Creating related attributes when creating new instance of class MVC 4 - Entity Framework

Question

I am just getting into MVC 4 and Entity Framework 5 and want to know if what I am doing is correct?

I have a UserObject and a JobObject, the jobObject has a reference to a User Object.

public class Job
{
    public int id { get; set; }
    public virtual MyUser User { get; set; }
    public JobType JobType { get; set; }
}

When I want to create an instance of the Job I am passing in the query string a parameter UserID, but the Job only deals with an instance of MyUser.

Is the following the correct way to associate the user to the job?

[HttpPost]
public ActionResult Create(Job job, int userid)
{
   if (ModelState.IsValid)
   {    
     MyUser staffmember = db.MyUsers.Find(userid);
     if (staffmember == null)
      {
        return View("StaffMemberNotFound");
      }
     job.User = staffmember;
     db.Jobs.Add(job);
     db.SaveChanges(); 
   }
}

Or is there a better way to associate the user to the job?

NinjaNye · Accepted Answer · 2013-04-02 17:46:07Z

1

Your way will work but I prefer to simply work with ids if possible.

What I would suggest is that you add a MyUserId property to your Job class (remember to update the database if you are using codefirst):

public class Job
{
    public int id { get; set; }
    [ForeignKey("User")]
    public int MyUserId { get; set: }

    public virtual MyUser User { get; set; }
    public JobType JobType { get; set; }
}

Then simply populate the MyUserId. You can also change your check to simply check if the id exists as apposed to finding an object and letting EF map that to a class before returning it to you

[HttpPost]
public ActionResult Create(Job job, int userid)
{
   if (ModelState.IsValid)
   {    
     if (!db.MyUsers.Any(u => u.Id == userid)
     {
        return View("StaffMemberNotFound");
     }

     job.MyUserId = userid;
     db.Jobs.Add(job);
     db.SaveChanges(); 
   }
}

EF will do the rest of the mapping for you when you next retrieve the record from the database.

edited Apr 2, 2013 at 17:46

answered Apr 2, 2013 at 16:42

NinjaNye

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3 Comments

Chris Over a year ago

I tried what you suggested (I also deleted the DB so as to start out with a clean DB) but I have one of two issues. If I add MyUserId then I end up in the DB with two different IDs ie two fields. MyUserID and MyUser_ID (Entity framework generated id for the user) and my redundant MyUserId If I create a field called MyUser_ID I get an error about creating two fields with the same name? What am I doing wrong?

NinjaNye Over a year ago

My apologies, I thought ef convention would have picked this up. On your MyUserId property add [ForeignKey("MyUser")]. I'll update my answer

NinjaNye Over a year ago

UPDATE: Use [ForeignKey("User")] above, not [ForeignKey("MyUser")] as previously stated. My answer is now up to date

Philip Tenn · Accepted Answer · 2013-04-02 19:11:15Z

Your approach works fine, the only small optmization you could make is not taking the "retrieval hit" of MyUser staffmember = db.MyUsers.Find(userid); since you already have the userid.

I am using ASP.NET MVC 4 and Entity Framework 5.0, and here is my code (different model objects, but same intent as what you are doing).

Note: I let EF generate my model classes by right-clicking on the Models folder and choosing Add->ADO.NET Entity Data Model in VS.NET 2012.

Store.Models.Product

namespace Store.Models
{
    using System;
    using System.Collections.Generic;

    public partial class Product
    {
        public long Id { get; set; }
        public string ProductName { get; set; }
        public decimal Price { get; set; }
        public int Quantity { get; set; }
        public System.DateTime DateAdded { get; set; }
        public Nullable<long> CategoryId { get; set; }

        public virtual Category Category { get; set; }
    }
}

Store.Models.Category

namespace Store.Models
{
    using System;
    using System.Collections.Generic;

    public partial class Category
    {
        public Category()
        {
            this.Products = new HashSet<Product>();
        }

        public long Id { get; set; }
        public string CategoryName { get; set; }
        public System.DateTime DateAdded { get; set; }

        public virtual ICollection<Product> Products { get; set; }
    }
}

On my Create.cshtml page, I have the User select the CategoryId from the drop-down list. This Category Id is bound to Product.CategoryId. All I do in my method is this:

ProductController

public class ProductController : Controller
{
    ...
    [HttpPost]
    public ActionResult Create(Product product)
    {
        product.DateAdded = DateTime.Now;
        if (dbContext != null)
        {
            dbContext.Products.Add(product);
            dbContext.SaveChanges();
        }
        return RedirectToAction("Index");
    }
    ...
}

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