respect-validation/docs/rules/KeyOptional.md
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# KeyOptional
- `KeyOptional(int|string $key, Rule $rule)`
Validates the value of an array against a given rule when the key exists.
```php
v::keyOptional('name', v::stringType())->isValid([]); // true
v::keyOptional('name', v::stringType())->isValid(['name' => 'The Respect Panda']); // true
v::keyOptional('email', v::email())->isValid([]); // true
v::keyOptional('email', v::email())->isValid(['email' => 'therespectpanda@gmail.com']); // true
v::keyOptional('age', v::intVal())->isValid(['age' => 'Twenty-Five']); // false
```
The name of this validator is automatically set to the key name.
```php
v::keyOptional('age', v::intVal())->assert(['age' => 'Twenty-Five']);
// message: age must be an integer number
```
## Note
This rule will pass for anything that is not an array because it will always pass when it doesn't find a key. If you
want to ensure the input is an array, use [ArrayType](ArrayType.md) with it.
```php
v::arrayType()->keyOptional('phone', v::phone())->assert('This is not an array');
// message: "This is not an array" must be of type array
```
Below are some other rules that are tightly related to `KeyOptional`:
- To validate if a key exists, use [KeyExists](KeyExists.md) instead.
- To validate an array against a given rule requiring the key to exist, use [Key](Key.md) instead.
## Templates
## Template placeholders
| Placeholder | Description |
| ----------- | ---------------------------------------------------------------- |
| `subject` | The validated input or the custom validator name (if specified). |
## Categorization
- Arrays
- Structures
## Changelog
| Version | Description |
| ------: | -------------------------- |
| 3.0.0 | Created from [Key](Key.md) |
---
See also:
- [ArrayType](ArrayType.md)
- [ArrayVal](ArrayVal.md)
- [Each](Each.md)
- [Key](Key.md)
- [KeyExists](KeyExists.md)
- [Property](Property.md)
- [PropertyExists](PropertyExists.md)
- [PropertyOptional](PropertyOptional.md)
[array]: https://www.php.net/array
[ArrayAccess]: https://www.php.net/arrayaccess