Exception NullReferenceException in controller (asp.net mvc) - asp.net-mvc

Question

There are Supplier model and User model in my project, every Supplier has a few Users
Supplier model
public class SupplierRow
{
public Guid Id { get; set; }
public string FullName { get; set; }
public bool Subscribed { get; set; }
public bool Active { get; set; }
public int Visits { get; set; }
public List<UserRow> Users { get; set; }
public bool AllInactive
{
get
{
foreach (UserRow ur in Users)
{
if (ur.Status == 1) return false;
}
return true;
}
}
}
and User model
public class UserRow
{
public Guid Id { get; set; }
public string FullName { get; set; }
public string Name { get; set; }
public string Email { get; set; }
public int Status { get; set; }
public int Role { get; set; }
public Guid SupplierId { get; set; }
}
then I use my models in controller
public ActionResult Grid(bool? active)
{
var suppliers = Context.Suppliers.AsNoTracking()
.WhereIf(active != null, e => e.Active == active)
.Select(e => new SupplierRow
{
Id = e.Id,
FullName = e.FullName,
Active = e.Active,
Visits = e.Visits,
})
.ToList();
List<Guid> supplierIds = new List<Guid>();
foreach (SupplierRow sr in suppliers)
{
supplierIds.Add(sr.Id);
}
var users = Context.Users.AsNoTracking()
.Where(e => supplierIds.Contains(e.SupplierId.Value))
.Select(e => new UserRow
{
Id = e.Id,
FullName = e.FullName,
Email = e.Email,
Name = e.Name,
Status = e.Status,
Role = e.Role,
SupplierId = e.SupplierId.Value
}).ToList();
foreach (UserRow ur in users)
{
foreach (SupplierRow sr in suppliers)
{
if (ur.SupplierId == sr.Id)
{
sr.Users.Add(ur);
}
}
}
return PartialView("_Grid", suppliers);
}
but when I try to debug my project I get some exception here
What's wrong? How can I fix that?

Answer 1

Your Users list are not initialized. Create a new list before accessing it Users = new List<UserRow>(); You can change the SupplierRow class:
public class SupplierRow {
private List<UserRow> users = new List<UserRow>();
public List<UserRow> Users
{
get { return users; }
set { users = value; }
}
...
}
or in the constructor:
public class SupplierRow
{
public SupplierRow()
{
Users = new List<UserRow>();
}
public List<UserRow> Users { get; set; }
...
}
or before accessing it:
foreach (UserRow ur in users)
{
foreach (SupplierRow sr in suppliers)
{
sr.Users = new List<UserRow>();
if (ur.SupplierId == sr.Id)
{
sr.Users.Add(ur);
}
}
}
or you can just use linq:
foreach (SupplierRow sr in suppliers)
{
sr.Users = users.Where(user => user.SupplierId == sr.Id);
}
return PartialView("_Grid", suppliers);