New in Symfony 3.4: Improved comparison constraints

Contributed by Maxime Steinhausser in #22576

The original purpose of comparison constraints was to validate properties against some predefined value (e.g. "the price must be greater than 0", "the age must be greater or equal than 18", etc.)

However, in Symfony applications is common to compare the value of object properties between them (e.g. "the end date is greater than the start date", "the plain password is not identical to the login", etc.)

In those cases, you can use the Expression constraint to define a expression that compares both properties:

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use Symfony\Component\Validator\Constraints as Assert;

class Event
{
    /** @Assert\DateTime() */
    private $startDate;

    /**
     * @Assert\DateTime()
     * @Assert\Expression("value > this.startDate")
     */
    private $endDate;

    // ...
}

In Symfony 3.4, we improved the comparison expressions to accept a new option called propertyPath which defines the path of the property whose value you want to compare with:

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use Symfony\Component\Validator\Constraints as Assert;

class Event
{
    /** @Assert\DateTime() */
    private $startDate;

    /**
     * @Assert\DateTime()
     * @Assert\GreaterThan(propertyPath="startDate")
     */
    private $endDate;

    // ...
}

The value of the propertyPath option can be any valid PropertyAccess component notation, so you can refer to properties of embedded objects too.