MVC如果确认字段不为空，则比较电子邮件

Question

只有当字段不为空时，是否有办法触发比较数据注释？如果没有，那么另一种方法是什么？

以下代码始终触发比较数据注释，无论它是否具有值。

[EmailAddress]
[Required]
[Display(Name = "Email Address")]
public string EmailAddress { get; set; }

[Display(Name = "Confirm Email Address")]
[Compare("EmailAddress", ErrorMessage = "The email addresses do not match.")]
public string ConfirmEmailAddress { get; set; }

Answer 1

使用您自己的属性扩展属性可能最简单：

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public sealed class CompareEnhancedAttribute : CompareAttribute
{
    public bool AllowEmptyStrings { get; set; }

    public CompareEnhancedAttribute(string otherProperty)
        : base(otherProperty)
    {
    }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (AllowEmptyStrings && string.IsNullOrEmpty(value?.ToString()))
        {
            return ValidationResult.Success;
        }
        else
        {
            return base.IsValid(value, validationContext);
        }
    }
}

然后像这样使用它：

public sealed class ContactModel
{
    /* omitted other attributes */

    public string EmailAddress { get; set; }

    [CompareEnhanced("EmailAddress", AllowEmptyStrings = true)]
    public string ConfirmEmailAddress { get; set; }
}