实体框架6-延迟加载不起作用

Question

This is my first time using EF. As such I may have missed something simple that is preventing lazy loading of my BClass. When I load AClass the 'B' property is null. I would have expected it to be populated as persisted.

For my example I have two simple classes:

public class AClass
{
    public AClass()
    {
        Id = Guid.NewGuid();
        B = new BClass();
    }
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public Guid Id { get; set; }
    public string Name { get; set; }
    public virtual BClass B { get; set; }
}

public class BClass
{
    public BClass()
    {
        Id = Guid.NewGuid();
    }
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public Guid Id { get; set; }
    public string Description { get; set; }
}

In the 'Context' class:

public DbSet<AClass> AClasses { get; set; }
public DbSet<BClass> BClasses { get; set; }

Below is a simple test. I was expecting xB would be loaded. Instead it is null?

using (var db = new TestContext())
{
    AClass a = new AClass();
    a.Name = "AClass";
    a.B.Description = "BClass Description Goes Here!";
    db.AClasses.Add(a);
    db.SaveChanges(); // Works. Confirmed both a and a.B are persisted to the database
}

using (var db = new TestContext())
{
    AClass x = db.AClasses.Where(a => a.Name == "AClass").FirstOrDefault();
    System.Console.WriteLine(x.Name);
    System.Console.WriteLine(x.B.Description); // x.B is null. Expected it to load and the .Description property to be "BClass Description Goes Here!"
}

Changes were persisted to the database correctly. I can't post the screen shot yet.

From AClass table:

Id  Name    B_Id
B7937E1B-9CC0-4318-B179-0D54B23B6CDA    AClass  560D066B-4848-454D-B92C-F6AE4232057E

From BClass table:

Id  Description
560D066B-4848-454D-B92C-F6AE4232057E    BClass Description Goes Here!

Entity Framework Version: 6.0.0.0

Answer 1

Remove B initialization form class AClass :

public AClass()
{
    Id = Guid.NewGuid();
    //B = new BClass();
}

The initialization causes the entity framework think that you assigned new value to B property of AClass and does not assign it with a proxy.