How do I update a nested property with Entity Framework

Question

I've got a ToDo class which has properties for Staff and Priority. If a user updates a ToDo item, changes the TaskName and maybe sets a new Priority how do I update the Priority property -

public class ToDo : BaseEntity
{
    public DateTime? DueDate { get; set; }
    public String Notes { get; set; }
    public virtual Priority Priority { get; set; }
    public virtual Staff Staff { get; set; }
    public String TaskName { get; set; }
}

In my WinForms code I have the following save method:

private void Save()    
{    
    var todo = new ToDo    
    {    
        ID = ToDoID,    
        Staff = ddlStaff.SelectedValue,    
        Priority = ddlPriority.SelectedValue,    
        TaskName = txtTaskName.Text.Trim(),
        Notes = txtNotes.Text.Trim(),
        DueDate = String.IsNullOrEmpty(txtDueDate.Text) ? DateTime.Now : DateTime.Parse(txtDueDate.Text.ToString())
};

 _todoController.SaveOrUpdate(todo);

}

The UI has drop down / combo lists for Staff and Priority, but ddlPriority.SelectedValue isn't a Priority object. I could call the database passing the SelectedValue to return the Priority object and then pass that into the ToDo object but that seems crazy just to create/maintain the relationship between the ToDo item and it's priority.

Answer 1

You could also instead have an extra property called PriorityId that you set and get. This is a very common scenario in web apps since they're stateless.

EDIT: You can also do something like this:

var selectedStaff = new Staff();
selectedStaff.Id = 2;
context.Staff.Attach(selectedStaff); // The important part.

var todo = new ToDo    
{    
    ID = ToDoID,    
    Staff = selectedStaff,
    Priority = ddlPriority.SelectedValue,    
    TaskName = txtTaskName.Text.Trim(),
    Notes = txtNotes.Text.Trim(),
    ....
}

context.SaveChanges();

Calling context.Staff.Attach(someStaffObject) basically adds the staff object to the context to allow it to be referenced. You have to be sure that you set the key property before calling Attach().