Question

I was wondering if this code is good enough or if there are glaring newbie no-no’s.

Basically I’m populating a TreeView listing all Departments in my database. Here is the Entity Framework model:

Here is the code in question:

private void button1_Click(object sender, EventArgs e)
{            
    DepartmentRepository repo = new DepartmentRepository();
    var parentDepartments = repo.FindAllDepartments()
                          .Where(d => d.IDParentDepartment == null)
                          .ToList();
    foreach (var parent in parentDepartments)
    {           
        TreeNode node = new TreeNode(parent.Name); 
        treeView1.Nodes.Add(node);

        var children = repo.FindAllDepartments()
                     .Where(x => x.IDParentDepartment == parent.ID)
                     .ToList();
        foreach (var child in children)
        {
            node.Nodes.Add(child.Name);                       
        }                
    }
}

EDIT:

Good suggestions so far. Working with the entire collection makes sense I guess. But what happens if the collection is huge as in 200,000 entries? Wouldn’t this break my software?

DepartmentRepository repo = new DepartmentRepository();
var entries = repo.FindAllDepartments();

var parentDepartments = entries
                      .Where(d => d.IDParentDepartment == null)
                      .ToList();
foreach (var parent in parentDepartments)
{
    TreeNode node = new TreeNode(parent.Name);
    treeView1.Nodes.Add(node);

    var children = entries.Where(x => x.IDParentDepartment == parent.ID)
                          .ToList();
    foreach (var child in children)
    {
        node.Nodes.Add(child.Name);
    }
}

Answer 1

That looks ok to me, but think about a collection of hundreds of thousands nodes. The best way to do that is asynchronous loading – please notice, that do don’t necassarily have to load all elements at the same time. Your tree view can be collapsed by default and you can load additional levels as the user expands tree’s nodes. Let’s consider such case: you have a root node containing 100 nodes and each of these nodes contains at least 1000 nodes. 100 * 1000 = 100000 nodes to load – pretty much, istn’t it? To reduce the database traffic you can first load your first 100 nodes and then, when user expands one of those, you can load its 1000 nodes. That will save considerable amount of time.