opening the connection with sql database

Yes, as stated by OriginalGriff,

in case of ADO.NET, we work basically in disconnected mode. So we take all the informations required for use at a time into DataSet and later manipulate there. Finally we pass the dataset to update itself with the database.

So Create a static class outside any form, and expose few methods to get DataTable/dataset or execute a query. When data is required from the database use this interface which will in turn connect to database using SqlConnection and return you the correct data.

When you want to update, send the dataset to the exposed static method, and update the same.

By this way you are not holding your connection and also update everything from a common place. We call it as DataLayer. :thumbsup:

ok..you'd always have to open and close your connections everytime you use them..but if you want to implement the write-once-run-everywhere style..then fortunately .NET come's with the ref keyword to help you..so what you can do is this..

1. create a class and put in a method for connecting to the database..example

.
.
static class DB
{
   public static void connectDB(ref SqlConnection conn, ref SqlCommand cmd)
   {
      conn = new SqlConnection();
      conn.ConnectionString="[input connection string here]";

      cmd.Connection=conn;
      cmd.CommandType=CommandType.StoredProcedure;
                           //Im assuming a stored procedure
   }
}

So all you just have to do is to call this method inside the classes you want to use it, and it will do all the above for you without you re-typing them everytime..

Example if I want to use it in a different class named useHere, I would do this..

.
.
class useHere
{
  /* First instantiate the connection and command objects because you'll just refer to them using the ref keyword */

  SqlConnection conn;
  SqlCommand cmd;

  /* Now assuming I want to add data to a table */

  public void addData(ref conn, ref cmd)
  {
     DB.connectDB(conn,cmd);
     cmd.CommandText="[input stored proc. name here]";
     conn.Open();
     cmd.ExecuteNonQuery();
     if(conn.State == ConnectionState.Open)
       {
          conn.Close();
       }

     cmd.Dispose();
  }

and you're game.. :) . If you like it, accept answer and VOTE!