📐 Nette Schema: validating data structures against a given Schema.

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v1.2.3 2022-10-13 01:24 UTC

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Last update: 2023-06-05 11:37:07 UTC


Nette Schema

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A practical library for validation and normalization of data structures against a given schema with a smart & easy-to-understand API.

Documentation can be found on the website.


composer require nette/schema

It requires PHP version 8.0 and supports PHP up to 8.2.

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Basic Usage

In variable $schema we have a validation schema (what exactly this means and how to create it we will say later) and in variable $data we have a data structure that we want to validate and normalize. This can be, for example, data sent by the user through an API, configuration file, etc.

The task is handled by the Nette\Schema\Processor class, which processes the input and either returns normalized data or throws an Nette\Schema\ValidationException exception on error.

$processor = new Nette\Schema\Processor;

try {
	$normalized = $processor->process($schema, $data);
} catch (Nette\Schema\ValidationException $e) {
	echo 'Data is invalid: ' . $e->getMessage();

Method $e->getMessages() returns array of all message strings and $e->getMessageObjects() return all messages as Nette\Schema\Message objects.

Defining Schema

And now let's create a schema. The class Nette\Schema\Expect is used to define it, we actually define expectations of what the data should look like. Let's say that the input data must be a structure (e.g. an array) containing elements processRefund of type bool and refundAmount of type int.

use Nette\Schema\Expect;

$schema = Expect::structure([
    'processRefund' => Expect::bool(),
    'refundAmount' => Expect::int(),

We believe that the schema definition looks clear, even if you see it for the very first time.

Lets send the following data for validation:

$data = [
    'processRefund' => true,
    'refundAmount' => 17,

$normalized = $processor->process($schema, $data); // OK, it passes

The output, i.e. the value $normalized, is the object stdClass. If we want the output to be an array, we add a cast to schema Expect::structure([...])->castTo('array').

All elements of the structure are optional and have a default value null. Example:

$data = [
    'refundAmount' => 17,

$normalized = $processor->process($schema, $data); // OK, it passes
// $normalized = {'processRefund' => null, 'refundAmount' => 17}

The fact that the default value is null does not mean that it would be accepted in the input data 'processRefund' => null. No, the input must be boolean, i.e. only true or false. We would have to explicitly allow null via Expect::bool()->nullable().

An item can be made mandatory using Expect::bool()->required(). We change the default value to false using Expect::bool()->default(false) or shortly using Expect::bool(false).

And what if we wanted to accept 1 and 0 besides booleans? Then we list the allowed values, which we will also normalize to boolean:

$schema = Expect::structure([
    'processRefund' => Expect::anyOf(true, false, 1, 0)->castTo('bool'),
    'refundAmount' => Expect::int(),

$normalized = $processor->process($schema, $data);
is_bool($normalized->processRefund); // true

Now you know the basics of how the schema is defined and how the individual elements of the structure behave. We will now show what all the other elements can be used in defining a schema.

Data Types: type()

All standard PHP data types can be listed in the schema:

Expect::string($default = null)
Expect::int($default = null)
Expect::float($default = null)
Expect::bool($default = null)
Expect::array($default = [])

And then all types supported by the Validators via Expect::type('scalar') or abbreviated Expect::scalar(). Also class or interface names are accepted, e.g. Expect::type('AddressEntity').

You can also use union notation:


The default value is always null except for array and list, where it is an empty array. (A list is an array indexed in ascending order of numeric keys from zero, that is, a non-associative array).

Array of Values: arrayOf() listOf()

The array is too general structure, it is more useful to specify exactly what elements it can contain. For example, an array whose elements can only be strings:

$schema = Expect::arrayOf('string');

$processor->process($schema, ['hello', 'world']); // OK
$processor->process($schema, ['a' => 'hello', 'b' => 'world']); // OK
$processor->process($schema, ['key' => 123]); // ERROR: 123 is not a string

The list is an indexed array:

$schema = Expect::listOf('string');

$processor->process($schema, ['a', 'b']); // OK
$processor->process($schema, ['a', 123]); // ERROR: 123 is not a string
$processor->process($schema, ['key' => 'a']); // ERROR: is not a list
$processor->process($schema, [1 => 'a', 0 => 'b']); // ERROR: is not a list

The parameter can also be a schema, so we can write:


The default value is an empty array. If you specify default value and call mergeDefaults(), it will be merged with the passed data.

Enumeration: anyOf()

anyOf() is a set of values ​​or schemas that a value can be. Here's how to write an array of elements that can be either 'a', true, or null:

$schema = Expect::listOf(
	Expect::anyOf('a', true, null)

$processor->process($schema, ['a', true, null, 'a']); // OK
$processor->process($schema, ['a', false]); // ERROR: false does not belong there

The enumeration elements can also be schemas:

$schema = Expect::listOf(
	Expect::anyOf(Expect::string(), true, null)

$processor->process($schema, ['foo', true, null, 'bar']); // OK
$processor->process($schema, [123]); // ERROR

The default value is null.


Structures are objects with defined keys. Each of these key => value pairs is referred to as a "property":

Structures accept arrays and objects and return objects stdClass (unless you change it with castTo('array'), etc.).

By default, all properties are optional and have a default value of null. You can define mandatory properties using required():

$schema = Expect::structure([
	'required' => Expect::string()->required(),
	'optional' => Expect::string(), // the default value is null

$processor->process($schema, ['optional' => '']);
// ERROR: item 'required' is missing

$processor->process($schema, ['required' => 'foo']);
// OK, returns {'required' => 'foo', 'optional' => null}

Although null is the default value of the optional property, it is not allowed in the input data (the value must be a string). Properties accepting null are defined using nullable():

$schema = Expect::structure([
	'optional' => Expect::string(),
	'nullable' => Expect::string()->nullable(),

$processor->process($schema, ['optional' => null]);
// ERROR: 'optional' expects to be string, null given.

$processor->process($schema, ['nullable' => null]);
// OK, returns {'optional' => null, 'nullable' => null}

By default, there can be no extra items in the input data:

$schema = Expect::structure([
	'key' => Expect::string(),

$processor->process($schema, ['additional' => 1]);
// ERROR: Unexpected item 'additional'

Which we can change with otherItems(). As a parameter, we will specify the schema for each extra element:

$schema = Expect::structure([
	'key' => Expect::string(),

$processor->process($schema, ['additional' => 1]); // OK
$processor->process($schema, ['additional' => true]); // ERROR


You can deprecate property using the deprecated([string $message]) method. Deprecation notices are returned by $processor->getWarnings() (since v1.1):

$schema = Expect::structure([
	'old' => Expect::int()->deprecated('The item %path% is deprecated'),

$processor->process($schema, ['old' => 1]); // OK
$processor->getWarnings(); // ["The item 'old' is deprecated"]

Ranges: min() max()

Use min() and max() to limit the number of elements for arrays:

// array, at least 10 items, maximum 20 items

For strings, limit their length:

// string, at least 10 characters long, maximum 20 characters

For numbers, limit their value:

// integer, between 10 and 20 inclusive

Of course, it is possible to mention only min(), or only max():

// string, maximum 20 characters

Regular Expressions: pattern()

Using pattern(), you can specify a regular expression which the whole input string must match (i.e. as if it were wrapped in characters ^ a $):

// just 9 digits

Custom Assertions: assert()

You can add any other restrictions using assert(callable $fn).

$countIsEven = function ($v) { return count($v) % 2 === 0; };

$schema = Expect::arrayOf('string')
	->assert($countIsEven); // the count must be even

$processor->process($schema, ['a', 'b']); // OK
$processor->process($schema, ['a', 'b', 'c']); // ERROR: 3 is not even


Expect::string()->assert('is_file'); // the file must exist

You can add your own description for each assertions. It will be part of the error message.

$schema = Expect::arrayOf('string')
	->assert($countIsEven, 'Even items in array');

$processor->process($schema, ['a', 'b', 'c']);
// Failed assertion "Even items in array" for item with value array.

The method can be called repeatedly to add more assertions.

Mapping to Objects: from()

You can generate structure schema from the class. Example:

class Config
	/** @var string */
	public $name;
	/** @var string|null */
	public $password;
	/** @var bool */
	public $admin = false;

$schema = Expect::from(new Config);

$data = [
	'name' => 'jeff',

$normalized = $processor->process($schema, $data);
// $normalized instanceof Config
// $normalized = {'name' => 'jeff', 'password' => null, 'admin' => false}

If you are using PHP 7.4 or higher, you can use native types:

class Config
	public string $name;
	public ?string $password;
	public bool $admin = false;

$schema = Expect::from(new Config);

Anonymous classes are also supported:

$schema = Expect::from(new class {
	public string $name;
	public ?string $password;
	public bool $admin = false;

Because the information obtained from the class definition may not be sufficient, you can add a custom schema for the elements with the second parameter:

$schema = Expect::from(new Config, [
	'name' => Expect::string()->pattern('\w:.*'),

Casting: castTo()

Successfully validated data can be cast:


In addition to native PHP types, you can also cast to classes:


Normalization: before()

Prior to the validation itself, the data can be normalized using the method before(). As an example, let's have an element that must be an array of strings (eg ['a', 'b', 'c']), but receives input in the form of a string a b c:

$explode = function ($v) { return explode(' ', $v); };

$schema = Expect::arrayOf('string')

$normalized = $processor->process($schema, 'a b c');
// OK, returns ['a', 'b', 'c']