MVC 5一对多虚拟ICollection返回null吗？

Question

I have a model which looks like this

public class MyModel
{
....
public virtual ICollection<Comm_ent> Comments { get; set; }
}

and the submodels look like

public class Comm_ent 
{
...
public virtual My_Model MyModel{ get;set;}
}

In my Comm_ent Datatable I have a MyModelId key created by migration but when I do

public actionresult MyModelIndex(int? id)
{
var mymodel = _context.MyModels.singleordefault(u => u.Id == id)
return View(mymodel);
}

The @Model.Comments is null even though I have entries in Comm_ent datatable . This was working in MVC4 but after upgrade to MVC5 it returns null result. Any ideas how to do this in MVC5?

Answer 1

Try to add Include method:

public actionresult MyModelIndex(int? id)
{
var mymodel = _context.MyModels.Include(u => u.Comments).singleordefault(u => u.Id == id)
return View(mymodel);
}

Don't forget to add the following using statement:

using System.Data.Entity;

Answer 2

Try initializing the collection in the constructor for MyModel:

public MyModel(){
   Comments = new HashSet<Comm_ent>();
}