entity object cannot be referenced by multiple instances of IEntityChangeTracker. while adding related objects to entity in Entity Framework 4.1

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) { Pay…

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.

entity object cannot be referenced by multiple instances of IEntityChangeTracker. while adding related objects to entity in Entity Framework 4.1

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