How to select just some fields from a table in EF - asp.net-mvc

Question

I have a table with 9 columns in database and I want to be able to load only some fields of it if I need.
How can I do this with Entity Framework 4 please?
e.g. My table has these fields:
ID, FirstName, LastName, FotherName, BirthDate, Mobile, Email
and I want to be able to fetch just these columns:
ID, FirstName, LastName
My project is an ASP.NET MVC 3 application, with SQLServer 2008 Express and EF 4.1.

Answer 1

Assume you have a table with this model:
public class User{
public int ID {get; set;}
public string NickName {get; set;}
public string FirstName {get; set;}
public string LastName {get; set;}
public string FotherName {get; set;}
public DateTime BirthDate {get; set;}
public string Mobile {get; set;}
public string Email {get; set;}
public string Password {get; set;}
}
Now, you want fetch just ID, FirstName, LastName, and FotherName. You can do it in 2 way; The first way is fetch them as an anonymous object, look:
var user = entityContext.Users.Where(u => u.ID == id)
.Select(u => new {
ID = u.ID,
FirstName = u.FirstName,
LastName = u.LastName,
FotherName = u.FotherName
}).Single();
Now, your return-value-type is anonymous, you can work with it such as:
var i = user.ID;
// or
var s = user.FirstName;
In another way (for example when you want to pass the object as an Model to a View), you can define a new class, (i.e. UserViewModel), and when you select the object, select it as a UserViewModel. look:
public class UserViewModel{
public int ID {get; set;}
public string NickName {get; set;}
public string FirstName {get; set;}
public string LastName {get; set;}
public string FotherName {get; set;}
}
and in query, take this:
var user = entityContext.Users.Where(u => u.ID == id)
.Select(u => new UserViewModel {
ID = u.ID,
FirstName = u.FirstName,
LastName = u.LastName,
FotherName = u.FotherName
}).Single();
Look that just ONE difference is between them, in labda expression, instead of u => new {}
we are using u => new UserViewModel{}. Good luck.

Answer 2

There can be many ways to do this job, but using Automapper NuGet package is the most simple one I have experienced.
First: Install Autmapper NuGet package for your project from NuGet package explorer.
Second: Make a simple ViewModel, which contains only required attributes:
public class UserViewModel {
public int ID {get; set;}
public string FirstName {get; set;}
public string LastName {get; set;}
}
Third: Initialize your your mapper only for once in app_start class like:
namespace SampleProject.App_Start {
public class AutoMapperConfig {
public static void Initializer() {
AutoMapper.Mapper.Initialize(cfg => {
cfg.CreateMap<User, UserViewModel>()
});
}
}
}
Fourth: Add it's entry in Global.asax.cs:
namespace SampleProject
{
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
GlobalConfiguration.Configure(WebApiConfig.Register);
FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
RouteConfig.RegisterRoutes(RouteTable.Routes);
BundleConfig.RegisterBundles(BundleTable.Bundles);
// AutoMapper Initializer
App_Start.AutoMapperConfig.Initializer();
}
}
}
Fifth: Use it in your controller where you want like this:
namespace SampleProject.Controllers
{
public class UsersController : Controller
{
private DataContext db = new DataContext();
public ActionResult Index()(
var model = AutoMapper.Mapper.Map<List<UserViewModel>>(db.User.ToList());
return View(model);
}
}
}
Last: You can create as many maps as you want between your Models and ViewModels by initializing them once in the app_start's AutoMapperConfig class and use them where you want with a simple line of code.
Also you can find a lot of help about Automapper if you search about it. Its main website is here.
Important:
I am a developer of ASP.NET MVC 5. Automapper works fine for me every time. I cannot check it on MVC 3 or older than MVC 5.