respect-validation/docs/rules/KeyExists.md
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# KeyExists
- `KeyExists(int|string $key)`
Validates if the given key exists in an array.
```php
v::keyExists('name')->isValid(['name' => 'The Respect Panda']); // true
v::keyExists('name')->isValid(['email' => 'therespectpanda@gmail.com']); // false
v::keyExists(0)->isValid(['a', 'b', 'c']); // true
v::keyExists(4)->isValid(['a', 'b', 'c']); // false
v::keyExists('username')->isValid(new ArrayObject(['username' => 'therespectpanda'])); // true
v::keyExists(5)->isValid(new ArrayObject(['a', 'b', 'c'])); // false
```
## Notes
- To validate an array against a given rule if the key exists, use [KeyOptional](KeyOptional.md) instead.
- To validate an array against a given rule requiring the key to exist, use [Key](Key.md) instead.
## Templates
### `KeyExists::TEMPLATE_STANDARD`
| Mode | Template |
| ---------- | ------------------------------- |
| `default` | {{subject}} must be present |
| `inverted` | {{subject}} must not be present |
## Template placeholders
| Placeholder | Description |
| ----------- | ---------------------------------------------------------------- |
| `subject` | The validated input or the custom validator name (if specified). |
## Caveats
`KeyExists` defines the given `$key` as the path, and because it is a standalone rule without children, it's not possible to display a fully custom name with it.
When no custom name is set, the path is displayed as `{{name}}`. When a custom name is set, the validation engine prepends the path to the custom name:
```php
v::keyExists('foo')->assert([]);
// Message: `.foo` must be present
v::keyExists('foo')->setName('Custom name')->assert([]);
// Message: `.foo` (<- Custom name) must be present
```
If you want to display only a custom name while checking if a key exists, use [Key](Key.md) with [AlwaysValid](AlwaysValid.md):
```php
v::key('foo', v::alwaysValid()->setName('Custom name'))->assert([]);
// Message: Custom name must be present
```
## Categorization
- Arrays
- Structures
## Changelog
| Version | Description |
| ------: | -------------------------- |
| 3.0.0 | Created from [Key](Key.md) |
---
See also:
- [AlwaysValid](AlwaysValid.md)
- [ArrayType](ArrayType.md)
- [ArrayVal](ArrayVal.md)
- [Each](Each.md)
- [Key](Key.md)
- [KeyOptional](KeyOptional.md)
- [Property](Property.md)
- [PropertyExists](PropertyExists.md)
- [PropertyOptional](PropertyOptional.md)