Live Query

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    Description — Working with Couchbase Lite’s data model  — Querying database data using 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(); (1)
    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.
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