1 files changed, 61 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations/singular_association.rb b/activerecord/lib/active_record/associations/singular_association.rb
new file mode 100644
index 0000000000..c296f9882e
--- /dev/null
+++ b/activerecord/lib/active_record/associations/singular_association.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module Associations
+    class SingularAssociation < Association #:nodoc:
+      # Implements the reader method, e.g. foo.bar for Foo.has_one :bar
+      def reader
+        if !loaded? || stale_target?
+          reload
+        end
+
+        target
+      end
+
+      # Implements the writer method, e.g. foo.bar= for Foo.belongs_to :bar
+      def writer(record)
+        replace(record)
+      end
+
+      def build(attributes = {}, &block)
+        record = build_record(attributes, &block)
+        set_new_record(record)
+        record
+      end
+
+      # Implements the reload reader method, e.g. foo.reload_bar for
+      # Foo.has_one :bar
+      def force_reload_reader
+        reload(true)
+        target
+      end
+
+      private
+        def scope_for_create
+          super.except!(klass.primary_key)
+        end
+
+        def find_target
+          super.first
+        rescue ::RangeError
+          nil
+        end
+
+        def replace(record)
+          raise NotImplementedError, "Subclasses must implement a replace(record) method"
+        end
+
+        def set_new_record(record)
+          replace(record)
+        end
+
+        def _create_record(attributes, raise_error = false, &block)
+          record = build_record(attributes, &block)
+          saved = record.save
+          set_new_record(record)
+          raise RecordInvalid.new(record) if !saved && raise_error
+          record
+        end
+    end
+  end
+end