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，它将允许我连接到我的数据库并告诉我（例如）名称是否唯一。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。

目前我的验证码是这样的：

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return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如下：

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

我也成功注册了此服务，我在我的 Blazor 页面中使用了它。

 services.AddTransient<ILandlordData, LandlordData>();

尽管进行了多次尝试和不同的方法，但我无法（更有可能我不知道如何）注入 DbContext，因此我可以使用 LandlordData Class 来检查记录。

但是我的ApplicationDbContext总是空的！

任何人都可以建议访问我的数据库以执行自定义验证的正确方法。

TIA

Answer 1

But my ApplicationDbContext is always null!

可以参考官方文档here。本恩曾说过 ValidationContext.GetService 为空。不支持在 IsValid 方法中注入验证服务。

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

详细演示：

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);
    }
}

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;
    }

}

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();
}

然后您可以使用您自定义的验证属性：

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 });
    }
}

模型设计：

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

将数据库与自定义验证器一起使用

Using a database with Custom Validators

c#

validation

asp.net-core

blazor

blazor-server-side