# File lib/mongoid/relations/bindings/referenced/many_to_many.rb, line 19
          def bind_one(doc)
            unless _binding?
              _binding do
                inverse_keys = doc.you_must(metadata.inverse_foreign_key)
                inverse_keys.push(base.id) if inverse_keys
                base.synced[metadata.foreign_key] = true
                doc.synced[metadata.inverse_foreign_key] = true
              end
            end
          end