Live Queries

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    Couchbase mobile database live query concepts

    Overview

    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
    var query = QueryBuilder
        .Select(SelectResult.All())
        .From(DataSource.Database(db));
    
    // Adds a query change listener.
    // Changes will be posted on the main queue.
    var token = query.AddChangeListener((sender, args) => (1)
    {
        var allResult = args.Results.AllResults();
        foreach (var result in allResult) {
            Console.WriteLine(result.Keys);
            /* 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);
    query.Dispose();
    1 Here we use the change lister token from Example 1 to remove the listeners. Doing so stops the live query.