Live Query — Working with Queries
Description — Couchbase Lite database data querying concepts — live queries
Related Content — Predictive Query | Indexing | Queries
Activating a Live Query
A live query is a query that, once activated, remains active and monitors the database for changes; refreshing the result set whenever a change occurs. As such, it is a great way to build reactive user interfaces — especially table/list views — that keep themselves up to date.
So, a simple use case may be: A replicator running and pulling new data from a server, whilst a live-query-driven UI automatically updates to show the data without the user having to manually refresh. This helps your app feel quick and responsive.
Example 1. Starting a LIve Query
Query query = QueryBuilder
.select(SelectResult.all())
.from(DataSource.database(database));
// Adds a query change listener.
// Changes will be posted on the main queue.
ListenerToken token = query.addChangeListener(change -> { (1)
for (Result result : change.getResults()) {
Log.d(TAG, "results: " + result.getKeys());
/* Update UI */
}
});
// Start live query.
query.execute(); (2)| 1 | Build the query statements using the QuerybUilder |
| 2 | Activate the live query by attaching a listener. Save the token in order to detach the listener and stop the query later — se Example 2 |
| 3 | Start the query This will immediately execute the live query and post the result to the change listener. When a change is detected the query automatically runs, and posts the new query result to any observers (change listeners). |
Example 2. Stop a LIve Query
query.removeChangeListener(token); (1)| 1 | Here we use the change lister token from Example 1 to remove the listeners. Doing so stops the live query. |