空白

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验证值是否为空白 - 意味着等于空字符串或 null

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        if ('' !== $value && null !== $value) {
    // validation will fail
}
    

要强制值必须严格等于 null，请参阅 IsNull 约束。

要强制值不为空白，请参阅 NotBlank。但请注意，NotBlank 并非 Blank 的严格反义词。

应用于	属性或方法
类	空白
验证器	BlankValidator

基本用法

如果出于某种原因，您想确保 Author 类的 firstName 属性为空白，您可以执行以下操作

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        // src/Entity/Author.php
namespace App\Entity;

use Symfony\Component\Validator\Constraints as Assert;

class Author
{
    #[Assert\Blank]
    protected string $firstName;
}
    

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        # config/validator/validation.yaml
App\Entity\Author:
    properties:
        firstName:
            - Blank: ~
    

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        <!-- config/validator/validation.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<constraint-mapping xmlns="http://symfony.ac.cn/schema/dic/constraint-mapping"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.ac.cn/schema/dic/constraint-mapping http://symfony.ac.cn/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">

    <class name="App\Entity\Author">
        <property name="firstName">
            <constraint name="Blank"/>
        </property>
    </class>
</constraint-mapping>
    

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        // src/Entity/Author.php
namespace App\Entity;

use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Mapping\ClassMetadata;

class Author
{
    public static function loadValidatorMetadata(ClassMetadata $metadata): void
    {
        $metadata->addPropertyConstraint('firstName', new Assert\Blank());
    }
}
    