MVC: Override default ValidationMessage

Question

In the world of MVC I have this view model...

public class MyViewModel{

[Required]
public string FirstName{ get; set; }    }

...and this s

Answer 1

using Resources;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Reflection;
using System.Resources;
using System.Web;
using System.Web.Mvc;

public class CustomRequiredAttribute : RequiredAttribute,  IClientValidatable
{
    public CustomRequiredAttribute()
    {
        ErrorMessageResourceType = typeof(ValidationResource);
        ErrorMessageResourceName = "RequiredErrorMessage";
    }


    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {


        yield return new ModelClientValidationRule
        {
            ErrorMessage = GetRequiredMessage(metadata.DisplayName),
            ValidationType = "required"
        };
    }


    private string GetRequiredMessage(string displayName) {

        return displayName + " " + Resources.ValidationResource.RequiredErrorMessageClient;        

    }


}

App_GlobalResources/ValidationResource.resx

Now use data annotation

[CustomRequired]

Answer 2

public class GenericRequired: RequiredAttribute
{
    public GenericRequired()
    {
        this.ErrorMessage = "{0} Blah blah"; 
    }
}

Answer 3

Just change

[Required] 

to

[Required(ErrorMessage = "Your Message, Bla bla bla aaa!")]

Answer 4

You can write your own attribute:

public class MyRequiredAttribute : ValidationAttribute
{
    MyRequiredAttribute() : base(() => "{0} blah blah blah blaaaaaah")
    {

    }

    public override bool IsValid(object value)
    {
        if (value == null)
        {
            return false;
        }
        string str = value as string;
        if (str != null)
        {
            return (str.Trim().Length != 0);
        }
        return true;
    }
}

This is copy of RequiredAttribute from Reflector with changed error message.

Answer 5

This worked for me. Carefully read the comments inside the code. (Based on Chad's answer).

 // Keep the name the same as the original, it helps trigger the original javascript 
 // function for client side validation.

        public class RequiredAttribute : System.ComponentModel.DataAnnotations.RequiredAttribute, IClientValidatable
            {
                public RequiredAttribute()
                {
                    this.ErrorMessage = "Message" // doesnt get called again. only once.
                }

                public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
                {
                    yield return new ModelClientValidationRule
                    {
                        ErrorMessage = "Message", // this gets called on every request, so it's contents can be dynamic.
                        ValidationType = "required"
                    };
                }
            }

Answer 6

It seems that RequiredAttribute doesn't implement IClientValidatable, so if you override the RequiredAttribute it breaks client side validation.

So this is what I did and it works. Hope this helps someone.

public class CustomRequiredAttribute : RequiredAttribute, IClientValidatable
{
    public CustomRequiredAttribute()
    {
        this.ErrorMessage = "whatever your error message is";
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        yield return new ModelClientValidationRule
        {
            ErrorMessage = this.ErrorMessage,
            ValidationType = "required"
        };
    }
}