Writing a Provider That Handles Queries

The following example provider program uses the query APIs to parse the WQL string that was passed to the provider by the execQuery method. This program parses the select expression in the query string, performs a deep enumeration of the class, and iterates through the instances in the enumeration, matching the query expression and select list to each instance. Finally, the program returns a vector containing the enumeration of the instances that match the query string.

Example 5–1 Provider That Handles Queries

/*
 * The execQuery method will support only limited queries 
 * based upon partial key matching. An empty Vector is 
 * returned if no entries are selected by the query.
 *
 * @param  op The CIM object path of the CIM instance to be returned
 * @param  query The CIM query expression
 * @param  ql The CIM query language indicator
 * @param  cc The CIM class reference
 *
 * @return  A vector of CIM object instances
 *
 * @version    1.19 01/26/00
 * @author     Sun Microsystems, Inc.
 */
public CIMInstance[] execQuery(CIMObjectPath op, 
                       String query, 
                       String  ql,
                       CIMClass cc) 
           throws CIMException {

   Vector result = new Vector();
   try {
       SelectExp q = new SelectExp(query);
       SelectList attrs = q.getSelectList();
       NonJoinExp from = (NonJoinExp)q.getFromClause();
       QueryExp where = q.getWhereClause();

       CIMInstance[] v = enumerateInstances(op, false, true, 
                                            true, null, cc);

       // filtering the instances
       for (int i = 0; i < v.length; i++) {
               if ((where == null) || (where.apply(v[i]) == true)) {
                   result.addElement(attrs.apply(v[i]));
                } 
       }
   } catch (Exception e) {
       throw new CIMException(CIMException.CIM_ERR_FAILED, e.toString());
   }
   return (CIMInstance[])result.toArray();
 } // execQuery
}