Live Queries
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).
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 |
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. |