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"
  }
}

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