Support for create_association! for has_one associations

activerecord/lib/active_record/associations.rb

@@ -1536,6 +1536,7 @@ module ActiveRecord
             "build_#{reflection.name}"  => "build",
             "create_#{reflection.name}" => "create"
           }
+          constructors["create_#{reflection.name}!"] = "create!" if reflection.macro == :has_one
 
           constructors.each do |name, proxy_name|
             redefine_method(name) do |*params|

activerecord/lib/active_record/associations/has_one_association.rb

@@ -7,7 +7,7 @@ module ActiveRecord
       end
 
       def create!(attributes = {})
-        new_record(:create_association!, attributes)
+        build(attributes).tap { |record| record.save! }
       end
 
       def build(attributes = {})
@@ -51,6 +51,9 @@ module ActiveRecord
 
         alias creation_attributes construct_owner_attributes
 
+        # The reason that the save param for replace is false, if for create (not just build),
+        # is because the setting of the foreign keys is actually handled by the scoping, and
+        # so they are set straight away and do not need to be updated within replace.
         def new_record(method, attributes)
           record = scoped.scoping { @reflection.send(method, attributes) }
           replace(record, false)

activerecord/test/cases/associations/has_one_associations_test.rb

@@ -173,6 +173,24 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     assert_equal account, firm.reload.account
   end
 
+  def test_create_association_with_bang
+    firm = Firm.create(:name => "GlobalMegaCorp")
+    account = firm.create_account!(:credit_limit => 1000)
+    assert_equal account, firm.reload.account
+  end
+
+  def test_create_association_with_bang_failing
+    firm = Firm.create(:name => "GlobalMegaCorp")
+    assert_raise ActiveRecord::RecordInvalid do
+      firm.create_account!
+    end
+    account = firm.account
+    assert_not_nil account
+    account.credit_limit = 5
+    account.save
+    assert_equal account, firm.reload.account
+  end
+
   def test_build
     firm = Firm.new("name" => "GlobalMegaCorp")
     firm.save