Examples of com.google.appengine.api.datastore.Query.reverse()

com.google.appengine.api.datastore.Query.reverse()

Creates a query sorted in the exact opposite direction as the current one. This function requires a sort order on {@link Entity#KEY_RESERVED_PROPERTY}to guarantee that each entity is uniquely identified by the set of properties used in the sort (which is required to exactly reverse the order of a query). Advanced users can reverse the sort orders manually if they know the set of sorted properties meets this requirement without a order on {@link Entity#KEY_RESERVED_PROPERTY}. The results of the reverse query will be the same as the results of the forward query but in reverse direction. {@link Cursor Cursors} from the original query can be converted for use withthe reverse query through {@link Cursor#reverse()}. @return A new query with the sort order reversed. @throws IllegalStateException if the current query is not sorted by{@link Entity#KEY_RESERVED_PROPERTY}.

        QueryResultIterator<Entity> iter = service.prepare(query).asQueryResultIterator();
        Entity e1 = iter.next();
        Entity e2 = iter.next();
        Cursor cursor = iter.getCursor();
        //reverse
        query = query.reverse();
        cursor = cursor.reverse();
        iter = service.prepare(query).asQueryResultIterator(FetchOptions.Builder.withStartCursor(cursor));
        Assert.assertEquals(e2, iter.next());
        Assert.assertEquals(e1, iter.next());
    }

        final Query query = new Query(kindName, rootKey);
        query.addSort(Entity.KEY_RESERVED_PROPERTY);
        query.addSort("intData");


        List<Entity> list1 = service.prepare(query).asList(FetchOptions.Builder.withDefaults());
        List<Entity> list2 = service.prepare(query.reverse()).asList(FetchOptions.Builder.withDefaults());


        int size = list1.size();
        Assert.assertEquals(size, list2.size());
        for (int i = 0; i < size; i++) {
            Assert.assertEquals(list1.get(i), list2.get(size - i - 1));

All source code are property of their respective owners. Java is a trademark of Sun Microsystems, Inc and owned by ORACLE Inc. Contact coftware#gmail.com.