I have a strange error. I'm experimenting with a .NET 4.5 Web API, Entity Framework and MS SQL Server. I've already created the database and set up the correct primary and foreign keys and relationships.

I've created a .edmx model and imported two tables: Employee and Department. A department can have many employees and this relationship exists. I created a new controller called EmployeeController using the scaffolding options to create an API controller with read/write actions using Entity Framework. In the wizard, selected Employee as the model and the correct entity for the data context.

The method that is created looks like this:

// GET api/Employee
public IEnumerable<Employee> GetEmployees()
{
    var employees = db.Employees.Include(e => e.Department);
    return employees.AsEnumerable();
}

When I call my API via /api/Employee, I get this error:

...The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; ...System.InvalidOperationException","StackTrace":null,"InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Self referencing loop detected with type 'System.Data.Entity.DynamicProxies.Employee_5D80AD978BC68A1D8BD675852F94E8B550F4CB150ADB8649E8998B7F95422552'. Path '[0].Department.Employees'.","ExceptionType":"Newtonsoft.Json.JsonSerializationException","StackTrace":" ...

Why is it self referencing [0].Department.Employees? That doesn't make a whole lot of sense. I would expect this to happen if I had circular referencing in my database but this is a very simple example. What could be going wrong?