自定义DataAnnotation IsValid未调用

Question

背景

大家好,

基本上,我在.NET核类库中编写自定义数据注释,它将验证IEnumerable至少具有一定数量的元素.

---

问题

出于某种原因,在运行验证时,永远不会调用IsValid.我已经找到了一些关于这个问题的其他SO问题,但它们都有一个与我不同的问题(基本上,它们实际上并没有验证它们的对象).但是,我正在验证我的对象(调用Validator.TryValidateObject(...)),然而,从未调用过IsValid.

如果我使用任何开箱即用的验证属性(例如必需),它将按预期运行.

---

代码

MinElementsAttribute.cs

public class MinElementsAttribute : ValidationAttribute
{
    readonly int minElements;

    public MinElementsAttribute(int minElements) : base($"Collection must have a size of at least {minElements}")
    {
        this.minElements = minElements;
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var list = value as IEnumerable<object>;

        if(list == null || list.Count() < this.minElements)
        {
            return new ValidationResult(this.FormatErrorMessage(validationContext.DisplayName));
        }

        return ValidationResult.Success;
    }
}

MinElementsTests.cs

[Fact]
public void TestValidation()
{
    var validationResults = new List<ValidationResult>();
    var testObject = new TestObject();

    // Should be false since I have not added anything to the list
    var isValid = Validator.TryValidateObject(testObject, new ValidationContext(testObject), validationResults);

    // Fails since isValid comes back as true because IsValid on MinElementsAttribute is never called
    Assert.False(isValid);
    Assert.NotEmpty(validationResults);
}

internal class TestObject
{
    public TestObject()
    {
        this.StringList = new List<string>();
    }

    [MinElements(3)]
    public List<string> StringList { get; set; }
}

---

编辑:解决方案

请参阅解决方案的已接受答案.我想补充一点,还要注意,通过将继承更改为RequiredAttribute而不是ValidationAttribute,可以隐式强制执行所有对象属性的验证.

Answer 1

Validator.TryValidateObjectclass有一些重载方法.你想使用这个:

public static bool TryValidateObject(object instance, ValidationContext validationContext, ICollection<ValidationResult> validationResults, bool validateAllProperties);

来自MSDN文章:

validateAllProperties
类型:System.Boolean
如果为true,则验证所有属性; 如果为false,则仅验证所需的属性.

您必须使用此方法,因为您的属性不是从RequiredAttribute类派生的.

我的样本

var validationResults = new List<ValidationResult>();            
var testObject = new TestObject();
ValidationContext contexts = new ValidationContext(testObject, null, null);            
var isValid = Validator.TryValidateObject(testObject, contexts, validationResults, true);