Question

I am new to Entity Framework and hence this question may seem a little noobish.

I will try to explain my scenario with he Department-Employee example I have two tables “Department” and “Employee”. Department has an identity column DeptID. I am trying to create a new Department and add newly created Employees to it all in one go. Below is my code:

using (MyDB context = new MyDB())
{
Department dept = new Department(); 
dept.Name = "My Department"; 

Employee emp = new Employee(); 
emp.Name = "Emp Name"; 
emp.Department = dept; //Tried dept.Employees.Add(emp) also, same result
context.AddObject("Department", dept);
context.SaveChanges()
}

But for some reason, the record doesn’t get inserted. It throws an error in the second insert query.

Below are the queries:

INSERT INTO Department
           (Name)
VALUES     ('Dept1' /* @gp1 */);
SELECT ID
FROM   Department
WHERE  row_count() > 0
AND `ID` = last_insert_id()


--------------------------
INSERT INTO Employee
           (DeptID,
           Name)
VALUES     (19,
           'Name'); /* @gp1 */
SELECT id
FROM   Employee
WHERE  row_count() > 0
AND `id` = last_insert_id()

The error it throws is at line 4 of second query. So I am guessing something is wrong with the Identity thing. I am using MySQL.

Can anyone please explain what could be wrong?

EDIT: I have modified the SQL to suit this example. I can’t give my real table details.

Answer 1

What is the structure of your classes? I’d assume there is something slightly wrong and EF isn’t correctly building the model.

Also I had some problems with EF4.1 until I manually defined the key. The part of EF that ‘assumes’ which variable is your key doesn’t seem to work on some complex objects like objects that are derived from a base class and also fails in other cases.

Here is what I would expect your code to look like:

public class Department
{
    [Key]
    public Int64 DepartmentId { get; set;}

    public String Name { get; set;}
}

public class Employee
{
    [Key]
    public Int64 EmployeeId { get; set;}

    public String Name { get; set;}

    //Adding virtual here allows lazy loading of department
    public virtual Department Department {get; set;}
}


public class MyDatabase : DbContext
{
    DbSet<Department> Departments;
    DbSet<Employee> Employees;
}

I have an entire project at work that relies on Entity framework correctly mapping the above into a Many to One relationship and I’ve had no issues using code just as shown.