ASP.NET Core Web API - 'IRuleBuilderInitial<CustomerTransactionRequestDto, decimal>' does not contain a definition for 'CustomCurrency'

Question

Validation is done in ASP.NET Core-6 Web API using Fluent Validation. So, I have this code:

Custom Validator:

public static IRuleBuilder<T, string> CustomCurrency<T>(this IRuleBuilder<T, string> ruleBuilder)
{
    var options = ruleBuilder
        .Matches(@"^\d+.\d{1,2}$")
        .WithMessage("Appropriate Currency format should be xxxxxxxxxxx.xx");

    return options;
}

DTO:

public class CustomerTransactionRequestDto
{
    public decimal Amount { get; set; }
}

Then the validator:

public class CustomerTransactionRequestValidator : AbstractValidator<CustomerTransactionRequestDto>
{
    public CustomerTransactionRequestValidator()
    {
        RuleFor(p => p.Amount).CustomCurrency()
            .NotEmpty().WithMessage("Amount should be not empty. ERROR!");
    }
}

The problem is that I got this error:

Error CS1929 'IRuleBuilderInitial<CustomerTransactionRequestDto, decimal>' does not contain a definition for 'CustomCurrency' and the best extension method overload 'AuthValidatorSettings.CustomCurrency(IRuleBuilder<CustomerTransactionRequestDto, string>)' requires a receiver of type 'IRuleBuilder<CustomerTransactionRequestDto, string>'

Then it highlights:

RuleFor(p => p.Amount)

How do I get this sorted out?

Thank you

Answer 1

The error message hints that types don't match. You have a custom validator based on IRuleBuilder<T, string> while you are trying to chain it to IRuleBuilderInitial<CustomerTransactionRequestDto, decimal>. You have a custom validator based on string property, while on the other end a decimal property.

To fix this, change the type of Amount property from decimal to string:

public class CustomerTransactionRequestDto
{
    public string Amount { get; set; }
}

That way, you can use the validators you already defined in CustomCurrency() like Matches() which are available for string properties.

If decimal property is not a mistake, then I'd suggest adding support for decimal in CustomCurrency() custom validator, like this:

public static IRuleBuilder<T, decimal> CustomCurrency<T>(this IRuleBuilder<T, decimal> ruleBuilder)
{
    // TODO: Your validation.
}