Question

What is the correct way to insert/update a row using Entity Framework?

I know this 3 methods:

1 – using Attach

var newSale = _context.ST_Sales.FirstOrDefault(x => x.SaleId == saleId);
newSale.Hours = 2;
_context.ST_Sales.Attach(newSale);
_context.ObjectStateManager.ChangeObjectState(newSale, EntityState.Modified);
_context.SaveChanges();

2 – using ApplyCurrentValues

var newSale = _context.ST_Sales.FirstOrDefault(x => x.SaleId == saleId);
newSale.Hours = 2;
_context.ST_Sales.ApplyCurrentValues(newSale);
_context.SaveChanges();

3 – using EF logic

var newSale = _context.ST_Sales.FirstOrDefault(x => x.SaleId == saleId);
newSale.Hours = 2;
_context.SaveChanges(); // EF tracks the newSale obj and knows that was changed

And to insert there are one more method witch uses the AddObject

var newSale = new ST_Sales();
newSale.Hours = 2;
_context.ST_Sales.AddObject(newSale);
_context.SaveChanges();

The problem I’m facing is an error on the EF saying that the modified row is still in memory.

My scenario:

• 20 users can add sales to their own company.

I have a simple table relation:

tbl_Companies { CompanyId, Name }
tbl_Sales     { CompanyId, Hours, Amount }

my Edit View simple get’s a sales collection of the current week as

var model = _context.ST_Sales.Where(x => x.CompanyId == 2);
return View(model);

and on the HttpPost Action I simply loop through each one and save the db changes like

[HttpPost]
public ViewResult Index(List<ST_Sales> model)

and

bool newSale = false;
foreach( var s in model ) { // let's loop through all

    newSale = false;

    var sale = _context.ST_Sales.FirstOrDefault(x => x.SaleId == s.SaleId);
    if( sale == null) {

        // sale was not found, let's add it (this happens for todays date
        //    as there is no info yet in the db, but we need to add today's info)

        sale = new ST_Sale();
        sale.Company.Id = currentLoggedInUser.companyId;

        newSale = true;  // let's say it's a new sale so we can add the new object to the changes to commit
    }

    sale.Hours = s.Hours;
    sale.Amount = s.Amount;

    if( newSale ) {
        // it's a new sale, let's add the obj to our Entity
        _context.ST_Sales.AddObject(sale);
    } 
    else {
        // no need to do anything, EF is tracking the changes of existing objects
    }
}

_context.SaveChanges();

This works fine for one user… but if I logout and login with a different user, and I can see in the breakpoint that the companyId value is different, soon I commit the changes to be saved I get the weird error:

An entity object cannot be referenced by multiple instances of IEntityChangeTracker.

What am I doing wrong?

---

I’m creating a new instance in the Controller level like:

public class SalesController : Controller
{
    private SalesTrackerRepository db = SalesTrackerRepository.Instance;

    ...
}

and using the source from Sams Code

---

Also, I used Rick Strahl code and ending up using:

public class SalesController : Controller
{
    private SalesTrackerRepository db = 
            SalesTrackerRepositoryFactory.GetWebRequestScopedDataContext<SalesTrackerRepository>();

    ....

}

And I keep getting the same error 🙁

---

My tests are based in the same machine using Chrome and Opera with both different credentials.

How can I get this error on such test?

Answer 1

Got the bugger!

I was using MemoryCache to cache some results and realized that I was using that cache to request an EntityKey.

My advise: Please check if in your project you really want to deal with all this workarounds!