Build JSON Hierarchy from Structured Data

One way to turn a flat table into a hierarchy is to put all your nodes into a dictionary. Then iterate over the dictionary, and for each node, look up its parent and add it to the parent's children. From there, you just need to find the root and serialize it.

Here is an example program to demonstrate the approach:

class Program{    static void Main(string[] args)    {        IEnumerable<Location> locations = new List<Location>        {            new Location { Id = 1, ParentId = 1, Name = "TopLoc" },            new Location { Id = 2, ParentId = 1, Name = "Loc1" },            new Location { Id = 3, ParentId = 1, Name = "Loc2" },            new Location { Id = 4, ParentId = 2, Name = "Loc1A" },        };        Dictionary<int, Location> dict = locations.ToDictionary(loc => loc.Id);        foreach (Location loc in dict.Values)        {            if (loc.ParentId != loc.Id)            {                Location parent = dict[loc.ParentId];                parent.Children.Add(loc);            }        }        Location root = dict.Values.First(loc => loc.ParentId == loc.Id);        JsonSerializerSettings settings = new JsonSerializerSettings        {            ContractResolver = new CamelCasePropertyNamesContractResolver(),            Formatting = Formatting.Indented        };        string json = JsonConvert.SerializeObject(root, settings);        Console.WriteLine(json);    }}class Location{    public Location()    {        Children = new List<Location>();    }    public int Id { get; set; }    public int ParentId { get; set; }    public string Name { get; set; }    public List<Location> Children { get; set; }}

Here is the output:

{  "id": 1,  "parentId": 1,  "name": "TopLoc",  "children": [    {      "id": 2,      "parentId": 1,      "name": "Loc1",      "children": [        {          "id": 4,          "parentId": 2,          "name": "Loc1A",          "children": []        }      ]    },    {      "id": 3,      "parentId": 1,      "name": "Loc2",      "children": []    }  ]}