Question

I have a solution with existing data access layer(class library) with models in it. I have web forms application which calls this library to do crud operations on db using stored procs. If I want to convert this webform application into an MVC 3 application what should be my approach for migration. I don’t want to use entity framework and would like to continue using my dataaccess layer for models and operations on model as the same library is being used by my webservices project. Any pointers.

Answer 1

Sure View Models are meant for moving data to/from views to your business/data layer. If you already have models defined in your data layer, then you can either have your view model inherit your data model or have the view consume it directly.

I’d recommend inheriting and then using new properties in your view model to set the underlying (inherited) properties. That way you can add validation attributes to your new properties and enforce validation at the client & server before setting the inherited properties and updating the database.

As an example, if your data layer has:

public class Person
{
    public string Name {get; set;}
    public string Email {get; set;}
}

Then in your View Model you can use:

public class VPerson : Person
{
    [Required(ErrorMessage = "Name is required.")]
    [StringLength(50, ErrorMessage = "Name cannot be longer than 50 characters.")]
    public string VName { get; set; }

    [Required(ErrorMessage = "Email is required.")]
    [RegularExpression(Settings.EmailRegex, ErrorMessage = "Email Address is not valid.")]
    [StringLength(50, ErrorMessage = "Email cannot be longer than 50 characters.")]
    public string VEmail { get; set; }

    public void SavePerson()
    {
        Name = VName;
        Email = VEmail;
        // update the DB
    }
}

Properties that don’t need validation (i.e. DropDown lists) you can use directly.

You don’t actually need to inherit, and could just call your data layer in SavePerson.