Live Query

    +

    Description — Working with Couchbase Lite’s data model  — Querying database data using live queries
    Related Content — Predictive Queries | Indexing | QueryBuilder

    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.

    To activate a LiveQuery just add a change listener to the query statement. It will be immediately active. When a change is detected the query automatically runs, and posts the new query result to any observers (change listeners).

    Example 1. Starting a Live Query
    Query query = QueryBuilder
        .select(SelectResult.all())
        .from(DataSource.database(database)); (1)
    
    // Adds a query change listener.
    // Changes will be posted on the main queue.
    ListenerToken token = query.addChangeListener(change -> { (2)
        for (Result result : change.getResults()) {
            Log.d(TAG, "results: " + result.getKeys());
            /* Update UI */
        }
    });
    1 Build the query statements
    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
    Example 2. Stop a LIve Query
    query.removeChangeListener(token); (1)
    1 Here we use the change lister token from Example 1 to remove the listener. Doing so stops the live query.