Question

I have an app with Entity Framework 5 code-first this is sample of my classes:

public partial class PlaningCourseAssistant 
{
    public PlaningCourseAssistant() {}
    public int ID { get; set; }
    public int PlaningCourseID { get; set; }
    public int AssistantID { get; set; }

    public virtual PlaningCourse PlaningCourse { get; set; }
    public virtual Teacher Assistant { get; set; }
} 

And

public class Teacher 
{
    public Teacher() 
    {
        ...
        this.PlaningCourseAssistants = new HashSet<PlaningCourseAssistant>();
    }
    public int ID { get; set; }
    public string Name{ get; set; }
    ....
    public virtual ICollection<PlaningCourseAssistant> PlaningCourseAssistants { get; set; }
}

And

public partial class PlaningCourse 
{
    public PlaningCourse() 
    {
    ...
        this.PlaningCourseAssistants = new HashSet<PlaningCourseAssistant>();
    }
    public int ID { get; set; }
    public string Title { get; set; }
    ...
    public virtual ICollection<PlaningCourseAssistant> PlaningCourseAssistants { get; set; }
}

when i add a new object to my PlaningCourseAssistant like this :

var pcb = new PlaningCourseAssistant 
{
    PlaningCourseID = CourseID,
    AssistantID = assistantID,
};
try 
{
    planingCourseAssistantService.Add(pcb);
    uow.SaveChanges();
} catch { }

afterward when i want to get PlaningCourseAssistant list, the added PlaningCourseAssistant‘s Assistant navigation key is null.

Why this happen? And how can I fix this?

Answer 1

EF can not lazy load the ‘Assistant’ property because the PlaningCourseAssistant instance you are using is not a proxy created by EF.

You can either use explicit loading

context.Entry(pcb).Reference(p => p.Assistant).Load();
context.Entry(pcb.Assistant).Collection(p => p.PlaningCourseAssistant).Load();

Or let EF create a proxy instance of PlaningCourseAssistant

var pcb = context.PlaningCourseAssistants.Create();