// ObjectDB for Java Demo - JDO Directory - A Brief JDO Tutorial
// Copyright (C) 2001-2003, ObjectDB Software. All rights reserved.
package directory.step3;
import java.util.*;
import javax.jdo.*;
import directory.pc.*;
/**
* The Retrieve class shows how to use JDOQL queries to retrieve objects,
* and how to use extents to iterate over persistent objects.
*/
public class Retrieve {
/**
* Runs the example.
*/
public void run() {
// Obtain a PersistenceManager instance:
PersistenceManager pm =
directory.Utilities.getPersistenceManager(false);
// Use Extents and Queries:
try {
printAll(Category.class, pm);
printAll(Item.class, pm);
executeQuery1(pm);
executeQuery2(pm);
executeQuery3(pm);
executeQuery4(pm);
}
catch (RuntimeException x) {
System.out.println("Error: " + x.getMessage());
}
// Close the PersistenceManager instance:
finally {
if (pm.currentTransaction().isActive())
pm.currentTransaction().rollback();
if (!pm.isClosed())
pm.close();
}
}
/**
* Prints all the instances of a specified class.
*/
private static void printAll(Class cls, PersistenceManager pm) {
Extent extent = pm.getExtent(cls, true);
Iterator itr = extent.iterator();
printCollection("All " + cls.getName() + " instances:", itr);
extent.close(itr);
}
/**
* Prints a collection content using a specified iterator.
*/
private static void printCollection(String title, Iterator itr) {
System.out.println(title);
while (itr.hasNext())
System.out.println(" " + itr.next());
}
/**
* Retrieves all the books with more than 300 pages.
*/
private void executeQuery1(PersistenceManager pm) {
Query query = pm.newQuery(Book.class, "pages > 300");
Collection results = (Collection)query.execute();
printCollection("Books with more than 300 pages:", results.iterator());
query.closeAll();
}
/**
* Retrieves all the items in small categories.
*/
private static void executeQuery2(PersistenceManager pm) {
Query query = pm.newQuery(Item.class, "parent.elements.size() <= size");
query.declareParameters("int size");
Collection results = (Collection)query.execute(new Integer(3));
printCollection("Items in small categories:", results.iterator());
query.closeAll();
}
/**
* Retrieves all the books published in 2002.
*/
private static void executeQuery3(PersistenceManager pm) {
Query query = pm.newQuery(Book.class);
query.setFilter("date >= fromDate && date <= toDate");
query.declareImports("import java.util.Date");
query.declareParameters("Date fromDate, Date toDate");
query.setOrdering("date descending"); // order from new to old
Collection results =
(Collection)query.execute(getYearDate(2002), getYearDate(2003));
printCollection("Books published in 2002:", results.iterator());
query.closeAll();
}
/**
* Returns a Date representing the first moment of a specified year.
*/
private static Date getYearDate(int year) {
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.set(Calendar.YEAR, year);
return calendar.getTime();
}
/**
* Retrieves all the categories containing an item with a short name.
*/
private static void executeQuery4(PersistenceManager pm) {
Query query = pm.newQuery(Category.class);
query.declareParameters("int length");
query.declareVariables("Item item");
query.setFilter(
"elements.contains(item) && item.name.length() <= length");
Collection results = (Collection)query.execute(new Integer(10));
printCollection("Categories containing an item with a short name: ",
results.iterator());
query.closeAll();
}
}
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