Get all child items in LINQ list

Question

I have a large backend DB, which has the following class structure that I'm using:

public class InputClass
{
    public int id { get; set; }
    public string text { get; set; }
    public string icon { get; set; }
    public int? parentId { get; set; }
}

As you can see, each element can have a parent ID, which in the end generates a tree-style list of information that the user can interact with.

Using the following sample data as an example:

var inputList = new List<InputClass>();
inputList.Add(new InputClass() { id = 1, text = "Item #1"});
inputList.Add(new InputClass() { id = 2, text = "Item #2" });
inputList.Add(new InputClass() { id = 3, text = "Item #3" });
inputList.Add(new InputClass() { id = 4, text = "SubItem #1", parentId = 1 });
inputList.Add(new InputClass() { id = 5, text = "SubItem #2", parentId = 1 });
inputList.Add(new InputClass() { id = 6, text = "SubItem #3", parentId = 2 });
inputList.Add(new InputClass() { id = 7, text = "Sub-Sub Item #1", parentId = 4 });

I would like to pass an ID # and retrieve a list of all of the elements marked with that parentID. For example, if I had the ID number of 1, the result should be as follows:

ID  Name
4   Subitem #1
5   Subitem #2
7   Sub-Sub Item #1

as you can see, the result should return everything that sits underneath id #1, including item with ID #7 (even though it has a parent ID of 4, item #4's parent is #1).

I hope the above makes sense, any ideas on how to achieve this in LINQ?

What have you tried thus far? What does your current best attempt look like? What does it return? — mech, Feb 22 '16 at 05:37
Possible duplicate of [Recursive Hierarchy - Recursive Query using Linq](http://stackoverflow.com/questions/20974248/recursive-hierarchy-recursive-query-using-linq) — danish, Feb 22 '16 at 05:40
Why it must be LinQ? You can use Recursive function this case. — NoName, Feb 22 '16 at 05:54
Sorry @Sakura, doesn't have to be Linq, can be C# too. My error in the wording of the OP — Andrew Milici, Feb 22 '16 at 05:56

Hari Prasad · Accepted Answer · 2016-02-22T06:30:59.727

5

Recursive approach.

public static IEnumerable<InputClass> Recursive(List<InputClass> items, int toplevelid)     
{
    List<InputClass> inner = new List<InputClass>();
    foreach (var t in items.Where(item=>item.parentId ==toplevelid))
    {
        inner.Add(t);
        inner = inner.Union(Recursive(items, t.id)).ToList();
    }       

    return inner;
}

Working Demo

edited Feb 22 '16 at 06:30

answered Feb 22 '16 at 05:56

Hari Prasad

16,716
4
21
35

would not not this fail if a child is created for next level ? inputList.Add(new InputClass() { id = 8, text = "Sub-Sub Item #1", parentId = 7 }); – Rangesh Feb 22 '16 at 06:09
That's true, ignored that case. Will modify accordingly. – Hari Prasad Feb 22 '16 at 06:12

NoName · Answer 2 · 2016-02-22T06:53:56.117

In this case:

static bool IsParent(IEnumerable<InputClass> lc, InputClass ic, int? ParentID)
{
    return ic.parentId != null ? ic.parentId == ParentID || IsParent(lc, lc.First(o => o.id == ic.parentId), ParentID) : false;
}

int? id = 1; // Parent ID
foreach(var i in inputList)
{
    if(IsParent(inputList, i, id)))
    {
        // get this item
    }
}

Other way:

static IEnumerable<InputClass> getAllChildren(IEnumerable<InputClass> lc, int? ParentID)
{
    foreach (var i in lc)
    {
        if (i.parentId == ParentID)
        {
            yield return i;
            foreach (var i2 in getAllChildren(lc, i.id)) yield return i2;
        }
    }
}

int? id = 1; // Parent ID
foreach (var i in getAllChildren(inputList,id))
{
    // Get this Item
}

score 2 · Answer 3 · answered Feb 22 '16 at 06:11

 static class Program
    {
        public static void Main()
        {

            IEnumerable<InputClass> allItems = someBLL.GetAllItems();

            int? someParentNode = 1;

            var allChildItems = InputClass.GetAllChildNodesRecursivrly(someParentNode, allItems);

        }
    }

    public class InputClass
    {
        public int id { get; set; }
        public string text { get; set; }
        public string icon { get; set; }
        public int? parentId { get; set; }

        public static IEnumerable<InputClass> GetAllChildNodesRecursivrly(int? ParentId,IEnumerable<InputClass> allItems)
        {
            var allChilds = allItems.Where(i => i.parentId == ParentId);

            if (allChilds==null)
            {
                return new List<InputClass>();
            }

            List<InputClass> moreChildes = new List<InputClass>();
            foreach (var item in allChilds)
            {
                moreChildes.AddRange(GetAllChildNodesRecursivrly(item.id,allItems));
            }

            return allChilds.Union(moreChildes);
        }
    }

score -2 · Answer 4 · answered Feb 22 '16 at 06:42

-2

I think that all you need to write is a lambda expression.

var results = inputList.Where(x => x.parentId == 1)

answered Feb 22 '16 at 06:42

Timothy Macharia

2,641
1
20
27

This don't take the case of multilevel child – NoName Feb 22 '16 at 06:43

Get all child items in LINQ list

4 Answers4