Executing Queries

There are several ways to process the results of a query.

Whenever one of the following methods to process the query’s results is called, the query will be executed automatically.

All touched entities will be loaded on demand during the process.

The GigaMap employs internal read-write locking, which makes it effectively thread-safe.

However, to determine when the read-locks should be released, all query iteration resources must be closed after use.

The default iterator closes automatically once fully traversed. Everything else must be closed manually.

All resources implement AutoCloseable, making them best suited for use in a try-with-resources block.

Iterators

GigaQuery extends Iterable, so all the usual options are available.

GigaQuery<Person> query = gigaMap.query(...);

/*
 * Not recommended
 * because if the loop exits before the iterator is finished,
 * the iterator will stay open.
 */
for(Person person : query)
{
    // do something
}

/*
 * Always use try-with-resources,
 * just to make sure that the iterator is closed eventually.
 */
try(GigaIterator<Person> iterator = query.iterator())
{
    while(iterator.hasNext())
    {
        Person person = iterator.next();
    }
}

// Internal iteration works as well.
try(GigaIterator<Person> iterator = query.iterator())
{
	iterator.forEachRemaining(person -> ...);
}

Streams

Java’s powerful Streams API offers a lot of methods for further filtering, mapping, aggregating, and collecting after the query is executed.

Be aware that the stream does not influence the query but is executed afterward.

try(Stream<Person> stream = query.stream())
{
    // ...
}

Collectors

The most convenient way to get the results of a query is through collectors. There’s no need to worry about closing the resource; it is handled internally.

GigaQuery<Person> query = gigaMap.query(...);

// get the complete result as a list
List<Person> list = query.toList();

// limit the result to 100 entities
List<Person> list = query.toList(100);

// get the third page with 100 entities
List<Person> list = query.toList(
	200, // offset
    100  // limit
);

// Set collectors are also available
Set<Person> set = query.toSet(...);

Optional first entity

GigaQuery<Person> query = gigaMap.query(...);
Optional<Person> optFirst = query.findFirst();
optFirst.ifPresent(person -> ...);

Count results

GigaQuery<Person> query = gigaMap.query(...);
long count = query.count();