Foolproof Provides Contingent Data Annotation Validation for ASP.NET MVC 2

Published on Author nickriggs21 Comments

I like performing validation using Data Annotations in ASP.NET MVC. However, with complex scenarios, I find myself having to choose a different path. One complex scenario is “contingent scenario” also called “dependent scenario”:

Check out this simple class to demonstrate a contingent validation problem.

private class Person
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public bool Married { get; set; }
    public string MaidenName { get; set; }

Let’s say our validation rule is: “If the user selects Married=true, then the user must also provide a MaidenName”.

Data Annotations, currently, don’t handle validating this rule.  And, I can’t make a custom class-level annotation because that will only validate the model and not the individual item.

What I would like to write is:

public bool Married { get; set; }

public string MaidenName { get; set; }

This simple yet unsupported markup fueled a couple of late night hack-a-thons.   Now, I am pleased to announce the fruits of my labor… my first opensource project: “MVC Foolproof Validation

MVC Foolproof Validation extends the Data Annotation validation provided in ASP.NET MVC. Initial efforts are focused on contingent validation.

Some examples of what is possible:

public class SignUpViewModel
    public string Password { get; set; }

    [EqualTo("Password", ErrorMessage="Passwords do not match.")]
    public string RetypePassword { get; set; }
public class EventViewModel
    public string Name { get; set; }

    public DateTime Start { get; set; }

    public DateTime End { get; set; }

Status of the project:
It’s in development, but it works.
Client validation is supported, both standard MVC and jQuery flavors.

Download the source, take a look and make suggestions. I feel strongly that Foolproof is something the community could really use. I hope to roll out a first release in a couple of weeks.

21 Responses to Foolproof Provides Contingent Data Annotation Validation for ASP.NET MVC 2

  1. Maybe I’m missing something, but I can’t get this to work. I added the .dll file to the lib project in my solution, created a reference to it and still can’t get my class to recognize the attribute names listed.

  2. Hi,
    Can I use foolproof in non MVC projects? (using buddy classes). When I try to use a foolproof attribute and try validation using Validator.TryValidateObject method, it results in a method or operation not implemented exception – from ModelAwareValidationAttribute class.

  3. @Akmal, that doesn’t surprise me. The MVC framework is using the FoolproofValidator class to call a different IsValid() method than what’s in a standard ValidationAttribute.

    So the short answer is No, it can’t run outside of Foolproof.

    The long answer is yes – or probably rather. You would need to create a sub class of Validator that knows to call ModelAwareValidationAttribute’s IsValid(object, object) method.

  4. Very cool. Had to recompile in .NET 4.0 to use in my project. I was wondering if using this still makes sense in 4.0/MVC 3? or would you think the need for the Foolproof library is being replaced by standard MVC enhancement?

  5. One of the project my mate Mic working on is, requires multi-languages for the site. The project is built in mvc3 and we are trying to use data annotations for form elements display-names and validations.

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  8. Hi Nick,

    I would like to work on MVC Foolproof Validation project. I see that it’s a great project and it’s not active from a long time. I would also like to move the project from Codeplex to Github.

    What are your thoughts on this?


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