FluentValidation 11.6.0自定义验证器：服务注入与动态占位符提示

现有Customer类包含以下属性：

public string RegistrationNr 
public bool Archived

已实现AddCustomerValidator验证器且运行正常：

internal sealed class AddCustomerValidator : AbstractValidator<AddCustomerViewModel> 
{ 
    private readonly ICustomerService _customerService; 
    public AddCustomerValidator(ICustomerService customerService) 
    { 
        _customerService = customerService;

        RuleFor(c => c.RegistrationNumber)
            .Must((registrationNumber) =>
            {
                var customer = _customerService.FindByRegistrationNumber(registrationNumber);
                return customer == null;
            })
            .WithMessage("Number already in use.");
     }
 }

当前使用FluentValidation 11.6.0，需要根据已存在客户的Archived状态生成更精准的提示消息："Number already in use for active customer"或"Number already in use for archived customer"。尝试编写自定义静态验证器类时，无法识别_customerService，需解决服务传递/注入的问题。

方法一：直接修改原有验证器（推荐） #

无需额外编写静态类，利用Must的重载获取验证上下文，直接将客户状态注入消息格式化器：

internal sealed class AddCustomerValidator : AbstractValidator<AddCustomerViewModel> 
{ 
    private readonly ICustomerService _customerService; 

    public AddCustomerValidator(ICustomerService customerService) 
    { 
        _customerService = customerService;

        RuleFor(c => c.RegistrationNumber)
            .Must((registrationNumber, context) =>
            {
                // 按原有逻辑格式化注册编号
                var formattedRegNr = AfvoerCheckCommon.Formatters.Formatter.FormatRegNr(registrationNumber);
                var customer = _customerService.FindByRegistrationNumber(formattedRegNr);
                
                if (customer == null)
                    return true;

                // 将客户状态添加到消息格式化器参数中
                context.MessageFormatter.AppendArgument("CustomerStatus", customer.Archived ? "archived" : "active");
                return false;
            })
            .WithMessage("Number already in use for {CustomerStatus} customer.");
    }
}

这种方式直接在原有验证器内完成逻辑，避免了静态类的依赖问题，代码更简洁易维护。

方法二：修改自定义静态验证器 #

如果坚持使用静态扩展方法，需将ICustomerService作为参数传入（静态类无法直接依赖注入）：

1. 更新静态验证器类 #

public static class MyCustomValidators
{
    // 添加ICustomerService作为扩展方法的参数
    public static IRuleBuilderOptions<T, string> RegistrationNumberExists<T>(
        this IRuleBuilder<T, string> rulebuilder, 
        ICustomerService customerService)
    {
        return rulebuilder.Must((rootObject, registrationNumber, context) =>
        {
            var formattedRegNr = AfvoerCheckCommon.Formatters.Formatter.FormatRegNr(registrationNumber);
            var customer = customerService.FindByRegistrationNumber(formattedRegNr);
            
            if (customer == null)
                return true;

            context.MessageFormatter.AppendArgument("CustomerStatus", customer.Archived ? "archived" : "active");
            return false;
        })
        .WithMessage("Number already in use for {CustomerStatus} customer.");
    }
}

2. 在验证器中调用扩展方法 #

internal sealed class AddCustomerValidator : AbstractValidator<AddCustomerViewModel> 
{ 
    private readonly ICustomerService _customerService; 

    public AddCustomerValidator(ICustomerService customerService) 
    { 
        _customerService = customerService;

        // 将注入的服务实例传递给扩展方法
        RuleFor(c => c.RegistrationNumber)
            .RegistrationNumberExists(_customerService);
    }
}

内容的提问来源于stack exchange，提问作者Jeroen E