Question

I’ve been struggling with refactoring how I’m doing Model validations for a while now. My applications are all ASP.NET MVC 2 (.Net 3.5 framework). I’ve read the related questions for this subject and they’re not exactly the same as what I’m asking.

Currently, for page validations, I generally stuck with a hodge-podge of if/else statements. The issue is that sometimes field B is validated if field A is a certain value, but field A has it’s own validations as well. In some cases there are roles that come into play and this may altar the validations as well depending on the role of the user (i.e. don’t validate fields the user with role x can’t modify).

My questions boil down to this:

1) How can I handle validations in an easier to read way? I’ve looked at DataAnnotations and they’re not enough. A data annotation handles validation for a field’s value, where as the validations that may need to be done depend on both the field’s value and the value’s of other properties on the object.

2) How can I integrate a validation framework with ASP.NET MVC 2?

The thing I truly hate about how I’m doing my validations now is that, when I add a model error, I am hard coding the key for that property. That’s pretty bad. Still, I’m not sure how to get the key for said property such that it matches the html field that was created by the html helper.

For example, in my view, I am using an editor template to display the fields for my customer object.

   <%= Html.EditorFor(m => m.CustomerInfo) %>

Part of the html generated creates the field for the FirstName:

<input id="CustomerInfo_FirstName" name="CustomerInfo.FirstName" style="width:330px;" type="text" value="John" />

In order for the framework to still highlight the field with the necessary CSS, I am forcing this validation like so:

//Ignore that this can be done with DataAnnotations. This is just a simple example.   
if (String.IsnullOrEmpty(customerInfo.FirstName) )
{
    ModelState.AddModelError("CustomerInfo.FirstName",
    "First Name is required.");
}

This is what I see as the major issue. I don’t have a good way to know the name of the field on the page. It seems to take the pattern of

 <objectname>.<propertyname>

, but I would really want something more reliable.

To get the object name, I think I could pull it out of the ModelBindingContext class, but I’m not sure how to get an instance of this from inside of the controller. For the property name, I could use somekind of lambda that would return the name of the property as a string.

To summarize, I am looking for: 1) some kind of validation framework that would allow complex validations 2) Some way to identify the key to use in the ModelState.AddModelError method such that MVC’s error styling still works.

Answer 1

You really are looking for FluentValidation

However, I’m not sure if it supports MVC2. It supports for sure MVC3 and MVC4 though.

Example code from its website:

public class CustomerValidator: AbstractValidator<Customer> {
  public CustomerValidator() {
    RuleFor(customer => customer.Surname).NotEmpty();
    RuleFor(customer => customer.Forename).NotEmpty().WithMessage("Please specify a first name");
    RuleFor(customer => customer.Company).NotNull();
    RuleFor(customer => customer.Discount).NotEqual(0).When(customer => customer.HasDiscount);
    RuleFor(customer => customer.Address).Length(20, 250);
    RuleFor(customer => customer.Postcode).Must(BeAValidPostcode).WithMessage("Please specify a valid postcode");
  }

  private bool BeAValidPostcode(string postcode) {
    // custom postcode validating logic goes here
  }
}