Convert DataTable to JSON with key per row

This is quite simple with JSON.NET. Just convert your data table into the equivalent dictionary of dictionaries:

public Dictionary<string, Dictionary<string, object>> DatatableToDictionary(DataTable dt, string id){    var cols = dt.Columns.Cast<DataColumn>().Where(c => c.ColumnName != id);    return dt.Rows.Cast<DataRow>()             .ToDictionary(r => r[id].ToString(),                            r => cols.ToDictionary(c => c.ColumnName, c => r[c.ColumnName]));}

Then call:

JsonConvert.SerializeObject(DatatableToDictionary(dt, "ID"), Newtonsoft.Json.Formatting.Indented);

Here's the full test:

var dt = new DataTable("MyTable");dt.Columns.Add("ID");dt.Columns.Add("Name");dt.Columns.Add("Active");dt.LoadDataRow(new[] {"ID1", "John", "True"}, true);dt.LoadDataRow(new[] {"ID2", "Bill", "False"}, true);JsonConvert.SerializeObject(DatatableToDictionary(dt, "ID"));

And the result:

{  "ID1": {    "Name": "John",    "Active": "True"  },  "ID2": {    "Name": "Bill",    "Active": "False"  }}

Using JSON.NET (Newtonsoft.Json.Linq)

var obj = new JObject(    dataTable.Rows.Cast<DataRow>()         .Select(r => new JProperty(r["ID"].ToString(),                 new JObject(                     new JProperty("Name", r["Name"].ToString()),                     new JProperty("Active", r["Active"].ToString())                 )             )));// Convert the JObject to a JSON stringvar json = obj.ToString();