Converting flat data structure into hierarchy Object using c#

You could try something like this:

1) Create a node class

class Node
{
    public int ParentId { get; private set; }
    public int Id { get; private set; }
    public string Label { get; private set; }
    public Node Parent { get; set; }
    public List<Node> Children { get; } = new List<Node>();

    public Node(int parentId, int id, string lable)
    {
        ParentId = parentId;
        Id = id;
        Label = lable;
    }

    public void AddChild(Node child)
    {
        child.Parent = this;
        Children.Add(child);
    }

    public void Trace(int indent = 1)
    {
        Enumerable.Range(0, indent).ToList().ForEach(i => Console.Write(" - "));
        Console.WriteLine(Label);
        Children.ForEach(c => c.Trace(indent + 1));
    }
}

2) Create node objects from you flat data and add them to a dictionary

var data = new List<DataRow>() {
            new DataRow { ParentId = 0, Id = 1, Label = "parent" },
            new DataRow { ParentId = 1, Id = 2, Label = "child 1" },
            new DataRow { ParentId = 1, Id = 3, Label = "child 2" },
            new DataRow { ParentId = 2, Id = 4, Label = "grand child 1" },
            new DataRow { ParentId = 2, Id = 5, Label = "grand child 2" }
        };

Dictionary<int, Node> nodes = data.ToDictionary(d => d.Id, d => new Node(d.ParentId, d.Id, d.Label));

3) Build the hierarchy by looping through all nodes calling AddChild on the parent

foreach (var node in nodes.Skip(1))
    nodes[node.Value.ParentId].AddChild(node.Value);

If you call Trace() on the top node, the output will look like this:

 - parent
 -  - child 1
 -  -  - grand child 1
 -  -  - grand child 2
 -  - child 2

Have you looked at AutoMapper?

Not sure this is what you need but it's what I use to often convert from one format to an object model.

Another alternative might be to use LINQ to query the data you have and to create the model for you.

I think you can say something like, and this is untested;

select from dataList select new {....

where new would be the new object you are creating.

However, i think maybe the brute force approach of iterating through your list might still be the way.

edit

this might help.