Lazy loading properties after an insert

问题

I have a parent and child object. If I do the following

Child c = new Child();

c.ParentID = parentID;
context.Child.Add(c);
context.SaveChanges();

int i = c.Parent.ParentID; // throws an exception b/c Parent is null

Why is this doing this? If I get a new context (after saving), I can see Parent just fine.

回答1:

I guess you are working with lazy loading enabled. If you want that the navigation property gets populated after adding the object with the foreign key property to the context you must use the Create method of DbSet (instead of instantiating the object with new):

Child c = context.Child.Create();

With active lazy loading this will create a proxy object which ensures that the navigation property gets loaded.

来源：https://stackoverflow.com/questions/6312981/lazy-loading-properties-after-an-insert