Question

我想确保我的模型的list属性不为空，因此我创建了 ValidationAttribute ，但值为List＆lt; long＆gt; 始终返回null，即使用 NoEmpty 修饰的属性的类型为List＆lt;长＆gt;。

为什么呢？以及如何正确地做到这一点？

public class NoEmptyAttribute: ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var list = value as List<long>;

        var msg = $"{validationContext.MemberName} can not bt empty";

        if (list == null) return new ValidationResult(msg);

        return list.Count == 0 ? new ValidationResult(msg) : ValidationResult.Success; 
    }
}

我更新了我的代码，现在工作正常：

public class NoEmptyAttribute: ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        var list = value as IEnumerable;

        var msg = $"{validationContext.MemberName} can not be null";

        if (list == null) return new ValidationResult(msg);

        return list.Cast<object>().Any() ? ValidationResult.Success : new ValidationResult(msg);
    }
}

为什么值为List＆lt; long＆gt; 总是返回null，该值的类型为HashSet＆lt;长＆gt;。

Answer 1

我写了一个单元测试（基于你的NoEmptyAttribute的代码），一切都按预期工作

[TestClass()]
public class NoEmptyAttributeTests
{
    [TestMethod]
    public void GetValidationResult_ListLongWithElements_ReturnsNull()
    {
        object obj = new object();
        object value = new List<long> { 1, 2 };

        ValidationContext ctx = new ValidationContext( obj ) { MemberName = "Foo" };
        var noempty = new NoEmptyAttribute();
        var result = noempty.GetValidationResult( value, ctx );
        Assert.IsNull( result );
    }

    [TestMethod]
    public void GetValidationResult_ListLongEmpty_ReturnsCannotBeEmpty()
    {
        object obj = new object();
        object value = new List<long>();

        ValidationContext ctx = new ValidationContext( obj ) { MemberName = "Foo" };
        var noempty = new NoEmptyAttribute();
        var result = noempty.GetValidationResult( value, ctx );
        Assert.IsNotNull( result );
        Assert.AreEqual( "Foo can not bt empty", result.ErrorMessage );
    }

    [TestMethod]
    public void GetValidationResult_ListLongNull_ReturnsCannotBeEmpty()
    {
        object obj = new object();
        object value = null;

        ValidationContext ctx = new ValidationContext( obj ) { MemberName = "Foo" };
        var noempty = new NoEmptyAttribute();
        var result = noempty.GetValidationResult( value, ctx );
        Assert.IsNotNull( result );
        Assert.AreEqual( "Foo can not bt empty", result.ErrorMessage );
    }
}

对象作为List <long>始终返回null

1 个答案: