Multiple instances of IEntityChangeTracker cannot refer to the same entity object. In Entity Framework 4.1, when adding linked objects to an entity,

ado.net asp.net c# entity-framework foreign-keys

Question

I am trying to save Employee details, which has references with City. But everytime I try to save my contact, which is validated I get the exception "ADO.Net Entity Framework An entity object cannot be referenced by multiple instances of IEntityChangeTracker"

I had read so many post but still not getting the exact idea of what to do... my Save button click code is given below

protected void Button1_Click(object sender, EventArgs e)
    {
        EmployeeService es = new EmployeeService();
        CityService cs = new CityService();

        DateTime dt = new DateTime(2008, 12, 12);
        Payroll.Entities.Employee e1 = new Payroll.Entities.Employee();

        Payroll.Entities.City city1 = cs.SelectCity(Convert.ToInt64(cmbCity.SelectedItem.Value));

        e1.Name = "Archana";
        e1.Title = "aaaa";
        e1.BirthDate = dt;
        e1.Gender = "F";
        e1.HireDate = dt;
        e1.MaritalStatus = "M";
        e1.City = city1;        

        es.AddEmpoyee(e1,city1);
    }

and Employeeservice Code

public string AddEmpoyee(Payroll.Entities.Employee e1, Payroll.Entities.City c1)
        {
            Payroll_DAO1 payrollDAO = new Payroll_DAO1();
            payrollDAO.AddToEmployee(e1);  //Here I am getting Error..
            payrollDAO.SaveChanges();
            return "SUCCESS";
        }
1
163
7/9/2012 5:04:04 PM

Accepted Answer

Because these two lines ...

EmployeeService es = new EmployeeService();
CityService cs = new CityService();

... don't take a parameter in the constructor, I guess that you create a context within the classes. When you load the city1...

Payroll.Entities.City city1 = cs.SelectCity(...);

...you attach the city1 to the context in CityService. Later you add a city1 as a reference to the new Employee e1 and add e1 including this reference to city1 to the context in EmployeeService. As a result you have city1 attached to two different context which is what the exception complains about.

You can fix this by creating a context outside of the service classes and injecting and using it in both services:

EmployeeService es = new EmployeeService(context);
CityService cs = new CityService(context); // same context instance

Your service classes look a bit like repositories which are responsible for only a single entity type. In such a case you will always have trouble as soon as relationships between entities are involved when you use separate contexts for the services.

You can also create a single service which is responsible for a set of closely related entities, like an EmployeeCityService (which has a single context) and delegate the whole operation in your Button1_Click method to a method of this service.

239
4/17/2012 3:35:29 PM

Popular Answer

Steps to reproduce can be simplified to this:

var contextOne = new EntityContext();
var contextTwo = new EntityContext();

var user = contextOne.Users.FirstOrDefault();

var group = new Group();
group.User = user;

contextTwo.Groups.Add(group);
contextTwo.SaveChanges();

Code without error:

var context = new EntityContext();

var user = context.Users.FirstOrDefault();

var group = new Group();
group.User = user; // Be careful when you set entity properties. 
// Be sure that all objects came from the same context

context.Groups.Add(group);
context.SaveChanges();

Using only one EntityContext can solve this. Refer to other answers for other solutions.



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