Examples of org.apache.empire.db.DBReader

org.apache.empire.db.DBReader
This class is used to perform database queries from a DBCommand object and access the results.
In oder to perform a query call the open() function or - for single row queries - call getRecordData();
You can iterate through the rows using moveNext() or an iterator.

However take care: A reader must always be explicitly closed using the close() method!
Otherwise you may lock the JDBC connection and run out of resources.
Use
```
try { ... } finally { reader.close(); } 
```
to make sure the reader is closed.

To access and work with the query result you can do one of the following:
- access field values directly by using one of the get... functions (see {@link DBRecordData})
- get the rows as a list of Java Beans using by using {@link DBReader#getBeanList(Class,int)}
- get the rows as an XML-Document using {@link DBReader#getXmlDocument()}
- initialize a DBRecord with the current row data using {@link DBReader#initRecord(DBRowSet,DBRecord)}
  This will allow you to modify and update the data.

        cmd.select(T_EMP.getColumns());
        // Set Constraints
        cmd.where(T_EMP.C_RETIRED.is(false));


        // Query Records and print output
        DBReader reader = new DBReader();
        try
        {
            // Open Reader
            System.out.println("Running Query:");
            System.out.println(cmd.getSelect());
            reader.open(cmd, conn);
            // Print output
            DBRecord record = new DBRecord();
            while (reader.moveNext())
            {
                // Calculate sum
                int sum = 0;
                for (int i=0; i<reader.getFieldCount(); i++)
                    sum += calcCharSum(reader.getString(i));
                // Init updateable record
                reader.initRecord(EMP, record);
                // reader
                record.setValue(T_EMP.C_CHECKSUM, sum);
                record.update(conn);
            }
            // Done
            db.commit(conn);


        } finally
        {
            // always close Reader
            reader.close();
        }
    }

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        cmd.select(T_EMP.getColumns());
        // Set Constraints
        cmd.where(T_EMP.C_RETIRED.is(false));


        // Query Records and print output
        DBReader reader = new DBReader();
        try
        {   // Open Reader
            System.out.println("Running Query:");
            System.out.println(cmd.getSelect());
            reader.open(cmd, conn);
            // Print output
            HashMap<Integer, DBRecord> employeeMap = new HashMap<Integer, DBRecord>();
            while (reader.moveNext())
            {
                DBRecord rec = new DBRecord();
                reader.initRecord(T_EMP, rec);
                employeeMap.put(reader.getInt(T_EMP.C_EMPLOYEE_ID), rec);
            }
            return employeeMap;


        } finally
        {   // always close Reader
            reader.close();
        }
    }

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     * @param conn the connection
     */
    private static void printQueryResults(DBCommand cmd, Connection conn)
    {
        // Query Records and print output
        DBReader reader = new DBReader();
        try
        {   // Open Reader
            System.out.println("Running Query:");
            System.out.println(cmd.getSelect());
            reader.open(cmd, conn);
            // Print column titles 
            System.out.println("---------------------------------");
            int count = reader.getFieldCount();
            for (int i=0; i<count; i++)
            {   // Print all column names
                DBColumnExpr c = reader.getColumnExpr(i);
                if (i>0)
                    System.out.print("\t");
                System.out.print(c.getName());
            }
            // Print output
            System.out.println("");
            // Text-Output by iterating through all records.
            while (reader.moveNext())
            {
                for (int i=0; i<count; i++)
                {   // Print all field values
                    if (i>0)
                        System.out.print("\t");
                    // Check if conversion is necessary
                    DBColumnExpr c = reader.getColumnExpr(i);
                    Options opt = c.getOptions();
                    if (opt!=null)
                    {   // Option Lookup
                        System.out.print(opt.get(reader.getValue(i)));
                    }
                    else
                    {   // Print String
                        System.out.print(reader.getString(i));
                    }
                }
                System.out.println("");
            }


        } finally
        {   // always close Reader
            reader.close();
        }
    }

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