Mongoose - How can I throw more than one error in pre (save/update) middleware?

I have some pre save and update hooks in a model and I need to show all the errors of validations at same time.

There is in the documentation this information about next function:

> Calling next() multiple times is a no-op. If you call next() with an error err1 and then throw an error err2, mongoose will report err1.

See the reference here

I want to do something like the code below to return two or more validation errors, but like the documentation only the first error is thrown

<!-- language: lang-js -->

Schema.pre('save', function(next) {
  if (this.prop1 == 'foo')
    next(new Error('Error one'))
  
  if (this.prop2 == 'bar')
    next(new Error('Error two'))
})

<!-- end snippet -->

How can I do it? Is there an alternative?

You can add your errors into an array, and then at the end if the length of the array is greater than 0, you can send one error message by joining errors.

Schema.pre("save", function(next) {
  let validationErrors = [];

  if (this.prop1 == "foo") validationErrors.push("Error one");

  if (this.prop2 == "bar") validationErrors.push("Error two");

  if (validationErrors.length > 0) {
    next(new Error(validationErrors.join(",")));
  }

  next();
});

But generally we don't use this kind of validation. If you are already using mongoose, you can use its validation features.

Some of the other validation packages are:

1. Express Validator
2. Joi

Hello Daniel welcome to Stack Overflow!

My approach would be to save the errors into an iterable and send down the iterable as the error object (or stringify with join() the whole thing if it accepts strings only.

Please check if this handles your issue, I don't know of any built-in ways of achieving your end result.

Schema.pre('save', function(next) {
  const errors = [];

  if (this.prop1 == 'foo')
    errors.push('Error one');
    
  if (this.prop2 == 'bar')
    errors.push('Error two');

  if (this.prop1 == 'foo' || this.prop2 == 'bar') next(new Error(errors))
})