Validations in Mongoose are defined at the schema level. Validations can be set in both strings and in numbers. Mongoose provides us with built-in validation techniques for strings and numbers. Also, we can customize these according to our need as well. Since validations are defined in the schemas, they are triggered when we hit the save() method for any document. If we only want to test these validations, we can do that as well by executing the validation method only via {doc}.validate().
validate() is also middleware, which means it has control when we are executing some methods in an asynchronous way.
