c# - 对可选字段使用数据注释

Question

我有一个可选的字段，但如果它在那里，它必须正好是六个字符长。

StringLength Dataannotation 似乎不允许这样做。有什么方法可以组合事物以获得我想要的东西吗？我理论上可以使用正则表达式，但如果可能的话我想避免这种情况。

Answer 1

Use:

[StringLength(6, MinimumLength = 6)]
public string MyString { get; set; }

With this you're specifying a Maximum of 6 chars and a Minimum of 6 chars. If you enter something below 6, you'll get a message like this one when trying to post the data:

The field MyString must be a string with a minimum length of 6 and a
maximum length of 6.

OR a Regular Expression:

[RegularExpression(@"^.{6,6}$")]
public string MyString { get; set; }

---

There's a way around this by implementing the IValidatableObject interface, but you'll lose the client side/unobtrusive validation. The validation will be done on the server side:

public class MyClass : IValidatableObject
{
    public string MyString { get; set; }
    // ... Other fields ...

    public virtual IEnumerable<ValidationResult> Validate(
                                                 ValidationContext validationContext)
    {
        if (!String.IsNullOrEmpty(MyString))
        {
            if(MyString.Length != 6)
            {
                // ... Validation rules ...
                yield return new ValidationResult("MyString must be 6 chars long",
                                                   new[] { "MyString" });
            }
        }
    }
}