Recursive linq query to get parent list or child list from the given id

Question

I have one list of records having parent child relation. As per the below example if we start from 5 which is having lowest sort order the squence will be 5,7,4,3,1,6,2

Now if I pass 3 I want parentId list that is 4,7,5 and childId list that is 1,6,2 I am able to achieve this by recursive function as per below method. Can somone help me to achive this by linq query rather than recursive method.

  public class ParentChildClass
        {
            public int Id { get; set; }
            public int? ChildId { get; set; }
            public int SortOrder { get; set; }

        }
    List<ParentChildClass>  parentChildList = new List<ParentChildClass>();
            public  void CreateParentChildList()
            {            
                parentChildList.Add(new ParentChildClass() { Id = 1, ChildId = 6 , SortOrder = 100});
                parentChildList.Add(new ParentChildClass() { Id = 2, ChildId = null, SortOrder = 100 });
                parentChildList.Add(new ParentChildClass() { Id = 3, ChildId = 1 , SortOrder = 100 });
                parentChildList.Add(new ParentChildClass() { Id = 4, ChildId = 3 , SortOrder = 100 });
                parentChildList.Add(new ParentChildClass() { Id = 5, ChildId = 7 , SortOrder = 10 });
                parentChildList.Add(new ParentChildClass() { Id = 6, ChildId = 2 , SortOrder = 100 });
                parentChildList.Add(new ParentChildClass() { Id = 7, ChildId = 4 , SortOrder = 100 });            
            }

public List<int> GetRecursiveParentIds (int parentId,List<int> parentIds)
        {
            CreateParentChildList();
            var parent = parentChildList.FirstOrDefault(i => i.ChildId == parentId);
            if (parent != null)
            {
                if (parentIds == null || !parentIds.Any())
                {
                    parentIds = new List<int>();
                }

                if (parent.ChildId != null)
                {
                    parentIds.Add((int)parent.Id);
                    GetRecursiveParentIds((int)parent.Id, parentIds);
                }
            }
            return parentIds;
        }

 public List<int> GetRecursiveChildIds(int childId, List<int> childIds)
        {
            CreateParentChildList();
            var child = parentChildList.FirstOrDefault(i => i.Id == childId);
            if (child != null)
            {
                if (childIds == null || !childIds.Any())
                {
                    childIds = new List<int>();
                }

                if (child.ChildId != null)
                {
                    childIds.Add((int)child.ChildId);
                    GetRecursiveChildIds((int)child.ChildId, childIds);
                }
            }
            return childIds;
        }

Thanks

Does https://stackoverflow.com/questions/4814242/linq-recursion-function answer your question? — Athanasios Kataras, Dec 26 '19 at 08:14
LINQ doesn't support recursion. So what you ask (LINQ-only) simply can't be done. — Gert Arnold, Dec 26 '19 at 21:39

score 0 · Answer 1 · answered Dec 26 '19 at 11:26

You can try the below,

     public List<int> GetOrder() {
        CreateParentChildList();
        var tail = parentChildList.First(x => x.ChildId == null);
        int id = tail.Id;
        List<int> res = new List<int>() { tail.Id };
        while(true){
            var temp = parentChildList.FirstOrDefault(x => x.ChildId == id);
            if (temp == null)
                break;
            res.Add(temp.Id);
            id = temp.Id;
        }
        return res;
    }

    public List<int> GetRecursiveParentIds(int id) {
        var order = GetOrder();
        order.Reverse();
        var res = order.TakeWhile(x => x != id);
        res = res.Reverse();
        return res.ToList();
    }

    public List<int> GetRecursiveChildIds(int id) {
        var order = GetOrder().TakeWhile(x => x != id);
        var res = order.Reverse();
        return res.ToList();
    }

GetRecursiveChildIds(3) returns 1,6,2

GetRecursiveParentIds(3) returns 4,7,5

Recursive linq query to get parent list or child list from the given id

1 Answers1