The "Compute" method of the DataTable class

The "Compute" method of the System.Data.DataTable class of .NET framework is a useful function for doing further calculation. Specially getting rows of data from Database or other sources and then executing further calculation in the server memories(RAM).

 public object Compute(string expression, string filter)

It Computes the given expression like SUM or Count, on the current rows with fileter if needs.The filter is to limit the rows.The "filter" is like "WHERE" portion in SQL

Example Code C#

string output = dtData.Compute("Sum(ItemQuantity)","ItemQuality ='HIGH'").ToString();

Output data in JSON format

From the server, we may need to push data to variety of clients in JSON (JavaScript Object Notation) format.As an example, the server is a web server and type of the application is a web services.The client may be a PHP/ASP Net/[XYZ...] application or Mobile app.To generate a JSON data from Data, we can use the "JavaScriptSerializer" method from the library of  "System.Web.Script.Serialization" of .NET framework.Here is the code example.

C#
===
using System;
using System.Collections.Generic;
using System.Web.Script.Serialization;
using System.Data;
using System.Text;
namespace TESTConsoleApplicatio
{
    public class JSONCLASS
    {
        public static string GetJSONData(DataTable dt)
        {
        
          StringBuilder sb = new StringBuilder();
        
          List> result = new List>();
       
          foreach (DataRow dr in dt.Rows)
          {
              Dictionary drow = new Dictionary();
              for (int i = 0; i < dt.Columns.Count; i++)
              {
               
                  drow.Add(dt.Columns[i].ColumnName, dr[i]);
              }
              result.Add(drow);
          }


          JavaScriptSerializer js = new JavaScriptSerializer();  
          string jsonString = js.Serialize(result);
            //OUTPUT JSON
            //{"product":[{\"ID\":1001,\"name\":\"Book 1\",\"category\":\"Category 1\"},
            //             {\"ID\":2001,\"name\":\"Book 2\",\"category\":\"Category 2\"},
            //              {\"ID\":1002,\"name\":\"Book 22\",\"category\":\"Category 1\"} ]}     

          return "{\""  + dt.TableName + "\":" + jsonString + "}";

        }

    }
}

========
INPUT/OUTPUT

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;

namespace TESTConsoleApplicatio
{
    class Program
    {
        static void Main(string[] args)
        {
             //INPUT DATA.May be we can get data from database or other sources
 
            DataTable dt = new DataTable("product");
            dt.Columns.Add("ID",typeof( int));                     
            dt.Columns.Add("name");
            dt.Columns.Add("category");

            DataRow rw = dt.NewRow();
            rw["ID"] = 1001;
            rw["name"] = "Book 1";
            rw["category"] = "Category 1";
            dt.Rows.Add(rw);
               
                 rw = dt.NewRow();
                rw["ID"] = 2001;
                rw["name"] = "Book 2";
                rw["category"] = "Category 2";
                dt.Rows.Add(rw);

             rw = dt.NewRow();
                rw["ID"] = 1002;
                rw["name"] = "Book 22";
                rw["category"] = "Category 1";
                dt.Rows.Add(rw);

           

            string jsonOutput = JSONCLASS.GetJSONData(dt);
            
               //We can out put data as a web services
            Console.Write(jsonOutput);
            Console.ReadLine();
         
           
           
           
               
           
        }
    }
}