9 files changed, 34 insertions, 13 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index c3ded8d4a9..4b39791b73 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Fix subtle bugs regarding attribute assignment on models with no primary
+    key. `'id'` will no longer be part of the attributes hash.
+
+    *Sean Griffin*
+
 *   Deprecate automatic counter caches on `has_many :through`. The behavior was
     broken and inconsistent.
 
diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
index 33c20bb5cc..6d38224830 100644
--- a/activerecord/lib/active_record/attribute.rb
+++ b/activerecord/lib/active_record/attribute.rb
@@ -90,6 +90,11 @@ module ActiveRecord
       def value
         nil
       end
+
+      def with_value_from_database(value)
+        raise ActiveModel::MissingAttributeError, "can't write unknown attribute `#{name}`"
+      end
+      alias_method :with_value_from_user, :with_value_from_database
     end
 
     class Uninitialized < Attribute # :nodoc:
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index 1c81a5b71b..cadad60ddd 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -83,12 +83,9 @@ module ActiveRecord
         end
 
         def get_primary_key(base_name) #:nodoc:
-          return 'id' if base_name.blank?
-
-          case primary_key_prefix_type
-          when :table_name
+          if base_name && primary_key_prefix_type == :table_name
             base_name.foreign_key(false)
-          when :table_name_with_underscore
+          elsif base_name && primary_key_prefix_type == :table_name_with_underscore
             base_name.foreign_key
           else
             if ActiveRecord::Base != self && table_exists?
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index 94fce2db60..b3c8209a74 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -70,10 +70,6 @@ module ActiveRecord
         attr_name = attr_name.to_s
         attr_name = self.class.primary_key if attr_name == 'id' && self.class.primary_key
 
-        unless has_attribute?(attr_name) || self.class.columns_hash.key?(attr_name)
-          raise ActiveModel::MissingAttributeError, "can't write unknown attribute `#{attr_name}'"
-        end
-
         if should_type_cast
           @attributes.write_from_user(attr_name, value)
         else
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 3ef8878ad1..def04dbed2 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -381,7 +381,7 @@ module ActiveRecord
       end
 
       def table_exists?(name)
-        return false unless name
+        return false unless name.present?
         return true if tables(nil, nil, name).any?
 
         name          = name.to_s
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index c434b0d40a..3321e268d5 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -521,7 +521,7 @@ module ActiveRecord
 
     def init_internals
       pk = self.class.primary_key
-      unless @attributes.include?(pk)
+      if pk && !@attributes.include?(pk)
         @attributes.write_from_database(pk, nil)
       end
 
diff --git a/activerecord/test/cases/attribute_methods_test.rb b/activerecord/test/cases/attribute_methods_test.rb
index 7566af920f..2048e0d5ad 100644
--- a/activerecord/test/cases/attribute_methods_test.rb
+++ b/activerecord/test/cases/attribute_methods_test.rb
@@ -253,6 +253,15 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal @loaded_fixtures['computers']['workstation'].to_hash, Computer.first.attributes
   end
 
+  def test_attributes_without_primary_key
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = 'developers_projects'
+    end
+
+    assert_equal klass.column_names, klass.new.attributes.keys
+    assert_not klass.new.attributes.key?('id')
+  end
+
   def test_hashes_not_mangled
     new_topic = { :title => "New Topic" }
     new_topic_values = { :title => "AnotherTopic" }
diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index f43483d291..b04df7ce43 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -134,14 +134,22 @@ class PrimaryKeysTest < ActiveRecord::TestCase
   end
 
   def test_primary_key_returns_value_if_it_exists
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = 'developers'
+    end
+
     if ActiveRecord::Base.connection.supports_primary_key?
-      assert_equal 'id', ActiveRecord::Base.connection.primary_key('developers')
+      assert_equal 'id', klass.primary_key
     end
   end
 
   def test_primary_key_returns_nil_if_it_does_not_exist
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = 'developers_projects'
+    end
+
     if ActiveRecord::Base.connection.supports_primary_key?
-      assert_nil ActiveRecord::Base.connection.primary_key('developers_projects')
+      assert_nil klass.primary_key
     end
   end
 
diff --git a/activerecord/test/models/contact.rb b/activerecord/test/models/contact.rb
index a1cb8d62b6..3ea17c3abf 100644
--- a/activerecord/test/models/contact.rb
+++ b/activerecord/test/models/contact.rb
@@ -8,6 +8,7 @@ module ContactFakeColumns
         table_name => 'id'
       }
 
+      column :id,             :integer
       column :name,           :string
       column :age,            :integer
       column :avatar,         :binary