# 5. Validation

DOGs comes with a set of default validators:

{% tabs %}
{% tab title="Any" %}

#### @validated

Requires the annotated field to also validate its properties. By default only the properties of the root object are validated.
{% endtab %}

{% tab title="String" %}

#### @LengthRange()

Specify upper and lower bounds for the string length using the min and max properties.

#### @Regex()

Specify a regex that the string will be matched against. The string is deemed invalid if it doesn't fully match the regex.

#### @email

Requires a valid email address as per a reduced form of RFC 5322 where ip addresses, double quotes and square brackets are omitted.

#### @notBlank

Requires a string that not only consists of whitespace. 
{% endtab %}

{% tab title="Numbers" %}

#### @Range()

Specify upper and lower bounds for the number using the min and max properties. The exclusiveness of the range can be specified by the corresponding properties.

#### @Minimum()

Defines a lower bound for the number. The exclusiveness can be configured using minExclusive-

#### @Maximum()

Defines a upper bound for the number. The exclusiveness can be configured using maxExclusive.

#### @postive

Requires numbers to be greater than zero.

#### @positiveOrZero

Requires numbers to be greater or equal to zero.

#### @negative

Requires numbers to be smaller than zero.

#### @negativeOrZero

Requires numbers to be smaller or equal to zero.
{% endtab %}

{% tab title="Iterable" %}

#### @SizeRange()

Specify upper and lower bounds for the iterables length using the min and max properties.
{% endtab %}
{% endtabs %}

{% hint style="info" %}
Optional/Nullable fields are (for included validators) valid if they are null.
{% endhint %}

To use these validators, import `package:dogs_core/dogs_validation.dart` to the file containing your model.

Validators can be applied to fields by using them as annotations:

```dart
@serializable
class User {  
  @positive // Only ids >=0 are allowed.
  int id;
  
  String name;

  @SizeRange(min: 0, max: 16) // Must only have at max 16 claims
  @Minimum(1) // All claims must be >=1
  List<int>? claims;

  @polymorphic // This is not a validator
  Object? attachment;

  Note(this.text, this.id, this.attachment, this.claims);
}
```

An instance of the previous type can then be validated using the generated extensions on User:

```dart
User user = [...];
bool valid = user.isValid; // Returns if the user is valid
user.validate(); // Throws an exception if the user is invalid.
```

Validation can also be done without using generated extensions:

```dart
User user = [...];
bool valid = dogs.validateObject(user, User); // Returns if the user is valid
dogs.validate<User>(user);  // Throws an exception if the user is invalid.
```