如何在不破坏DI注册的情况下向FluentValidation验证器传参？

需要通过.SetValidator()方法从父验证器向子验证器传递参数，但子验证器带有参数时，使用FluentValidation的自动注册功能将其注册到DI容器时遇到构造错误。

父验证器代码 #

public class FooValidator: AbstractValidator<Foo>
{
    public FooValidator()
    {
        RuleFor(foo => foo.Bar)
            .SetValidator(foo => new BarValidator(foo.SomeStringValue))
            .When(foo => foo.Bar != null);
    }
}

子验证器代码 #

public class BarValidator: AbstractValidator<Bar>
{
    public BarValidator(string someStringValue)
    {
        RuleFor(bar => bar.Baz)
            .Must(BeValid(bar.Baz, someStringValue)
            .When(bar => bar.Baz != null);
    }
    
    private static bool BeValid(Baz baz, string someStringValue)
    {
        return baz == someStringValue; 
    }
}

DI注册代码 #

services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly(), ServiceLifetime.Transient);

错误信息 #

System.AggregateException: Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: FluentValidation.IValidator`1[Domain.ValueObjects.Bar] Lifetime: Transient ImplementationType: Application.Common.Validators.BarValidator': 
    Unable to resolve service for type 'System.String' while attempting to activate 'Application.Common.Validators.BarValidator'.)

---> System.InvalidOperationException: Unable to resolve service for type 'System.String' while attempting to activate 'Application.Common.Validators.BarValidator'.
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType, CallSiteChain callSiteChain)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, Int32 slot)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.GetCallSite(ServiceDescriptor serviceDescriptor, CallSiteChain callSiteChain)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.ValidateService(ServiceDescriptor descriptor)
   --- End of inner exception stack trace ---
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.ValidateService(ServiceDescriptor descriptor)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider..ctor(ICollection`1 serviceDescriptors, ServiceProviderOptions options)
   --- End of inner exception stack trace ---
   at Microsoft.Extensions.DependencyInjection.ServiceProvider..ctor(ICollection`1 serviceDescriptors, ServiceProviderOptions options)
   at Microsoft.Extensions.DependencyInjection.ServiceCollectionContainerBuilderExtensions.BuildServiceProvider(IServiceCollection services, ServiceProviderOptions options)
   at Microsoft.Extensions.Hosting.HostApplicationBuilder.Build()
   at Microsoft.AspNetCore.Builder.WebApplicationBuilder.Build()
   at Program.<Main>$(String[] args) in C:\Program.cs:line 9

环境信息 #

• .NET 7
• FluentValidation v11.2.2
• Microsoft.Extensions.DependencyInjection

已尝试的无效方法 #

_ = services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly(), ServiceLifetime.Transient, filter => filter.ValidatorType != typeof(BarValidator));
_ = services.AddTransient<IValidator<Bar>>(_ => new BarValidator(""));

解决方案 #

1. 修正子验证器的语法错误 #

子验证器中Must方法的调用存在语法错误，需改为Lambda表达式传递参数：

public class BarValidator: AbstractValidator<Bar>
{
    public BarValidator(string someStringValue)
    {
        RuleFor(bar => bar.Baz)
            .Must(baz => BeValid(baz, someStringValue)) // 修正为Lambda表达式
            .When(bar => bar.Baz != null);
    }
    
    private static bool BeValid(Baz baz, string someStringValue)
    {
        // 增加空判断，避免空引用异常
        return baz?.ToString() == someStringValue; 
    }
}

2. 排除子验证器的自动注册 #

由于父验证器是手动实例化子验证器，不需要DI容器提供BarValidator的实例，因此需要阻止FluentValidation自动注册它，有两种方式：

方式一：使用过滤条件排除

在自动注册时通过filter排除BarValidator，且不需要手动注册它：

services.AddValidatorsFromAssembly(
    Assembly.GetExecutingAssembly(),
    ServiceLifetime.Transient,
    // 确保这里的类型是正确的BarValidator类型（注意命名空间）
    filter => filter.ValidatorType != typeof(BarValidator)
);

方式二：使用[ValidatorIgnore]特性

给BarValidator添加FluentValidation提供的[ValidatorIgnore]特性，自动注册时会忽略该验证器：

using FluentValidation;

[ValidatorIgnore]
public class BarValidator: AbstractValidator<Bar>
{
    // 代码不变
}

此时DI注册代码可简化为：

services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly(), ServiceLifetime.Transient);

关键说明 #

错误的核心原因是AddValidatorsFromAssembly会自动扫描并注册所有继承AbstractValidator<T>的类型，但BarValidator的构造函数需要字符串参数，DI容器无法自动解析该参数。而父验证器中是直接手动创建BarValidator实例，完全不需要DI容器介入，因此只需阻止BarValidator被注册到DI即可解决问题。

内容的提问来源于stack exchange，提问作者trymv