Before we get into the specifics of validation syntax, please keep the following rules in mind:
- Validation is defined in the SchemaType
- Validation is middleware. Mongoose registers validation as a
pre('save')
hook on every schema by default. - You can disable automatic validation before save by setting the validateBeforeSave option
- You can manually run validation using
doc.validate(callback)
ordoc.validateSync()
- You can manually mark a field as invalid (causing validation to fail) by using
doc.invalidate(...)
- Validators are not run on undefined values. The only exception is the
required
validator. - Validation is asynchronously recursive; when you call Model#save, sub-document validation is executed as well. If an error occurs, your Model#save callback receives it
- Validation is customizable
[require:Validation$]
- Built-in Validators
- Custom Error Messages
- The
unique
Option is Not a Validator - Custom Validators
- Async Custom Validators
- Validation Errors
- Cast Errors
- Global SchemaType Validation
- Required Validators On Nested Objects
- Update Validators
- Update Validators and
this
- Update Validators Only Run On Updated Paths
- Update Validators Only Run For Some Operations
Mongoose has several built-in validators.
- All SchemaTypes have the built-in required validator. The required validator uses the SchemaType's
checkRequired()
function to determine if the value satisfies the required validator. - Numbers have
min
andmax
validators. - Strings have
enum
,match
,minLength
, andmaxLength
validators.
Each of the validator links above provide more information about how to enable them and customize their error messages.
[require:Built-in Validators]
You can configure the error message for individual validators in your schema. There are two equivalent ways to set the validator error message:
- Array syntax:
min: [6, 'Must be at least 6, got {VALUE}']
- Object syntax:
enum: { values: ['Coffee', 'Tea'], message: '{VALUE} is not supported' }
Mongoose also supports rudimentary templating for error messages.
Mongoose replaces {VALUE}
with the value being validated.
[require:Custom Error Messages]
A common gotcha for beginners is that the unique
option for schemas
is not a validator. It's a convenient helper for building MongoDB unique indexes.
See the FAQ for more information.
[require:The `unique` Option is Not a Validator]
If the built-in validators aren't enough, you can define custom validators to suit your needs.
Custom validation is declared by passing a validation function.
You can find detailed instructions on how to do this in the
SchemaType#validate()
API docs.
[require:Custom Validators]
Custom validators can also be asynchronous. If your validator function
returns a promise (like an async
function), mongoose will wait for that
promise to settle. If the returned promise rejects, or fulfills with
the value false
, Mongoose will consider that a validation error.
[require:Async Custom Validators]
Errors returned after failed validation contain an errors
object
whose values are ValidatorError
objects. Each
ValidatorError has kind
, path
,
value
, and message
properties.
A ValidatorError also may have a reason
property. If an error was
thrown in the validator, this property will contain the error that was
thrown.
[require:Validation Errors]
Before running validators, Mongoose attempts to coerce values to the
correct type. This process is called casting the document. If
casting fails for a given path, the error.errors
object will contain
a CastError
object.
Casting runs before validation, and validation does not run if casting
fails. That means your custom validators may assume v
is null
,
undefined
, or an instance of the type specified in your schema.
[require:Cast Errors]
In addition to defining custom validators on individual schema paths, you can also configure a custom validator to run on every instance of a given SchemaType
.
For example, the following code demonstrates how to make empty string ''
an invalid value for all string paths.
[require:Global SchemaType Validation]
Defining validators on nested objects in mongoose is tricky, because nested objects are not fully fledged paths.
[require:Required Validators On Nested Objects]
In the above examples, you learned about document validation. Mongoose also
supports validation for update()
,
updateOne()
,
updateMany()
,
and findOneAndUpdate()
operations.
Update validators are off by default - you need to specify
the runValidators
option.
To turn on update validators, set the runValidators
option for
update()
, updateOne()
, updateMany()
, or findOneAndUpdate()
.
Be careful: update validators are off by default because they have several
caveats.
[require:Update Validators$]
There are a couple of key differences between update validators and
document validators. In the color validation function below, this
refers
to the document being validated when using document validation.
However, when running update validators, the document being updated
may not be in the server's memory, so by default the value of this
is
not defined.
[require:Update Validators and `this`]
The other key difference is that update validators only run on the paths specified in the update. For instance, in the below example, because 'name' is not specified in the update operation, update validation will succeed.
When using update validators, required
validators only fail when
you try to explicitly $unset
the key.
[require:Update Validators Only Run On Updated Paths]
One final detail worth noting: update validators only run on the following update operators:
$set
$unset
$push
$addToSet
$pull
$pullAll
For instance, the below update will succeed, regardless of the value of
number
, because update validators ignore $inc
.
Also, $push
, $addToSet
, $pull
, and $pullAll
validation does
not run any validation on the array itself, only individual elements
of the array.
[require:Update Validators Only Run For Some Operations]
Now that we've covered Validation
, let's take a look at Middleware.