如何直接针对 List<T> 进行验证？答案

【问题标题】：How to validate directly against a List<T>?如何直接针对 List<T> 进行验证？
【发布时间】：2017-08-10 21:28:32
【问题描述】：

我有一个模型类：

public class MyModel() { //properties here... }

我想验证MyModel 对象的列表。所以我创建了这个验证器：

class MyModelListValidator : AbstractValidator<List<MyModel>>
{
    public MyModelListValidator ()
    {
        RuleFor(x => x)
            .SetCollectionValidator(new MyModelValidator())
            .When(x => x != null);
    }

    private class MyModelValidator : AbstractValidator<MyModel>
    {
        public MyModelValidator()
        {
            //MyModel property validation here...
        }
    }
}

但以上不起作用。另一种方法是创建一个类：

public class MyModelList()
{
    public List<MyModel> Items { get; set; }
}

这会奏效。

但是有没有办法在不使用这个附加类的情况下做到这一点？

【问题讨论】：

如果你的action得到List<MyModel>作为参数，你可以定义AbstractValidator<MyModel>，fluentvalidation会自动将它应用到列表中的每一项。

标签： c# fluentvalidation

【解决方案1】：

如果您使用数据注释来执行验证，您可能需要一个自定义属性：

public class EnsureOneElementAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        var list = value as IList;
        if (list != null)
        {
            return list.Count > 0;
        }
        return false;
    }
}

然后：

[EnsureOneElement(ErrorMessage = "At least a person is required")]
public List<Person> Persons { get; private set; }
or to make it more generic:

public class EnsureMinimumElementsAttribute : ValidationAttribute
{
    private readonly int _minElements;
    public EnsureMinimumElementsAttribute(int minElements)
    {
        _minElements = minElements;
    }

    public override bool IsValid(object value)
    {
        var list = value as IList;
        if (list != null)
        {
            return list.Count >= _minElements;
        }
        return false;
    }
}

然后：

[EnsureMinimumElements(1, ErrorMessage = "At least a person is required")]
public List<Person> Persons { get; private set; }
Personally I use FluentValidation.NET instead of Data Annotations to perform validation because I prefer the imperative validation logic instead of the declarative. I think it is more powerful. So my validation rule would simply look like this:

RuleFor(x => x.Persons)
    .Must(x => x.Count > 0)
    .WithMessage("At least a person is required");

【讨论】：