Mongoose accepts null for Number field

Question

I have a mongoose schema where I'm storing a port number. I also have a default value set for the field.

port:{
    type:Number,
    default:1234
}

If I don't get any value via my API, it gets set to 1234. However, If someone sends null, it accepts null and saves to database.

Shouldn't it covert null to 1234? null is not a number! Am I understanding it wrong?

I am considering the solution given here, but I dont want to add extra code for something that should work without it (unless I'm wrong and its not supposed to convert null to 1234)

It's more of a [JavaScript artifact](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/null) that the basics of the "types" in mongoose are based on. So it depends if you can either live with simply throwing an exception ( which you can do with a simple validator ) or supplanting `null` with a "default" value where it is supplied, which is done in "pre" hooks as you mention. Or instead make sure the inputs are `undefined` instead of `null`, and then the "default" just works as expected. — Neil Lunn, Jul 20 '17 at 07:52
Did [my answer](https://stackoverflow.com/questions/45208127/mongoose-accepts-null-for-number-field/45211501#45211501) below help you? Any comments? — rsp, Jul 23 '17 at 12:26

rsp · Accepted Answer · 2017-07-20T10:11:26.363

See the comments in this issue:

https://github.com/Automattic/mongoose/issues/2438

null is a valid value for a Date property, unless you specify required. Defaults only get set if the value is undefined, not if its falsy.

(it's about dates but it can be applied to numbers just as well.)

Your options are to either:

add required to the field
add a custom validator that would reject it
use hooks/middleware to fix the issue

You might get away with a pre-save or post-validate (or some other) hook like this:

YourCollection.pre('save', function (next) {
  if (this.port === null) {
    this.port = undefined;
  }
  next();
});

but probably you'll have to use something like:

YourCollection.pre('save', function (next) {
  if (this.port === null) {
    this.port = 1234; // get it from the schema object instead of hardcoding
  }
  next();
});

See also this answer for some tricks on how to make null trigger default values in function invocation:

Passing in NULL as a parameter in ES6 does not use the default parameter when one is provided

This is unfortunate that Mongoose cannot be configured to tread null as undefined (with some "not-null" parameter or something like that) because it is sometimes the case that you work with data that you got in a request as JSON and it can sometimes convert undefined to null:

> JSON.parse(JSON.stringify([ undefined ]));
[ null ]

or even add null values where there was no (explicit) undefined:

> JSON.parse(JSON.stringify([ 1,,2 ]));
[ 1, null, 2 ]

score 0 · Answer 2 · answered Apr 26 '19 at 10:13

As explained in mongoose official docs here

Number To declare a path as a number, you may use either the Number global constructor or the string 'Number'.

const schema1 = new Schema({ age: Number }); // age will be cast to a Number
const schema2 = new Schema({ age: 'Number' }); // Equivalent

const Car = mongoose.model('Car', schema2);
There are several types of values that will be successfully cast to a Number.

new Car({ age: '15' }).age; // 15 as a Number
new Car({ age: true }).age; // 1 as a Number
new Car({ age: false }).age; // 0 as a Number
new Car({ age: { valueOf: () => 83 } }).age; // 83 as a Number

If you pass an object with a valueOf() function that returns a Number, Mongoose will call it and assign the returned value to the path.

The values null and undefined are not cast.

NaN, strings that cast to NaN, arrays, and objects that don't have a valueOf() function will all result in a CastError.

Mongoose accepts null for Number field

2 Answers2