# Validation

You can validate incoming data based on a set of rules. One example validator is supplied, the [Validation rules validator](#validation-rules).

You can create a custom validator by implementing the `Strata\Data\Validate\ValidatorInterface` interface. This requires a `isValid()` method to test whether data is valid and a `getErrorMessage()` method to return the error message for the last validation attempt.

The basic flow is:

* Instantiate the validator object
* Call the `isValid($data)` method, passing the data array or object you are validating
* Return any error message via `getErrorMessage()`
* Take any action you wish based on the validation result

```php
$validator = new CustomValidator();

if ($validator->isValid($data)) {
    // do something
}
```

## Validation rules

A simple validation rules system exists, inspired by [Laravel's Validation](https://laravel.com/docs/validation).

Simply create a new instance of `Strata\Data\Validate\ValidationRules` and pass in the validation requirements in the constructor. This is an array made up of the property path to the field you want to validate and the validation rule. See [how to write property paths](/data/retrieving-data/property-paths.md).

The rules format is:

```
'[data property]' => 'rule|another rule:values separated by commas'
```

E.g.

```php
$rules = [
    '[total]'         => 'required|integer', 
    '[data][title]'   => 'required',
    '[data][type]'    => 'required|in:1,2,3',
];
```

In this example:

* `$item['total']` must exist and be an integer.
* `$item['data']['title']` must exist.
* `$item['data']['type']` must exist and have a value of: 1, 2, 3.

A complete example:

```php
$validator = new ValidationRules([
    '[total]'         => 'required|integer', 
    '[data][title]'   => 'required',
    '[data][type]'    => 'required|in:1,2,3',
];

if ($validator->isValid($item)) {
    // do something
}
```

Available validation rules:

* [array](#array)
* [boolean](#boolean)
* [email](#email)
* [image](#image)
* [in](#in)
* [number](#number)
* [required](#required)
* [url](#url)

### array

Tests whether the property is an array.

### boolean

Tests whether the property is "1", "true", "on" and "yes". Returns false otherwise.

### email

Tests whether the property is a valid email address.

### image

Tests whether the property is an image filename (jpg, jpeg, png, bmp, gif, svg, or webp).

### in

Tests whether the property value is one of the allowed passed values. For example, a rule of `in:1,2,3` tests for whether the property value is 1, 2, or 3.

### number

Tests whether the property is a number, using PHP's [is\_numeric()](https://www.php.net/is-numeric) rules.

### required

Tests whether the property exists and is non-empty. Empty is defined as null, an empty array or an empty string.

### url

Tests whether the property is a valid URL.

### Custom validation rules

You can also define your own custom validation rule by creating a class that implements the `Strata\Data\Validate\RuleInterface` interface. It is recommended to extend `Strata\Data\Validate\Rule\ValidatorRuleAbstract` which makes building custom rules easier.

To use a custom validation rule pass an instance of the class as the rule:

```php
$validator = new ValidationRules([
    'total'         => 'required|integer',
    'data.title'    => new CustomRuleValidation(),
];
```


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