1 files changed, 12 insertions, 8 deletions
diff --git a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
index ffd9c9d6fc..b888148841 100644
--- a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
@@ -1,9 +1,9 @@
-module ActiveRecord::Associations::Builder
+module ActiveRecord::Associations::Builder # :nodoc:
   class HasAndBelongsToMany # :nodoc:
-    class JoinTableResolver
+    class JoinTableResolver # :nodoc:
       KnownTable = Struct.new :join_table
 
-      class KnownClass
+      class KnownClass # :nodoc:
         def initialize(lhs_class, rhs_class_name)
           @lhs_class      = lhs_class
           @rhs_class_name = rhs_class_name
@@ -46,7 +46,7 @@ module ActiveRecord::Associations::Builder
 
       join_model = Class.new(ActiveRecord::Base) {
         class << self;
-          attr_accessor :class_resolver
+          attr_accessor :left_model
           attr_accessor :name
           attr_accessor :table_name_resolver
           attr_accessor :left_reflection
@@ -58,25 +58,29 @@ module ActiveRecord::Associations::Builder
         end
 
         def self.compute_type(class_name)
-          class_resolver.compute_type class_name
+          left_model.compute_type class_name
         end
 
         def self.add_left_association(name, options)
-          belongs_to name, options
+          belongs_to name, required: false, **options
           self.left_reflection = _reflect_on_association(name)
         end
 
         def self.add_right_association(name, options)
           rhs_name = name.to_s.singularize.to_sym
-          belongs_to rhs_name, options
+          belongs_to rhs_name, required: false, **options
           self.right_reflection = _reflect_on_association(rhs_name)
         end
 
+        def self.retrieve_connection
+          left_model.retrieve_connection
+        end
+
       }
 
       join_model.name                = "HABTM_#{association_name.to_s.camelize}"
       join_model.table_name_resolver = habtm
-      join_model.class_resolver      = lhs_model
+      join_model.left_model          = lhs_model
 
       join_model.add_left_association :left_side, anonymous_class: lhs_model
       join_model.add_right_association association_name, belongs_to_options(options)