Question

I have a class, called Permissions, it has a few subclasses (and some properties), Group and Group.Permission.

Now, I CAN do the following

Permissions u = new Permissions();
u.userId = (Guid)user.ProviderUserKey;
List<int> groups = getGroupsForUserId(u.userId.ToString());

List<Permissions.Group> groupItems = new List<Permissions.Group>();

foreach (int g in groups)
{
    Permissions.Group groupItem = new Permissions.Group();
    groupItem.group_id = g;
    groupItem.Records = getRecordsForGroupId(g);
    groupItem.Permissions = getPermissionsForGroupId(g);

    groupItems.Add(groupItem);
}
u.Groups = groupItems;

However, I CAN’T do this:

Permissions u = new Permissions();
u.userId = (Guid)user.ProviderUserKey;
List<int> groups = getGroupsForUserId(u.userId.ToString());

foreach (int g in groups)
{
    Permissions.Group groupItem = new Permissions.Group();
    groupItem.group_id = g;
    groupItem.Records = getRecordsForGroupId(g);
    groupItem.Permissions = getPermissionsForGroupId(g);

    u.Groups.Add(groupItem);
}

My question, why?

I created a new Permissions.Group object, added the values and then added it to the u object’s list of Groups. To my mind that should work, however I assume I’ve not wired something up in my class? My class just is a list of properties property_name { get; set; } so isn’t anything exotic really.

Trying the latter, I get a NullReferenceException on the line u.Groups.Add(groupItem);

Answer 1

You probably need to initialize Permissions.Groups in your Permissions constructor:

public class Permissions
{
    public Permissions()
    {
         Groups = new List<Group>();
    }

    public ICollection<Group> Groups { get; set; }
}