_enum_conflict!, name, "#{name}_before_type_cast")
           define_method("#{name}_before_type_cast") { enum_values.key self[name] }
 
           pairs = values.respond_to?(:each_pair) ? values.each_pair : values.each_with_index
           pairs.each do |value, i|
             enum_values[value] = i
 
-            # scope :active, -> { where status: 0 }
-            klass.scope value, -> { klass.where name => i }
-
             # def active?() status == 0 end
+            klass.send(:detect_enum_conflict!, name, "#{value}?")
             define_method("#{value}?") { self[name] == i }
 
             # def active!() update! status: :active end
+            klass.send(:detect_enum_conflict!, name, "#{value}!")
             define_method("#{value}!") { update! name => value }
+
+            # scope :active, -> { where status: 0 }
+            klass.send(:detect_enum_conflict!, name, value, true)
+            klass.scope value, -> { klass.where name => i }
           end
+
+          DEFINED_ENUMS[name.to_s] = enum_values
         end
       end
     end
@@ -114,10 +131,64 @@ module ActiveRecord
     private
       def _enum_methods_module
         @_enum_methods_module ||= begin
-          mod = Module.new
+          mod = Module.new do
+            private
+              def save_changed_attribute(attr_name, value)
+                if (mapping = self.class.enum_mapping_for(attr_name))
+                  if attribute_changed?(attr_name)
+                    old = changed_attributes[attr_name]
+
+                    if mapping[old] == value
+                      changed_attributes.delete(attr_name)
+                    end
+                  else
+                    old = clone_attribute_value(:read_attribute, attr_name)
+
+                    if old != value
+                      changed_attributes[attr_name] = mapping.key old
+                    end
+                  end
+                else
+                  super
+                end
+              end
+          end
           include mod
           mod
         end
       end
+
+      ENUM_CONFLICT_MESSAGE = \
+        "You tried to define an enum named \"%{enum}\" on the model \"%{klass}\", but " \
+        "this will generate a %{type} method \"%{method}\", which is already defined " \
+        "by %{source}."
+
+      def detect_enum_conflict!(enum_name, method_name, klass_method = false)
+        if klass_method && dangerous_class_method?(method_name)
+          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
+            enum: enum_name,
+            klass: self.name,
+            type: 'class',
+            method: method_name,
+            source: 'Active Record'
+          }
+        elsif !klass_method && dangerous_attribute_method?(method_name)
+          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
+            enum: enum_name,
+            klass: self.name,
+            type: 'instance',
+            method: method_name,
+            source: 'Active Record'
+          }
+        elsif !klass_method && method_defined_within?(method_name, _enum_methods_module, Module)
+          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
+            enum: enum_name,
+            klass: self.name,
+            type: 'instance',
+            method: method_name,
+            source: 'another enum'
+          }
+        end
+      end
   end
 end