Live Queries

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      Couchbase mobile database live query concepts

      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 = QueryBuilder
          .select(SelectResult.all())
          .from(DataSource.database(database)) (1)
      
      // Adds a query change listener.
      // Changes will be posted on the main queue.
      let token = query.addChangeListener { (change) in (2)
          for result in change.results! {
              print(result.keys)
              /* Update UI */
          }
      } (3)
      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(withToken: token) (1)
      1 Here we use the change lister token from Example 1 to remove the listener. Doing so stops the live query.