Question

I have a table like this (Groups):

ID       Name           ParentID
1        Group 1        null
2        Group 2        null
3        SubGr 1-1      1
4        SubGr 1-2      1
5        SubGr 2-1      2
6        Group 3        null
7        SubGr 1-2-1    4
..... and so on

I want to serialize this to JSON looking like this:

[{"id":1,
  "name":"Group 1",
  "children": [
    {
     "id":3,
     "name":"SubGr 1-1",
     "children":null
    },{
     "id":4,
     "name":"SubGr 1-2",
     "children": [
       {
        "id":7,
        "name":"SubGr 1-2-1", 
        "children": null
       }
      ]
    }
   ]
  },
 {"id":2,
  "name":"Group 2",
  "children": [
    {
     "id":5,
     "name":"SubGr 2-1",
     "children":null
    }
   ]
 },
 {"id":6,
  "name": "Group 3",
  "children": null
 }
]

As you can see, you can have indefinite subgroups.

How can I make such a query in LINQ and output it in JSON like the example above?

I have no problem outputting the JSON as seperated elements, with ParentID, but I need to have the structure as mentioned above.

This is the code that I am currently working with, after trying different things around, but with no luck still (this version only gives two levels):

    public ActionResult GetGroups()
    {
        var groupobjs = db.GroupObjs.ToList();

        var items = groupobjs.Where(p => p.ParentID == null).Select(p => new
        {
            id = p.ID,
            name = p.Name,
            children = groupobjs.Where(c => c.ParentID == p.ID).Select(c => new {
                id = c.ID,
                name = c.Name
            })
        });



        return Json(items, JsonRequestBehavior.AllowGet);
    }      

Answer 1

I was working on some code similar to what @Hunter-974 recommended.

public class Group
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int? ParentId { get; set; }
    public List<Group> Subgroups { get; set; }

    public Group()
    {
        this.Subgroups = new List<Group>();
    }
}

class Program
{
    static void Main()
    {
        Group[] groups = new Group[]
        {
            new Group { Id = 1, Name = "Group 1", ParentId = null },
            new Group { Id = 2, Name = "Group 2", ParentId = null },
            new Group { Id = 3, Name = "SubGr 1-1", ParentId = 1 },
            new Group { Id = 4, Name = "SubGr 1-2", ParentId = 1 },
            new Group { Id = 5, Name = "SubGr 2-1", ParentId = 2 },
            new Group { Id = 6, Name = "Group 3", ParentId = null },
            new Group { Id = 7, Name = "SubGr 1-2-1", ParentId = 4 }
        };

        foreach (Group g in groups)
            if (g.ParentId.HasValue)
                groups.Single(group => group.Id == g.ParentId.Value).Subgroups.Add(g);

        var rootgroups = groups.Where(g => g.ParentId == null);

        JavaScriptSerializer js = new JavaScriptSerializer();
        Console.WriteLine(js.Serialize(rootgroups));
    }
}