asp.net mvc ObjectDisposedException with ef - asp.net-mvc-3

Question

I need some help with this error "The ObjectContext instance has been disposed and can no longer be used for operations that require a connection."
It's a asp.net mvc3, EF4, and ms sql.
Here is the razor with two dropdowns:
<div class="editRow">
#Html.DropDownListFor(m=>m.IndustryId, (SelectList)ViewBag.Industry, #Empower.Resource.General.ddlDefaultVal, new { #class = "ddl400" })
#Html.ValidationMessageFor(m => m.IndustryId)
</div>
<div class="editRow">
#Html.DropDownListFor(m=>m.ProvinceId, (SelectList)ViewBag.Province, #Empower.Resource.General.ddlDefaultVal, new {#class = "ddl400"})
#Html.ValidationMessageFor(m => m.ProvinceId)
</div>
Controller:
IndustryService indService = new IndustryService();
ViewBag.Industry = new SelectList(indService.GetAllIndustry(), "IndustryId", "IndustryName");
ProvinceService proService = new ProvinceService();
ViewBag.Province = new SelectList(proService.GetAllProvince(), "ProvinceId", "ProvinceName");
return View();
ProvinceService:
public IEnumerable<Province> GetAllProvince()
{
using (var context = DBContext.ObjectContext)
{
var pros = context.Provinces;
return pros;
}
}
IndustryService is identical as above...
public class DBContext
{
private static EmpowerDBEntities _empowerContext;
public static EmpowerDBEntities ObjectContext
{
get
{
if (_empowerContext == null)
_empowerContext = new EmpowerDBEntities();
return _empowerContext;
}
}
}
I know the problem occurs in second dropdown when it tries to retrive data while the connection is desposed by previous query. Please help me with this, thanks.

Answer 1

The fix is simple - convert to a .ToList() or First() before using. LINQ has deferred execution and tries to run this command after the context is disposed (when your object results are referenced) - not when you actually make the call.. You need to force it to run now while the context is in scope.
using (var context = DBContext.ObjectContext)
{
var pros = context.Provinces;
return pros.ToList();
}
Also - your code above is checking for null in the get accessor. However this object won't be null - it will be disposed, so you cannot do your check this way, you need to check if its null and not disposed.
public class DBContext
{
private static EmpowerDBEntities _empowerContext;
public static EmpowerDBEntities ObjectContext
{
get
{
if (_empowerContext == null || _empowerContext.IsDisposed())
_empowerContext = new EmpowerDBEntities();
return _empowerContext;
}
}
}
something like that anyways :)

Answer 2

I ran into a similar problem. I had been following this pattern, which I had seen in many code examples on the web:
public ActionResult Show(int id)
{
using (var db = new MyDbContext())
{
var thing = db.Things.Find(id);
return View(thing);
}
}
However, this was causing the ObjectDisposedException listed above whenever I tried to access anything that hadn't been loaded into memory in the View code (in particular, one-to-many relationships in the main view model).
I found a different pattern in this example:
public class MyController : Controller
{
private MyDbContext _db;
public MyController()
{
_db = new MyDbContext();
}
public ActionResult Show(int id)
{
// Do work such as...
var thing = _db.Things.Find(id);
return View(thing);
}
protected override void Dispose(bool disposing)
{
_db.Dispose();
base.Dispose(disposing);
}
}
This pattern keeps the database connection alive until the View has finished rendering, and neatly disposes of it when the Controller itself is disposed.

Answer 3

Here is the problem when you are using
using(var context=new CustomerContext())
{
return View(context.Customers.ToList());
}
when the block of code executes all references are disposed that you are lazzy loading so that's why it is throwing this error.
so i used
return View(context.Customers.ToList()) directly it will work perfectly fine.