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

.net, c#, fluentvalidation, func, linq

Solution

You can't do that with the WithMessage in FluentValidation but you can high-jack the CustomState property and inject your message there. Here is a working example; Your other option is to fork FluentValidation and make an additional overload for the WithMethod.

This is a console application with references to FluentValidation from Nuget and the JamesFormater from this blog post:

http://haacked.com/archive/2009/01/04/fun-with-named-formats-string-parsing-and-edge-cases.aspx

The Best answer. Took inspiration from Ilya and realized you can just piggyback off the extension method nature of fluent validation. So The below works with no need to modify anything in the library.

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.UI;
using FluentValidation;

namespace stackoverflow.fv
{
    class Program
    {
        static void Main(string[] args)
        {
            var target = new My() { Id = "1", Name = "" };
            var validator = new MyValidator();
            var result = validator.Validate(target);

            foreach (var error in result.Errors)
                Console.WriteLine(error.ErrorMessage);

            Console.ReadLine();
        }
    }

    public class MyValidator : AbstractValidator<My>
    {
        public MyValidator()
        {
            RuleFor(x => x.Name).NotEmpty().WithNamedMessage("The name {Name} is not valid for Id {Id}");
        }
    }

    public static class NamedMessageExtensions
    {
        public static IRuleBuilderOptions<T, TProperty> WithNamedMessage<T, TProperty>(
            this IRuleBuilderOptions<T, TProperty> rule, string format)
        {
            return rule.WithMessage("{0}", x => format.JamesFormat(x));
        }
    }

    public class My
    {
        public string Id { get; set; }
        public string Name { get; set; }
    }

    public static class JamesFormatter
    {
        public static string JamesFormat(this string format, object source)
        {
            return FormatWith(format, null, source);
        }

        public static string FormatWith(this string format
            , IFormatProvider provider, object source)
        {
            if (format == null)
                throw new ArgumentNullException("format");

            List<object> values = new List<object>();
            string rewrittenFormat = Regex.Replace(format,
              @"(?<start>\{)+(?<property>[\w\.\[\]]+)(?<format>:[^}]+)?(?<end>\})+",
              delegate(Match m)
              {
                  Group startGroup = m.Groups["start"];
                  Group propertyGroup = m.Groups["property"];
                  Group formatGroup = m.Groups["format"];
                  Group endGroup = m.Groups["end"];

                  values.Add((propertyGroup.Value == "0")
                    ? source
                    : Eval(source, propertyGroup.Value));

                  int openings = startGroup.Captures.Count;
                  int closings = endGroup.Captures.Count;

                  return openings > closings || openings % 2 == 0
                     ? m.Value
                     : new string('{', openings) + (values.Count - 1)
                       + formatGroup.Value
                       + new string('}', closings);
              },
              RegexOptions.Compiled
              | RegexOptions.CultureInvariant
              | RegexOptions.IgnoreCase);

            return string.Format(provider, rewrittenFormat, values.ToArray());
        }

        private static object Eval(object source, string expression)
        {
            try
            {
                return DataBinder.Eval(source, expression);
            }
            catch (HttpException e)
            {
                throw new FormatException(null, e);
            }
        }
    }
}

Problem

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 delegates in C#. FluentValidation already provides a way to do this with format arguments. ``` RuleFor(x => x.Name).NotEmpty() .WithMessage("The name {1} is not valid for Id {0}", x => x.Id, x => x.Name); ``` I would like to do something like this to avoid having to change the message string if I change the order of the parameters. ``` RuleFor(x => x.Name).NotEmpty() .WithMessage("The name {Name} is not valid for Id {Id}", x => new { Id = x.Id, Name = x.Name }); ``` The original method signature looks like this: ``` public static IRuleBuilderOptions<T, TProperty> WithMessage<T, TProperty>( this IRuleBuilderOptions<T, TProperty> rule, string errorMessage, params Func<T, object>[] funcs) ``` I was thinking of providing this method with a list of Func. Anyone can help me with this?

Original source

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