DRY Validation with MVC2

Question

Hi All,

I'm trying to figure out how I can define validation rules for my domain objects in one single location within my application but have run in to a snag...

Some background: My application has several parts: - Database - DAL - Business Logic Layer - SOAP API Layer - MVC website

The MVC website accesses the database via the SOAP API, just as third parties would. We are using server and and client side validation on the MVC website as well as in the SOAP API Layer.

To avoid having to manually write client side validation we are implementing strongly typed views in conjunction with the Html.TextBoxFor and Html.ValidationMessageFor HTML helpers, as shown in Step 3 here. We also create custom models for each form where one form takes input for multiple domain objects.

This is where the problem begins, the HTML helpers read from the model for the data annotation validation attributes. In most cases our forms deal with multiple domain objects and you can't specify more than one type in the <%@Page ... Inherits="System.Web.Mvc.ViewPage<MvcApplication.Models.SomeModel>" %> page directive. So we are forced to create a custom model class, which would mean duplicating validation attributes from the domain objects on to the model class.

I've spent quite some time looking for workarounds to this, such has referencing the same MetadataType from both the domain class and the custom MVC models, but that won't work for several reasons:

1. You can only specify one MetadataType attribute per class, so its a problem if a model references multiple domain objects, each with their own metadata type.

2. The data annotation validation code throws an exception if the model class doesn't contain a property that is specified in the referenced MetadataType which is a problem with the model only deals with a subset of the properties for a given domain object.

I've looked at other solutions as well but to no avail. If anyone has any ideas on how to achieve a single source for validation logic that would work across MVC client and server side validation functionality and other locations (such as my SOAP API) I would love to hear it!

Thanks in advance,

Matthew

Answer 1

How about returning a container class that has nested types in your action method?

http://weblogs.asp.net/blogs/rajbk/image_63B7D5D4.png

Answer 2

What you should do is instead of trying to replicate the structure in the view models, use your existing models in the data model classes. When you bind the form data back to the view model, you can restrict which columns will be bound back using the [Bind] attribute on the parameter. Or use any other approaches to do this.

So if your model creates classes like Product User and Category, and your view model needs to use some of their properties, create a view model like this:

public class PageViewModel
{
    public Product Product { get; set; }
    public Category Category { get; set; }
    public User User { get; set; }
}

In your page you will be able to use them with

<%: Html.EditorFor(m => m.Product.ProductName) %>

In this case the validation attributes from your actual classes will be used, as required.
Does that give you an acceptable solution?