Page Validation for Large Forms in MVC

Summary

A recent application I worked on had a large form that consisted of over 10 tabs worth of information – over 100 fields in total. This information came from another source (a tablet), and needed to be fully validated before being processed further. I searched around on the web looking for an example of how to most efficiently do this, and didn’t find one. Sure the standard MVC unobtrusive validation could be used, but I wanted to improve on it, so that:

1. The user would see validation errors when entering the page.
2. They did not have to fill in every single field with a validation error in order to save, because the information may not be known at the time.

One very important angle is that there has to be two types of validation. The type of validation that must always be validated is for example entering a string into a numeric field, or a characters into a date field. For this, I used standard MVC unobtrusive validation and data annotations.

The only problem I can find with my solution is that client side validation has to be turned off. Its a total server side solution at present. I would be interested in receiving any feedback particularly in this regard as obviously client side validation is a good thing. For me in the app I was working on however, which is an intranet app with a couple of users, turning off client side validation is not a big deal. It might be if the system had hundreds of users.

How it Works

The core MVC validation was used to validate things like data types, required fields, max lengths, in fact anything that if not validated would cause an error when trying to save. I also looked at IValidatableObject. The problem I had was that the validation would do two passes through, it would look at things like Required fields and MaxLengths, then if everything checked out ok would then run the Validate() method on IValidatableObject as well as. I wanted to split this out so I had two tiers of validation – validation that would just come up on screen and not stop the save, and validation that stopped the save.

Getting Started

To start on a tangent, getting all those fields on one page was easy enough – as I was using Bootstrap 3 framework, Bootstrap tabs was a reasonably obvious solution.

I created the model classes, and put the necessary data annotations on these classes to prevent problems with the save, e.g. Max lengths, data types, and required just for fields that were defined as NOT NULL in the database.

The Second Level of Validation

I wanted to use as much of the MVC framework as possible, so the next step was to create an interface, which I called IBcValidatableObject, with one method:

    public interface IBcValidatableObject
    {
        IEnumerable DoValidate(ValidationContext validationContext);
    }

The implementation of this interface in the model is exactly the same as for IValidatableObject, its just that it has to be manually called, it isn’t called automatically by MVC. An example follows:

     public IEnumerable DoValidate(ValidationContext validationContext) {
       var results = new List();

       if (string.IsNullOrWhiteSpace(AssessorName))
       {
           results.Add(new ValidationResult("Assessor Name is mandatory", new [] { "AssessorName" }));
       }

       return results;
     }

The next step is to alter the controller to do the validation when entering the edit page. In this circumstance, ALL the validation needs to be executed, so all errors are displayed on the page:

     // GET: Forms/Edit/5
     public ActionResult Edit(int? id)
     {
         /* Standard MVC processing */
         if (id == null)
         {
             return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
         }

         var form = _service.GetEnrolFormById((int)id);
         if (form == null)
         {
             return HttpNotFound();
         }

         /* Perform Full validation of ALL fields */
         var errors = _service.FullValidation(enrolForm);

         /* Add any errors to the ModelState */
         AddErrorsToModelState(errors);

         /* Populate Drop down lists for the form (not shown) */
         DoDropDownLists();

         return View(form);
     }

AddErrorsToModelState was a function I created to translate the output from the validate method to the page, as follows:

     private void AddErrorsToModelState(IEnumerable errors)
     {
         foreach (var error in errors)
         {
             if (!error.MemberNames.Any())
             {
                 ModelState.AddModelError(string.Empty, error.ErrorMessage);
             }
             else
             {
                 foreach (var member in error.MemberNames)
                 {
                     ModelState.AddModelError(member, error.ErrorMessage);
                 }
             }
         }
     }

When the user pressed Save, the standard MVC validation has to take place to ensure the record can be saved, then additional validation takes place to ensure that the correct errors are displayed on the page:

     // POST: Forms/Edit/5
     [HttpPost]
     [ValidateAntiForgeryToken]
     public ActionResult Edit(int id)
     {
         /* Get the data from the service */
         var form = _service.GetEnrolFormById(id);

         /* Try to get the data from the model and update, if successful, save is ok to do */
         if (TryUpdateModel(form))
         {
             form.Id= id;
             _service.Save(form);
         }

         /* Get additional errors for display purposes, if there aren't any I'm returning */
         /* to the previous page, if there are, I'm displaying them */
         var errors = _service.AdditionalValidation(form).ToList();
         if (!errors.Any())
             return RedirectToAction("Index");

         AddErrorsToModelState(errors);
     
         DoEnrolFormDropDownLists();

         return View(enrolForm);
     }

Thats it! The only thing missing from this example is the code I used in the service to do the different validation I needed:

1. Full Validation
2. Additional Validation

Full Validation

     public IEnumerable FullValidation(Form form)
     {
         var validationResults = new List();
         validationResults.AddRange(ObjectValidation(form.Data).ToList());
         validationResults.AddRange(AdditionalValidation(enrolForm));
         return validationResults;
     }

     /* ObjectValidation calls the standard validation */
     private IEnumerable ObjectValidation(object data)
     {
         var context = new ValidationContext(data, serviceProvider: null, items: null);
         var results = new List();
         Validator.TryValidateObject(data, context, results);
         return results;
     }  

Additional Validation

     public IEnumerable AdditionalValidation(Form form)
     {
         var validationResults = new List();
         var bcObject = form.Data as IBcValidatableObject;
         if (bcObject != null)
         {
             var validationContext = new ValidationContext(bcObject, serviceProvider: null, items: null);
             validationResults.AddRange(bcObject.DoValidate(validationContext));
         }

         return validationResults;
     }

N.B. In this example for clarity, I have removed the code that handles multiple sections in my model.

As always, any and all feedback welcome.

About Phil

I have been working as a software developer since 1983. This blog could have been called "From Fortran 77, C and Cobol to C# in 20 (not so) easy years", but it doesn't sound quite right somehow. Besides I'm talking about what's happened since 2003, not before!