Entity Framework Code First Read and write bridge table

Question

I just have a simple question about bridge(link) table. I have two tables that has a many-to-many relation and Visual Studio auto generates the bridge table with the primary key from those two tables. I'm a little bit confused about how to read and write data from and to the tables.

When I read data, do I query and fetch data from just one or both of the two tables that has a many-to-many relation? But how do I handle the bridge table?

And when I write data, the same thing here, do I save the data to one or both of the two tables that has a many-to-many relationship? And how do I know when I should save to the bridge table?

Very confusing and I can't find any good tutorial with code examples that I can learn from. Since I created Controllers with read and write Views, I thought this matter was taken care of in the auto genrated code, but since the bridge table is empty despite that I have added data to the other tables, I need to ask this question to get some clarity about this! Preciate if any could tell me how it works with simple example or link. Thanks!

EDIT: Table Entities for some of the tables. I'm doing this project with ASP.NET MVC.

public class Order
{
public int ID { get; set; }
public string Name { get; set; }
public int? ManufacturerID { get; set; }
public virtual Manufacturer Manufacturer { get; set; }
public virtual ICollection<Employee> Employees { get; set; }
}

public class Employee
{
public int ID { get; set; }
public string Name { get; set; }
public int EmployeeNumber { get; set; }
public virtual ICollection<Timeunit> Timeunits { get; set; }
public virtual ICollection<Order> Orders { get; set; }
}

Answer 1

The above relationship will create a bridge table like:

public class OrderEmployeeEnrollments{
  public int OrderId {get;set;}
  public int EmployeeId {get;set;}
}

To Read data from Order table for an employee:

using (var context = new YourContext())
{
  var order= context.Orders.Where(o => o.OrderEmployeeEnrollments.
               Any(e => e.Employee.EmployeeId == employeeId );
}

To insert in Order table:

using (var context = new YourContext())
{
   var order= new Order{
     Name="",
     ManufacturerID= 2 ,
     Manufacturer = new Manufacturer { // create  Manufacturer },
     Employees = new List<Employee> { // create list}    
  }
  context.Orders.Add(order);
  context.SaveChanges();
}

To insert 'Order' table with an existing employee:

 using (var context = new YourContext())
{
   var order= new Order{
     Name="",
     ManufacturerID= 2 ,         
     Employees = context.Employees.Where(e=> e.Name=="Name")    
  }
  context.Orders.Add(order);
  context.SaveChanges();
}

Hope this will help :)

Answer 2

Entity Framework works in a way that you don't have to concern yourself with the bridge table. It handles that for you as long as you have defined the relationship between entities.

In this case:

public class Order
{
    ...
    public virtual ICollection<Employee> Employees { get; set; }
}

public class Employee
{
    ...
    public virtual ICollection<Order> Orders { get; set; }
}

Here's an example..
WRITE:

    Order order = new Order();
    order.Name = "foo";
    order.Employees = _ctx.Employees.Where(e => id > 0 && id <= 5);
    _ctx.Orders.Add(order);
    _ctx.SaveChanges();

READ:

    List<Employee> employees = _ctx.Employees.Where(e => id > 0 && id <= 5);

    foreach(Employee emp in employees)
    {
       Order theOrder = emp.Orders.FirstOrDefault(o => o.ID == order.ID);
       if(theOrder != null)
       {
           Console.WriteLine("Employee {0} has served order {1}", emp.ID, theOrder.ID);
       }
    }