The Symfony Validator component includes some advanced constraints such as Callback (to implement custom validation rules), Sequentially (to apply a set of rules in order and interrupt them at any point), Compound (to create a set of reusable constraints), etc.
In Symfony 6.2 we're adding another advanced constraint to that list: When
,
which allows to implement conditional validations.
Consider a Discount
class with two properties:
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// src/Model/Discount.php
namespace App\Model;
class Discount
{
private ?string $type;
private ?int $value;
// ...
}
To validate the object contents, you need to apply these rules:
- If
type
ispercent
, thenvalue
must be less than or equal100
; - If
type
isabsolute
, thenvalue
can be any value; - In all cases, the
value
must be greater than 0.
The new When
constraint defines two main options called expression
and
constraints
. These constraints are only enforced when the result of evaluating
the expression is true
. You can use it as follows to validate that the
value
is less than 100
only if the discount type
is percent
:
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use Symfony\Component\Validator\Constraints as Assert;
// ...
class Discount
{
#[Assert\GreaterThan(0)]
#[Assert\When(
expression: 'this.getType() == "percent"',
constraints: [
new Assert\LessThanOrEqual(100, message: 'The value should be between 1 and 100!')
],
)]
private ?int $value;
// ...
}
The condition passed to the expression
option must use the Symfony
ExpressionLanguage syntax. Inside the expression you can use the this
variable to refer to the object being validated and value
to refer to the
property being valuated (this is only available if you apply the When
constraint to properties).
Finally, you can combine When
with other advanced constraints such as Callback
to define complex conditional validations:
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use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Context\ExecutionContextInterface;
class Discount
{
#[Assert\When(
expression: 'value == "percent"',
constraints: [new Assert\Callback('doComplexValidation')],
)]
private ?string $type;
// ...
}
This is useful although I would hate to write write ExpressionLanguage syntax, it makes it harder to debug and refactor (eg: when the property name changes, searching for references, etc)
When using the Assert\When constrain directly in the form types, would it be possible to use callbacks rather than expressions?
eg
$form->add('type', SomeType::class, [ 'constraints' => [ new Assert\When([ 'expression' => fn (DataClass $data) => $data->getSomeField() === 'some_value', 'constraints' => [...], ], ]);
Typo: "tow" should be "two".
@Tac good catch! It's fixed now.
Love this 🔥
A great addition that will save a lot of time, thanks again! 🙂
@Kevin You can call any method of your entity using an expression: expression: 'this.isCustomConditionMethodValid'
I think, It will be very useful, Good job!