ASP.NET Core MVC Model验证添加

>自定义验证 Attribute

• Attribute，IModelValidator


示例：ValidUrlAttribute

public class ValidUrlAttribute : Attribute, IModelValidator
{
    public string ErrorMessage { get; set; }
    public IEnumerable<ModelValidationResult> Validate(
        ModelValidationContext context)
    {
        var url = context.Model as string;
        if (url != null && Uri.IsWellFormedUriString(url, UriKind.Absolute))
        {
            return Enumerable.Empty<ModelValidationResult>();
        }
        return new List<ModelValidationResult>
        {
            new ModelValidationResult(string.Empty, ErrorMessage)
        };
    }
}

使用时标注在 ViewModel 等实体类的属性上即可：
[Display(Name = "封面地址")]
[Required(ErrorMessage = "{0}是必填项"), MaxLength(200, ErrorMessage = "{0}的长度不可超过{1}")]
//[DataType(DataType.Url)]
[ValidUrl(ErrorMessage = "这个URL不正确")]
public string CoverUrl { get; set; }

远程验证
• [Remote]
• 客户端调用 Action 方法进行验证（前台调用后台验证）
Action 中的方法：
[AcceptVerbs("Get", "Post")]
public async Task CheckRoleExist([Bind("RoleName")]string roleName)
{
var role = await _roleManager.FindByNameAsync(roleName);
if (role != null) return Json("角色已经存在了");
return Json(true);
}
标注属性：

public class RoleAddViewModel
{
[Required]
[Display(Name = "角色名称")]
[Remote(nameof(RoleController.CheckRoleExist), "Role", ErrorMessage = "角色已存在")]
public string RoleName { get; set; }
}