Receiving Results from a Remote Database

This example uses the handle_results callback function, which processes results from the remote database and sends them to the client.

1. Define the function and the function parameters for handle_results:

   int handle_results (rmtproc, srvproc)
   DBPROCESS   FAR * rmtproc;    // DBPROCESS handle          
                                 // to the remote database    
   SRV_PROC    FAR * srvproc;    // Process handle to send    
                                 // results to the client     
   
   {
       short    cols;            // Data columns returned     
       int      i;               // Index variable            
       DBINT    rows;            // Number of rows sent       
       BOOL     results_sent;    // Number of results sets sent  
       BOOL     gotcompute;      // COMPUTE row indicator     
       short *  paramarray;      // Return parameters         
       RETCODE  returnvalue;     // Value returned from       
                                 // DB-Library calls          
   

2. Use the DB-Library dbresults callback function to loop through each results set. Since a command can consist of multiple commands or a single command that has multiple results sets, use a WHILE loop to process each results set:

   // Process the results from the remote database.   
   
   while (TRUE)
   {
          returnvalue = dbresults (rmtproc);
          if (returnvalue == NO_MORE_RESULTS)
              break;
   }
   

3. Get the number of data columns in the row using the DB-Library dbnumcols function, and describe each column in the row using the srv_describe function:

   cols = dbnumcols (rmtproc); // How many data columns             
                               // are in the row?                   
   for (i = 1; i <= cols; i+) // Call srv_describe for each column 
   
   {
        srv_describe (srvproc,
                      i,
                      dbcolname (rmtproc, i),
                      SRV_NULLTERM,
                      (DBINT)dbcolntype (rmtproc, i),
                      dbcollen (rmtproc, i),
                      (DBINT)dbcolntype (rmtproc, i),
                      dbcollen (rmtproc, i),
                      (BYTE *)NULL);
   }
   

   You may also need to use srv_setutype to set the user-defined datatype information for a column. For more information, see the GATEWAY sample application.

4. Set the address of the column data using srv_setcoldata and the length of the column data using srv_setcollen. Move the row from the remote database to the client using the srv_sendrow function:

   rows = 0;  // Initialize a counter for the row number.
   while (TRUE)
   
   {
          returnvalue = dbnextrow (rmtproc);
          if (returnvalue == NO_MORE_ROWS)   // No more rows so exit  
                                             // loop, set the DONE    
                                             // status, and exit.     
               break;
   
          // Move the row from the remote database to the client.     
   
          for (i = 1; i <= cols; i+)
   
          { 
               srv_setcollen (srvproc, i,
                    (short)dbdatlen (rmtproc, i));
               srv_setcoldata (srvproc, i, dbdata(rmtproc, i));
           }
   
           // Send the row to the client.     
   
          if (srv_sendrow (srvproc) == SUCCEED)
              rows+;                        // Go to the next row. 
   }
   

5. Determine if the count value in the remote database is relevant and, if so, pass it to the client. Send a completion message for the current results set:

   if (dbnumcols (rmtproc) > 0)
       rows = DBCOUNT(rmtproc)  0L ? 0L: rows;
   else
   {
       rows = DBCOUNT (rmtproc);
   
      // Now set the flag so a completion message is sent for the  
      // current results set.                                      
      results_sent = TRUE;
   
   }
   
   // Send the final done packet for the execution of the command  
   // batch. The previous batch was one that might have returned   
   // rows, so set the DONE status accordingly.                    
   if (rows > 0)
       srv_senddone (srvproc,
                 SRV_DONE_COUNT | SRV_DONE_FINAL,
                 (DBUSMALLINT) 0,
                 rows);
   else 
       srv_senddone (srvproc,
                 SRV_DONE_FINAL,
                 (DBUSMALLINT) 0,
                 (DBINT) 0);
   

6. Once a set of results has been retrieved from the remote database, a completion message must be sent to the client for the last results set retrieved. This must be done before another set of results can be obtained.

   // If this is the second time through the loop, send a completion 
   // message to the client for the previous results set sent.       
       if (results_sent == TRUE)
         {  // If the previous batch returned rows, set              
            // the DONE status accordingly.                          
            if (rows > 0)
                 srv_senddone (srvproc,
                           SRV_DONE_MORE | SRV_DONE_COUNT,
                           (DBUSMALLINT)0,
                           rows);
            else
                 srv_senddone (srvproc,
                           SRV_DONE_MORE,
                           (DBUSMALLINT)0,
                           (DBINT) 0);
            }