kirel · April 25, 2017 09:54 · Nov 22, 2013 · Nov 22, 2013
diff --git a/build_sti_subclass.rb b/build_sti_subclass.rb
@@ -1,6 +1,5 @@
-# STI subclass building backported from
+# STI subclass building backported from Rails 4 to use in Rails 3.2 - see
 # https://github.com/rails/rails/commit/89b5b31cc4f8407f648a2447665ef23f9024e8a5
-# use on demand by extending classes you want this for by including this module
 # Usage:
 #   include BuildStiSubclass # in your model and be done
 module BuildStiSubclass

diff --git a/build_sti_subclass.rb b/build_sti_subclass.rb
@@ -0,0 +1,38 @@
+# STI subclass building backported from
+# https://github.com/rails/rails/commit/89b5b31cc4f8407f648a2447665ef23f9024e8a5
+# use on demand by extending classes you want this for by including this module
+# Usage:
+#   include BuildStiSubclass # in your model and be done
+module BuildStiSubclass
+  extend ActiveSupport::Concern
+  included do
+    attr_accessible inheritance_column
+  end
+  module ClassMethods
+    # Determines if one of the attributes passed in is the inheritance column,
+    # and if the inheritance column is attr accessible, it initializes an
+    # instance of the given subclass instead of the base class
+    def new(*args, &block)
+      if (attrs = args.first).is_a?(Hash)
+        if subclass = subclass_from_attrs(attrs)
+          return subclass.new(*args, &block)
+        end
+      end
+      # Delegate to the original .new
+      super
+    end
+
+    # Detect the subclass from the inheritance column of attrs. If the inheritance column value
+    # is not self or a valid subclass, raises ActiveRecord::SubclassNotFound
+    # If this is a StrongParameters hash, and access to inheritance_column is not permitted,
+    # this will ignore the inheritance column and return nil
+    def subclass_from_attrs(attrs)
+      subclass_name = attrs.with_indifferent_access[inheritance_column]
+      return nil if subclass_name.blank? || subclass_name == self.name
+      unless subclass = subclasses.detect { |sub| sub.name == subclass_name }
+        raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass_name} is not a subclass of #{name}")
+      end
+      subclass
+    end
+  end
+end