How to handle Booleans/CheckBoxes in ASP.NET MVC 2 with DataAnnotations?

Question

I\'ve got a view model like this:

public class SignUpViewModel
{
    [Required(ErrorMessage = \"Bitte lesen und akzeptieren Sie die AGB.\")]
    [DisplayName         


        

Answer 1

My solution is this simple custom attribute for boolean values:

public class BooleanAttribute : ValidationAttribute
{
    public bool Value
    {
        get;
        set;
    }

    public override bool IsValid(object value)
    {
        return value != null && value is bool && (bool)value == Value;
    }
}

Then you can use it like this in your model:

[Required]
[Boolean(Value = true, ErrorMessage = "You must accept the terms and conditions")]
[DisplayName("Accept terms and conditions")]
public bool AcceptsTerms { get; set; }

Answer 2

I got it by creating a custom attribute:

public class BooleanRequiredAttribute : RequiredAttribute 
{
    public override bool IsValid(object value)
    {
        return value != null && (bool) value;
    }
}

Answer 3

For people who are having trouble getting this working for validation on the client side (formerly me): make sure you have also

1. Included <% Html.EnableClientValidation(); %> before the form in the view
2. Used <%= Html.ValidationMessage or Html.ValidationMessageFor for the field
3. Created a DataAnnotationsModelValidator which returns a rule with a custom validation type
4. Registered the class deriving from DataAnnotationsModelValidator in the Global.Application_Start

http://www.highoncoding.com/Articles/729_Creating_Custom_Client_Side_Validation_in_ASP_NET_MVC_2_0.aspx

is a good tutorial on doing this, but misses step 4.

Answer 4

[Compare("Remember", ErrorMessage = "You must accept the terms and conditions")]
public bool Remember { get; set; }

Answer 5

I would create a validator for both Server AND Client side. Using MVC and unobtrusive form validation, this can be achieved simply by doing the following:

Firstly, create a class in your project to perform the server side validation like so:

public class EnforceTrueAttribute : ValidationAttribute, IClientValidatable
{
    public override bool IsValid(object value)
    {
        if (value == null) return false;
        if (value.GetType() != typeof(bool)) throw new InvalidOperationException("can only be used on boolean properties.");
        return (bool)value == true;
    }

    public override string FormatErrorMessage(string name)
    {
        return "The " + name + " field must be checked in order to continue.";
    }

    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        yield return new ModelClientValidationRule
        {
            ErrorMessage = String.IsNullOrEmpty(ErrorMessage) ? FormatErrorMessage(metadata.DisplayName) : ErrorMessage,
            ValidationType = "enforcetrue"
        };
    }
}

Following this, annotate the appropriate property in your model:

[EnforceTrue(ErrorMessage=@"Error Message")]
public bool ThisMustBeTrue{ get; set; }

And Finally, enable client side validation by adding the following script to your View:

<script type="text/javascript">
    jQuery.validator.addMethod("enforcetrue", function (value, element, param) {
        return element.checked;
    });
    jQuery.validator.unobtrusive.adapters.addBool("enforcetrue");
</script>

Note: We already created a method GetClientValidationRules which pushes our annotation to the view from our model.

Answer 6

"Required" is the wrong validation, here. You want something akin to "Must have the value true," which is not the same as "Required". What about using something like:

[RegularExpression("^true")]

?