Custom Validation Attribute error message not showing with ValidationMessageFor

Question

I have this custom validation :

[AttributeUsage(AttributeTargets.Property)]
public class CollectionNotEmptyAttribute : ValidationAttribute
{
    private const string errorMessage = "'{0}' must have at least one element.";

    public CollectionNotEmptyAttribute()
        : base(errorMessage)
    { 

    }

    public override bool IsValid(object value)
    {
        var collection = value as ICollection;
        if (collection != null)
        {
            return collection.Count > 0;
        }

        return false;
    }

    public override string FormatErrorMessage(string name)
    {
        return String.Format(this.ErrorMessageString, name);
    }
}

My viewmodel

public class ProjectViewModel
{
    public ProjectViewModel()
    {
        this.Users = new Collection<UserProjectViewModel>();
    }

    public int ProjectID { get; set; }
    [CollectionNotEmpty]
    public Collection<UserProjectViewModel> Users { get; set; }
}

My View

@Html.ValidationMessageFor(m => m.Users)

The validation is working fine, Model.IsValid returning false if collection count below 1, but the error message is not showing.

Any help will be appreciated.

kamil-mrzyglod · Accepted Answer · 2015-07-15 08:55:16Z

3

I believe you should override other IsValid method:

protected virtual ValidationResult IsValid(
   Object value,
   ValidationContext validationContext
)

since it allows you to return ValidationResult with proper error message.

The one you overrode just determines whether result is valid or not.

answered Jul 15, 2015 at 8:55

kamil-mrzyglod

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