Extract condition as define_autosave_method?

lib/mongoid/attributes/nested.rb

@@ -83,19 +83,32 @@ def autosave_nested_attributes(association)
           # marked as autosave despite the fact that the option isn't present. Because the method
           # Association#autosave? is implemented by checking the autosave option, this is the most
           # straightforward way to mark it.
-          #
-          # If autosave option for association is present but is set as false, then association will
-          # be checked if it is one of the values of `nested_attributes`. If existing, then association
-          # will be marked as autosave.
-          is_nested = is_association_nested_attribute?(association)
-          if association.autosave? || ((association.options[:autosave].nil? || is_nested) && !association.embedded?)
+          if define_autosave_method?(association)
             association.options[:autosave] = true
             Association::Referenced::AutoSave.define_autosave!(association)
           end
         end
 
-        def is_association_nested_attribute?(association)
-          !!nested_attributes[association.name.to_s + '_attributes']
+        # Check if autosave method can be defined for the nested association.
+        #
+        # @api private
+        #
+        # @example Check if to define autosave method.
+        #   Person.define_autosave_method?(metadata)
+        #
+        # @param [ Mongoid::Association::Relatable ] association The existing association metadata.
+        def define_autosave_method?(association)
+          # autosave method can be defined in one of these cases:
+          #
+          # 1. autosave is explicitly set in association
+          return true if association.autosave?
+
+          is_nested = !!nested_attributes[association.name.to_s + '_attributes']
+
+          # 2. association is referenced (non-embedded), and
+          #    a. autosave is not set in association, or
+          #    b. association is defined as nested attributes via `accepts_nested_attributes_for`
+          (association.options[:autosave].nil? || is_nested) && !association.embedded?
         end
       end
     end