illustrates how to specify and use a relationship between two DataTable objects : DataTable « Database ADO.net « C# / C Sharp

1. C# / C Sharp
2. Database ADO.net
3. DataTable

illustrates how to specify and use a relationship between two DataTable objects

 
/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy

Publisher: Sybex;
ISBN: 0782129110
*/

/*
  Example23_6.cs illustrates how to specify and use a
  relationship between two DataTable objects
*/

using System;
using System.Data;
using System.Data.SqlClient;

public class Example23_6
{

  public static void Main()
  {

    // formulate a string containing the details of the
    // database connection
    string connectionString =
      "server=localhost;database=Northwind;uid=sa;pwd=sa";

    // create a SqlConnection object to connect to the
    // database, passing the connection string to the constructor
    SqlConnection mySqlConnection =
      new SqlConnection(connectionString);

    // formulate a string containing a SELECT statement to
    // retrieve a row from the Customers table
    string selectString =
      "SELECT CustomerID, CompanyName " +
      "FROM Customers " +
      "WHERE CustomerID = 'ALFKI'";

    // create a SqlCommand object to hold the SELECT statement
    SqlCommand mySqlCommand = mySqlConnection.CreateCommand();

    // set the CommandText property of the SqlCommand object to
    // the SELECT string
    mySqlCommand.CommandText = selectString;

    // create a SqlDataAdapter object
    SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();

    // set the SelectCommand property of the SqlAdapter object
    // to the SqlCommand object
    mySqlDataAdapter.SelectCommand = mySqlCommand;

    // create a DataSet object to store the results of
    // the SELECT statement
    DataSet myDataSet = new DataSet();

    // open the database connection using the
    // Open() method of the SqlConnection object
    mySqlConnection.Open();

    // use the Fill() method of the SqlDataAdapter object to
    // retrieve the rows from the database, storing the rows
    // in a DataTable named "Customers"
    mySqlDataAdapter.Fill(myDataSet, "Customers");

    // formulate a string containing a SELECT statement to
    // retrieve the rows from the Orders table where the CustomerID
    // column is equal to ALFKI
    selectString =
      "SELECT OrderID, CustomerID " +
      "FROM Orders " +
      "WHERE CustomerID = 'ALFKI'";

    // set the CommandText property of the SqlCommand object to
    // the SELECT string
    mySqlCommand.CommandText = selectString;

    // use the Fill() method of the SqlDataAdapter object to
    // retrieve the rows from the database, storing the rows
    // in a DataTable named "Orders"
    mySqlDataAdapter.Fill(myDataSet, "Orders");

    // use the Add() method through the Relations property
    // to define a relationship between the Customers and
    // Orders DataTable objects
    myDataSet.Relations.Add(
      "Orders",
      myDataSet.Tables["Customers"].Columns["CustomerID"],
      myDataSet.Tables["Orders"].Columns["CustomerID"]
    );

    // display the rows in the Customers and Orders DataTable objects,
    // using the GetChildRows() method to get the orders for the
    // customer
    DataTable customers = myDataSet.Tables["Customers"];
    foreach (DataRow customer in customers.Rows)
    {
      Console.WriteLine("CustomerID = " + customer["CustomerID"]);
      Console.WriteLine("CompanyName = " + customer["CompanyName"]);

      DataRow[] orders = customer.GetChildRows("Orders");
      Console.WriteLine("This customer placed the following orders:");
      foreach (DataRow order in orders)
      {
        Console.WriteLine("  OrderID = " + order["OrderID"]);
      }

    }

    // close the database connection using the Close() method
    // of the SqlConnection object
    mySqlConnection.Close();

  }

}


           
         
  

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