convert from SqlDataReader to JSON

Question

public string toJSON(SqlDataReader o)
{
    StringBuilder s = new StringBuilder();
    s.Append(\"[\");
    if (o.HasRows)
        while (o.Read())
            s.App         


        

Answer 1

I encounter use cases where the number of rows being returned by the data reader may become problematic with respect to memory consumption. The following code uses a JsonWriter (from JSON.NET) over a stream. One can certainly debate the utility of enormous JSON documents, but sometimes our use cases are dictated by others :-)

A few notes:

• My SqlDataReader may contain multiple result sets ('tables')
• I may be sending the output to a FileStream or an HttpResponse stream
• I've 'abstracted' my object names to match the first column returned per result set
• Because of the potential for large result sets, I use async methods of the SqlDataReader.
• I'm letting JSON.NET handle all the serialization issue of the actual data contained in the data reader results.

The code:

var stream = ... // In my case, a FileStream or HttpResponse stream
using (var writer = new JsonTextWriter(new StreamWriter(stream)))
{
    writer.WriteStartObject();  
    do
    {
        int row = 0;
        string firstColumn = null;
        while (await reader.ReadAsync())
        {
            if (row++ == 0)
            {
                firstColumn = reader.GetName(0);
                writer.WritePropertyName(string.Format("{0}Collection", firstColumn));
                writer.WriteStartArray();   
            }
            writer.WriteStartObject();
            for (int i = 0; i < reader.FieldCount; i++)
            {
                if (!reader.IsDBNull(i)) { 
                    writer.WritePropertyName(reader.GetName(i));
                    writer.WriteValue(reader.GetValue(i));
                }
            }
            writer.WriteEndObject(); 
        }
        writer.WriteEndArray();
    } while (await reader.NextResultAsync());

    writer.WriteEndObject();
}

An example of heterogeneous output would be:

{
    "ContactCollection": {
        "ContactItem": [{
                "ContactID": "1",
                "Contact": "Testing",
            },
            {
                "ContactID": "2",
                "Contact": "Smith, John",
            },
            {
                "ContactID": "4",
                "Contact": "Smith, Jane",
            }
        ],
        "MessageItem": [{
                "MessageID": "56563",
                "Message": "Contract Review Changed",
            },
            {
                "MessageID": "56564",
                "Message": " Changed",
            },
            {
                "MessageID": "56565",
                "Message": "Contract Review - Estimated Completion Added.",
            }
        ]
    }
}

Reference:

• http://www.newtonsoft.com/json/help/html/Performance.htm