Validation in models

Before we get into the specifics of validation syntax, please keep the following rules in mind:

Validation is defined in the Schema
Validation occurs when a document attempts to be saved, after defaults have been applied.
Mongoose doesn't care about complex error message construction. Errors have type identifiers. For example, "min" is the identifier for the error triggered when a number doesn't meet the minimum value. The path and value that triggered the error can be accessed in the ValidationError object.
Validation is an internal piece of middleware
Validation is asynchronously recursive: when you call Model#save, embedded documents validation is executed. If an error happens, your Model#save callback receives it.

Simple validation

Simple validation is declared by passing a function to validate and an error type to your SchemaType (please read the chapter on model definition to learn more about schemas).

function validator (v) {
  return v.length > 5;
};

new Schema({
    name: { type: String, validate: [validator, 'my error type'] }
})

If you find this syntax too clumsy, you can also define the type

var schema = new Schema({
    name: String
})

and then your validator

schema.path('name').validate(function (v) {
  return v.length > 5;
}, 'my error type');

Regular expressions

If you want to test a certain value against a regular expression:

var schema = new Schema({
    name: { type: String, validate: /[a-z]/ }
});

Asynchronous validation

If you define a validator function with two parameters, like:

schema.path('name').validate(function (v, fn) {
  // my logic
}, 'my error type');

Then the function fn has to be called with true or false, depending on whether the validator passed. This allows for calling other models and querying data asynchronously from your validator.

Built in validators

Strings:

enum: takes a list of allowed values. Example:

var Post = new Schema({
    type: { type: String, enum: ['page', 'post', 'link'] }
})

Numbers:

min: minimum value

var Person = new Schema({
    age: { type: Number, min: 5 }
})

max: maxmimum value

var Person = new Schema({
    age: { type: Number, max: 100 }
})

Mongoose

Validation in models

Simple validation

Regular expressions

Asynchronous validation

Built in validators