将数据库与自定义验证器一起使用

Question

我希望能够创建一个自定义验证器，这将允许我连接到我的数据库并告诉我（例如）一个名称是否是唯一的。我曾经在 EF 中使用 [Remote] 属性，但我了解到您不能将其与 Blazor 一起使用。

我目前的验证码是这样的：

public class LandlordNameIsUniqueValidator : ValidationAttribute 
{  
     protected override ValidationResult IsValid(object value, ValidationContext validationContext)
     {  
            //This is always null
            var context = (ApplicationDbContext)validationContext.GetService(typeof(ApplicationDbContext));          
            var checkName = new LandlordData(context);

            var name = value.ToString();
            var nameExists = checkName.CheckNameIsUnique(name);

            if (!exists)
            {
                return null;
            }

            return new ValidationResult(ErrorMessage, new[] { validationContext.MemberName });
        }
    }

我使用的代码（在应用程序的其他部分成功）如下，这将返回一个布尔值：

public class LandlordData : ILandlordData
{
   private readonly ApplicationDbContext _context; 
   public LandlordData(ApplicationDbContext context)
   {
       _context = context;
   }
   
   public bool CheckNameIsUnique(string name)
   {
      var exists = _context.Landlords
         .AsNoTracking()
         .Any(x => x.LandlordName == name);
      return exists;
   }
}

在StartUp.cs中如下：

 services.AddDbContext<ApplicationDbContext>(options =>
               options.UseSqlServer(
                   _config.GetConnectionString("DefaultConnection")),
                   ServiceLifetime.Transient);

我还成功注册了此服务，并在我的 Blazor 页面中使用它。

 services.AddTransient<ILandlordData, LandlordData>();

尽管多次尝试和不同的方法，我不能（更可能我不知道如何）注入DbContext，所以我可以使用LandlordData Class 来检查记录。

但我的ApplicationDbContext 始终为空！

谁能建议正确的方法来访问我的数据库以执行自定义验证。

TIA

Answer 1

但我的 ApplicationDbContext 始终为空！

可以参考官方文档here。 benn 说ValidationContext.GetService 为空。不支持在IsValid 方法中注入服务进行验证。

对于您的场景，您需要先阅读answer 以了解如何将IServiceProvider 传递给ValidationContext。

详细演示：

1. 自定义DataAnnotationsValidator

   public class DIDataAnnotationsValidator: DataAnnotationsValidator
   {
       [CascadingParameter] EditContext DICurrentEditContext { get; set; }
   
       [Inject]
       protected IServiceProvider ServiceProvider { get; set; }
       protected override void OnInitialized()
       {
           if (DICurrentEditContext == null)
           {
               throw new InvalidOperationException($"{nameof(DataAnnotationsValidator)} requires a cascading " +
                   $"parameter of type {nameof(EditContext)}. For example, you can use {nameof(DataAnnotationsValidator)} " +
                   $"inside an EditForm.");
           }
   
           DICurrentEditContext.AddDataAnnotationsValidationWithDI(ServiceProvider);
       }
   }
   

2. 自定义EditContextDataAnnotationsExtensions

   public static class EditContextDataAnnotationsExtensions
   {
       private static ConcurrentDictionary<(Type ModelType, string FieldName), PropertyInfo> _propertyInfoCache
       = new ConcurrentDictionary<(Type, string), PropertyInfo>();
   
       public static EditContext AddDataAnnotationsValidationWithDI(this EditContext editContext, IServiceProvider serviceProvider)
       {
           if (editContext == null)
           {
               throw new ArgumentNullException(nameof(editContext));
           }
   
           var messages = new ValidationMessageStore(editContext);
   
           // Perform object-level validation on request
           editContext.OnValidationRequested +=
               (sender, eventArgs) => ValidateModel((EditContext)sender, serviceProvider, messages);
   
           // Perform per-field validation on each field edit
           editContext.OnFieldChanged +=
               (sender, eventArgs) => ValidateField(editContext, serviceProvider, messages, eventArgs.FieldIdentifier);
   
           return editContext;
       }
       private static void ValidateModel(EditContext editContext, IServiceProvider serviceProvider,ValidationMessageStore messages)
       {
           var validationContext = new ValidationContext(editContext.Model, serviceProvider, null);
           var validationResults = new List<ValidationResult>();
           Validator.TryValidateObject(editContext.Model, validationContext, validationResults, true);
   
           // Transfer results to the ValidationMessageStore
           messages.Clear();
           foreach (var validationResult in validationResults)
           {
               foreach (var memberName in validationResult.MemberNames)
               {
                   messages.Add(editContext.Field(memberName), validationResult.ErrorMessage);
               }
           }
   
           editContext.NotifyValidationStateChanged();
       }
   
       private static void ValidateField(EditContext editContext, IServiceProvider serviceProvider, ValidationMessageStore messages, in FieldIdentifier fieldIdentifier)
       {
           if (TryGetValidatableProperty(fieldIdentifier, out var propertyInfo))
           {
               var propertyValue = propertyInfo.GetValue(fieldIdentifier.Model);
               var validationContext = new ValidationContext(fieldIdentifier.Model, serviceProvider, null)
               {
                   MemberName = propertyInfo.Name
               };
               var results = new List<ValidationResult>();
   
               Validator.TryValidateProperty(propertyValue, validationContext, results);
               messages.Clear(fieldIdentifier);
               messages.Add(fieldIdentifier, results.Select(result => result.ErrorMessage));
   
               // We have to notify even if there were no messages before and are still no messages now,
               // because the "state" that changed might be the completion of some async validation task
               editContext.NotifyValidationStateChanged();
           }
       }
   
       private static bool TryGetValidatableProperty(in FieldIdentifier fieldIdentifier, out PropertyInfo propertyInfo)
       {
           var cacheKey = (ModelType: fieldIdentifier.Model.GetType(), fieldIdentifier.FieldName);
           if (!_propertyInfoCache.TryGetValue(cacheKey, out propertyInfo))
           {
               // DataAnnotations only validates public properties, so that's all we'll look for
               // If we can't find it, cache 'null' so we don't have to try again next time
               propertyInfo = cacheKey.ModelType.GetProperty(cacheKey.FieldName);
   
               // No need to lock, because it doesn't matter if we write the same value twice
               _propertyInfoCache[cacheKey] = propertyInfo;
           }
   
           return propertyInfo != null;
       }
   
   }
   

3. 将DataAnnotationsValidator 替换为DIDataAnnotationsValidator

   <EditForm Model="@book" >
       <DIDataAnnotationsValidator />   //change here
       <ValidationSummary />
       <div class="row content">
           <div class="col-md-2"><label for="Name">Name</label></div>
           <div class="col-md-3"><InputText id="name" @bind-Value="book.UserName" /></div>
           <ValidationMessage For=" (() => book.UserName)" />
   
       </div>  
       <div class="row content">
           <button type="submit">Submit</button>
       </div>
   </EditForm>
   
   @code {
       Booking book= new Booking();
   }
   

4. 然后你可以使用你自定义的验证属性：

   public class LandlordNameIsUniqueValidator : ValidationAttribute
   {
       protected override ValidationResult IsValid(object value, ValidationContext validationContext)
       {
           //This is always null
           var context = (LykosqlContext)validationContext.GetService(typeof(LykosqlContext));
           var checkName = new LandlordData(context);
   
           var name = value.ToString();
           var nameExists = checkName.CheckNameIsUnique(name);
   
   
           return new ValidationResult(ErrorMessage, new[] { validationContext.MemberName });
       }
   }
   

5. 模型设计：

   public class Booking
   {
       public int Id { get; set; }
       [LandlordNameIsUniqueValidator]
       public string UserName { get; set; }
   }