问题描述
我创建了一个想要用于我的API控制器DTO的自定义验证属性。此属性需要配置的选项中的值，这就是为什么要将它们注入构造函数中的原因，以便以后可以在IsValid和FormatErrorMessage方法中使用options服务。
internal class MyValidationAttribute : ValidationAttribute
{
private readonly IOptionsMonitor<MyOptions> myOptionsMonitor;
public MyValidationAttribute(IOptionsMonitor<MyOptions> myOptionsMonitor)
{
this.myOptionsMonitor = myOptionsMonitor;
}
public override bool IsValid(object value)
{
// ... use myOptionsMonitor here ...
return false;
}
public override string FormatErrorMessage(string name)
{
// ... use myOptionsMonitor here ...
return string.Empty;
}
}
不幸的是，当我要将其用作我的DTO中的属性
internal class MyDTO
{
[MyValidationAttribute]
public string Foo { get; set; }
}
我收到错误消息
没有给出与所需形式相对应的参数 的参数“ myOptionsMonitor” 'MyValidationAttribute.MyValidationAttribute（IOptionsMonitor）'
有没有一种方法可以将依赖项注入用于验证属性？我知道我可以像这样使用ValidationContext
internal class MyValidationAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value,ValidationContext validationContext)
{
if (value != null)
{
IOptionsMonitor<MyOptions> myOptionsMonitor = validationContext.GetService<IOptionsMonitor<MyOptions>>();
// ...
return ValidationResult.Success;
}
return new ValidationResult("Something Failed");
}
}
但是我想使用基类中的FormatErrorMessage方法，但是它无法访问选项服务。
我当前的解决方案
现在，这是我正在使用的代码
[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
internal class CustomValidationAttribute : ValidationAttribute
{
protected override ValidationResult IsValid(object value,ValidationContext validationContext)
{
IOptionsMonitor<MyOptions> myOptionsMonitor = validationContext.GetService<IOptionsMonitor<MyOptions>>();
Dictionary<string,string> myMap = myOptionsMonitor.CurrentValue.MyMap;
string key = value.ToString() ?? string.Empty;
if (myMap.ContainsKey(key))
return ValidationResult.Success;
string[] formattedKeys = myMap.Keys.Select(key => $"'{key}'").ToArray();
string keysText = string.Join(" / ",formattedKeys);
string errorMessage = $"Invalid value. Valid ones are {keysText}";
return new ValidationResult(errorMessage);
}
}
解决方法
属性不是为此目的而设计的。但是您可以改用动作过滤器。
让我们尽可能简化您的属性，我们在那里不需要任何验证逻辑。
[AttributeUsage(AttributeTargets.Property)]
public class CustomValidationAttribute : Attribute
{ }
对于我的示例，我创建了要注入的服务
public class SomeService
{
public bool IsValid(string str)
{
return str == "Valid";
}
}
和我们要验证的类
public class ClassToValidate
{
[CustomValidation]
public string ValidStr { get; set; } = "Valid";
[CustomValidation]
public string InvalidStr { get; set; } = "Invalid";
}
现在，我们终于可以创建动作过滤器来验证我们的属性。在下面的代码段中，我们将在执行控制器动作之前挂入ASP.NET Core管道以执行代码。在这里，我获得了动作参数，并尝试在任何属性上找到CustomValidationAttribute。如果存在，请从属性中获取值，强制转换为类型（我只是调用.ToString()）并传递给您的服务。根据从服务返回的值，我们继续执行或向ModelState字典中添加错误。
public class CustomValidationActionFilter : ActionFilterAttribute
{
private readonly SomeService someService;
public CustomValidationActionFilter(SomeService someService)
{
this.someService = someService;
}
public override void OnActionExecuting(ActionExecutingContext context)
{
var actionArguments = context.ActionArguments;
foreach (var actionArgument in actionArguments)
{
var propertiesWithAttributes = actionArgument.Value
.GetType()
.GetProperties()
.Where(x => x.GetCustomAttributes(true).Any(y => y.GetType() == typeof(CustomValidationAttribute)))
.ToList();
foreach (var property in propertiesWithAttributes)
{
var value = property.GetValue(actionArgument.Value).ToString();
if (someService.IsValid(value))
continue;
else
context.ModelState.AddModelError(property.Name,"ModelState is invalid!!!");
}
}
base.OnActionExecuting(context);
}
}
别忘了将过滤器添加到Startup.cs的管道中！
services.AddMvc(x =>
{
x.Filters.Add(typeof(CustomValidationActionFilter));
});
更新：
如果严格要在属性内部使用依赖项注入，则可以使用服务定位器反模式。为此，我们需要从ASP.NET MVC仿真DependencyResolver.Current
public class CustomValidationAttribute : ValidationAttribute
{
private IServiceProvider serviceProvider;
public CustomValidationAttribute()
{
serviceProvider = AppDependencyResolver.Current.GetService<IServiceProvider>();
}
public override bool IsValid(object value)
{
// scope is required for scoped services
using (var scope = serviceProvider.CreateScope())
{
var service = scope.ServiceProvider.GetService<SomeService>();
return base.IsValid(value);
}
}
}
public class AppDependencyResolver
{
private static AppDependencyResolver _resolver;
public static AppDependencyResolver Current
{
get
{
if (_resolver == null)
throw new Exception("AppDependencyResolver not initialized. You should initialize it in Startup class");
return _resolver;
}
}
public static void Init(IServiceProvider services)
{
_resolver = new AppDependencyResolver(services);
}
private readonly IServiceProvider _serviceProvider;
public object GetService(Type serviceType)
{
return _serviceProvider.GetService(serviceType);
}
public T GetService<T>()
{
return (T)_serviceProvider.GetService(typeof(T));
}
private AppDependencyResolver(IServiceProvider serviceProvider)
{
_serviceProvider = serviceProvider;
}
}
应该在Startup.cs
public void Configure(IApplicationBuilder app,IWebHostEnvironment env)
{
AppDependencyResolver.Init(app.ApplicationServices);
// other code
}