Using FluentValidation's WithMessage method with a list of named parameters

Question

I am using FluentValidation and I want to format a message with some of the object\'s properties value. The problem is I have very little experience with expressions and delegat

Answer 1

Extension methods based on ErikE's answer.

public static class RuleBuilderOptionsExtensions
{
    public static IRuleBuilderOptions WithMessage(this IRuleBuilderOptions rule, Func func)
        => DefaultValidatorOptions.WithMessage(rule, "{0}", func);
    public static IRuleBuilderOptions WithMessage(this IRuleBuilderOptions rule, Func func)
        => DefaultValidatorOptions.WithMessage(rule, "{0}", func);
}

Usage examples:

RuleFor(_ => _.Name).NotEmpty()
.WithMessage(_ => $"The name {_.Name} is not valid for Id {_.Id}.");

RuleFor(_ => _.Value).GreaterThan(0)
.WithMessage((_, p) => $"The value {p} is not valid for Id {_.Id}.");