Linq to build hierarchical list

Question

I have a method that retrieves a set of records from a database.

I map this data to a business object - let's call the business object ProcessModel. One of the properties in ProcessModel is a list, called ProcessChildren. The property is List.

So, the data is linked by various fields/properties. There is one object at the top of the hierarchical list, then that object has multiple objects in it's ProcessChildren property, those objects have multiple objects in their ProcessChildren properties etc.

Anyway, I wrote quite a bit of code to iterate through the dataset returned, and build the hierarchical list, which I then bind to a TreeView in Silverlight.

I would be very appreciative if someone could provide me with a much cleaner, simpler way to do this, either using linq, or using linq or some other approach via means of an extension method.

I have included the code that I am currently using, to hopefully better illustrate what I am trying to achieve.

var processes = new List<Process>();

        var rootLevelProcesses = new List<Process>();

        var allProcesses = new List<Process>();

        foreach (Process process in e.Results)
        {
            process.ProcessChildren = new List<Process>();

            if (process.ParentId > 0 || (process.ParentId == 0 && process.EntityId == 1))
            {
                allProcesses.Add(process);
            }
        }

        var rootProcess =
                    (from parent in e.Results
                     where parent.EntityType == 1 && parent.ContainerLevel <= 1
                     select parent).FirstOrDefault();

        processes.Add(rootProcess);

        var level2Processes = (from parent in allProcesses
                               where parent.EntityType == 1 && parent.ContainerLevel == 2
                               select parent).ToList();

        foreach (Process process in level2Processes)
        {
            var level3Processes = (from parent in allProcesses
                                   where parent.EntityType == 1 && parent.ContainerLevel == 3
                                   select parent).ToList();

            process.ProcessChildren = level3Processes;
        }

        processes[0].ProcessChildren = level2Processes;

        foreach (Process process in processes)
        {
            if (process.ProcessChildren != null && process.ProcessChildren.Count > 0)
            {
                foreach (Process level1 in process.ProcessChildren)
                {
                    if (level1.EntityType == 1)
                    {
                        var children =
                        (from child in allProcesses
                         where child.ParentId == level1.EntityId
                         select child).ToList();

                        level1.ProcessChildren = children;

                        foreach (Process level2 in level1.ProcessChildren)
                        {
                            if (level2.EntityType == 1)
                            {
                                children =
                            (from child in allProcesses
                             where child.ParentId == level2.EntityId
                             select child).ToList();

                                level2.ProcessChildren = children;

                                foreach (Process level3 in level2.ProcessChildren)
                                {
                                    if (level3.EntityType == 1)
                                    {
                                        children =
                                    (from child in allProcesses
                                     where child.ParentId == level3.EntityId
                                     select child).ToList();

                                        level3.ProcessChildren = children;
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }

Answer 1

This related post might help....

Update: here's code in support of comments below... You will need to edit to support your own classes.

public class Proc
{
    public System.Diagnostics.Process RealProc;
    public List<Proc> SubProcs = null;
}

void Main()
{
    var Processes = from p in System.Diagnostics.Process.GetProcesses() select new Proc { RealProc = p, SubProcs = null };
    while (Processes.Any(pr => pr.SubProcs == null))
    {
        foreach(Proc pr in Processes)
        {
            pr.RealProc.Id.Dump();
            pr.SubProcs = Processes.Where(prx => prx.RealProc.ParentId == pr.Id).ToList();  // doesn't work because no ParentId
        }
    }
}