Advice with Dynamic Forms in ASP.NET MVC

Question

I am working on rendering a dynamic form in an ASP.NET MVC view that will meet these requirements:

• Fields can be validated
• State is preserved when the for

Answer 1

Although not an expert I had to create a solution where my main object had a list of values. Lets call it Object A has a list of ApplicationValues that are mapped in the database. The ApplicationValues have a Key (the form field e.g. PhoneNumber) and the Value.

As the ApplicationValues were an EntitySet I had to create get and set methods to correctly handle setting a specific ApplicationValue. I also had a list of ApplicationRules in my database that defined what these application values could take.

Here is a snippet of code that may help you develop a solution for your needs.

public partial ApplicationValue
{
    public string Key;
    public string Value;
}

public partial ApplicationRule
{
    public string ValidationFormat;
    public string ValidationError;
    public bool Required;
}

public partial class A
{
    public void SetValue(string key, string value)
    {
        //ApplicationValues is the list of values associated to object A
        ApplicationValue v = ApplicationValues.SingleOrDefault
        (k => k.Key == key);

        //if we already have this value
        if (v != null)
        {   //...then we can simply set and return
            v.Value = value;
            return;
        }

        //else we need to create a new ApplicationValue
        v = new ApplicationValue
            {
                AffinityID = this.ID,
                Key = key,
                Value = value
            };

        ApplicationValues.Add(v);
    }

    public string GetValue(ApplicationField key)
    {
        return GetValue(key, String.Empty);
    }

    public string GetValue(ApplicationField key, string defaultValue)
    {
        if (ApplicationValues == null)
            return defaultValue;

        ApplicationValue value = ApplicationValues.SingleOrDefault
        (f => f.Key == key.ToString());

        return (value != null) ? value.Value : defaultValue;
    }

And then to do the form validation I loop through ApplicationRules (which defines if a field is required, contains a regex etc) and match it to the FormCollection.

public ActionResult Details(FormCollection form)
{
    IList applicationRules = //get my rules from the DB

    if (!(ValidateApplication(applicationRules, form, a)))
    {
        ModelState.AddModelError("message", "Please review the errors below.");
        return View(a);
    }
    ...
}

private bool ValidateApplication(IList applicationRules,
                                 FormCollection form, A a)
    {
        //loop through the application rules
        foreach (ApplicationRule ar in applicationRules)
        {
            //try and retrieve the specific form field value using the key
            string value = form[ar.Key];

            if (value == null)
                continue;

            //set the model value just in case there is an error
            //so we can show error messages on our form
            ModelState.SetModelValue(ar.Key, ValueProvider[ar.Key]);

            //if this rule is required
            if (ar.Required)
            {   //...then check if the field has a value
                if (String.IsNullOrEmpty(value))
                {
                    ModelState.AddModelError(ar.Key, "Field is required");
                    continue;
                }
            }

            //if this rule has a validation format
            if (!String.IsNullOrEmpty(ar.ValidationFormat))
            {   //...then check the value is of the correct format
                Regex re = new Regex(ar.ValidationFormat);

                if (!re.IsMatch(value))
                {
                    ModelState.AddModelError(ar.Key, ar.ValidationError);
                    continue;
                }
            }

            a.SetValue(ar.Key, value);
        }

        return ModelState.IsValid;
    }