Live Queries

      +

      Description — 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
      CBLQuery query = [CBLQueryBuilder select:@[[CBLQuerySelectResult all]]
                                           from:[CBLQueryDataSource database:self.database]]; (1)
      
      // Adds a query change listener.
      // Changes will be posted on the main queue.
      id<CBLListenerToken> token = [query addChangeListener:^(CBLQueryChange  *change) { (2)
          for (CBLQueryResultSet *results in [change results]) {
              NSLog(@"%@", results);
              / 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 removeChangeListenerWithToken:token]; (1)
      1 Here we use the change lister token from Example 1 to remove the listener. Doing so stops the live query.