Using Viewmodel to populate sql data and add columns - asp.net-mvc

Question

I would like to take a model of a table and make a viewmodel with additions fields, then populate it as a view. How do I do this in the controller? When it was just a model it worked but I'm not sure how to do the same thing when it's a viewmodel. I'm new to asp.net mvc so any help would be appreciated.
Model:
public partial class tblTag
{
public int TagId { get; set; }
public string TagName { get; set; }
}
ViewModel:
public class tblTagViewModel
{
public string TagName { get; set; }
public string TagNameClr
{
get
{
if (TagName == "Test")
{
return "green";
}
else
{
return "red";
}
}
}
}
Controller:
Cannot implicitly convert type 'System.Data.Entity.DbSet<_1MvcSqlServer.Models.tblTag>' to '_1MvcSqlServer.ViewModel.tblTagViewModel'
Now that it's a viewmodel the structure from entities is different, I assume that is the problem. How do I resolve this?
private testEntities db = new testEntities();
public ActionResult Test()
{
ViewModel.tblTagViewModel model = new ViewModel.tblTagViewModel();
model = db.tblTags;
return(model);
}
Here is what I ended up with to get it to work. Is this the correct method?
public ActionResult Test()
{
List<ViewModel.tblTagViewModel> list = new List<ViewModel.tblTagViewModel>();
var model = new ViewModel.tblTagViewModel();
foreach(tblTag p in db.tblTags)
{
ViewModel.tblTagViewModel nw = new ViewModel.tblTagViewModel();
nw.TagName = p.TagName;
list.Add(nw);
}
return View(list);
}

Answer 1

Correct method - create Business layer, which would get data from DB layer and pass this data to View layer (and vice versa, get data from View layer and pass to DB layer).
Also, I recommend to look at IoC (DI) approach :
Business Layer:
First at all, you create new ClassLibrary project and create Business layer POCO classes and an abstraction of your repository:
/// <summary>
/// this is a Business layer class, which is very similar on EF class
/// </summary>
public class Tag
{
public int TagId { get; set; }
public string TagName { get; set; }
}
public interface IRepository
{
List<Tag> GetTagList();
}
Then you create Service:
public class Service
{
private readonly IRepository _repository;
public Service(IRepository repository)
{
if (repository == null)
throw new ArgumentNullException("repository");
_repository = repository;
}
public List<Tag> GetTagList()
{
return _repository.GetTagList();
}
}
on this stage you have compiled version of Business layer. You can add all complex logic of your application and test it. Attent, without DB amd View parts!
Next step - create DB layer
DB Layer:
Create one more Class Library in your solution, add link to BL project and add code like this:
public class EFRepository : IRepository
{
private ... _db;
public EFRepository()
{
.....
}
public List<Tag> GetTagList()
{
var tags = (from i in _db.tblTags select new Tag { TagId = i.TagId, TagName = i.TagName }).ToList();
}
}
so, you have DB and BL layers. And your BL layer is not depend on DB layer, vice versa, DB layer is depend on BL layer .And it's a correct approach, business logic of your application should not be depended on DB!
The last step - View Layer.
View Layer
You can separate View Layer to different project too. I do it inside my ASP.NET MVC application. Add references to DB and BL projects
public class tblTagViewModel
{
public string TagName { get; set; }
public string TagNameClr
{
get
{
if (TagName == "Test")
{
return "green";
}
else
{
return "red";
}
}
}
}
and your controller:
public class HomeController : Controller
{
private readonly Service _service;
public HomeController(IRepository repository)
{
if (repository == null)
throw new ArgumentNullException("repository");
_service = new Service(repository);
}
public ActionResult Test()
{
List<ViewModel.tblTagViewModel> list = new List<ViewModel.tblTagViewModel>();
vat taglist = _service.GetTagList();
foreach (tblTag p in taglist)
{
ViewModel.tblTagViewModel nw = new ViewModel.tblTagViewModel();
nw.TagName = p.TagName;
list.Add(nw);
}
return View(list);
}
}
and, the last step, set DB implementation to your web app:
public class MyControllerFactory : DefaultControllerFactory
{
protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
{
var efRepository = new EFRepository();
if (controllerType == typeof(HomeController))
{
return new HomeController(efRepository );
}
return base.GetControllerInstance(requestContext, controllerType);
}
pay attention, that your web-application is not depend on DB layer, it depends only on BL layer (this is logical too). Only one place to set EFRepository in your web application - in controller factory.
With this approach you can easily change EFRepository to another implementation of IRepository, with different DB or even fake DB. You can test any part of your application without unnecessary relationships. You have strong and correct architecture, where your application depend on business logic layer and not depend on DB layer etc. Any changes in DB layer or View layer are not affect on logic layer
For mapping similar POCO classes (i.e BL and DB, BL and View classes) with many properties you can user Automapper