onSnapshot method
Executes the query and returns the results as Node Stream.
@return A stream of QueryDocumentSnapshot.
Plans and optionally executes this query, and streams the results as Node Stream
of {document?: DocumentSnapshot, metrics?: ExplainMetrics} objects.
The stream surfaces documents one at a time as they are received from the server, and at the end, it will surface the metrics associated with executing the query (if any).
@example
let query = firestore.collection('col').where('foo', '==', 'bar');
let count = 0;
query.explainStream({analyze: true}).on('data', (data) => {
if (data.document) {
// Use data.document which is a DocumentSnapshot instance.
console.log(`Found document with name '${data.document.id}'`);
++count;
}
if (data.metrics) {
// Use data.metrics which is an ExplainMetrics instance.
}
}).on('end', () => {
console.log(`Received ${count} documents.`);
});
@return A stream of {document?: DocumentSnapshot, metrics?: ExplainMetrics}
objects.
Attaches a listener for QuerySnapshot events.
@param onNext A callback to be called every time a new QuerySnapshot
is available.
@param onError A callback to be called if the listen fails or is
cancelled. No further callbacks will occur.
@return An unsubscribe function that can be called to cancel
the snapshot listener.
Implementation
// TODO: Is this possible in dart?
// stream(): NodeJS.ReadableStream;
/// Plans and optionally executes this query, and streams the results as Node Stream
/// of `{document?: DocumentSnapshot, metrics?: ExplainMetrics}` objects.
///
/// The stream surfaces documents one at a time as they are received from the
/// server, and at the end, it will surface the metrics associated with
/// executing the query (if any).
///
/// @example
/// ```
/// let query = firestore.collection('col').where('foo', '==', 'bar');
/// let count = 0;
///
/// query.explainStream({analyze: true}).on('data', (data) => {
/// if (data.document) {
/// // Use data.document which is a DocumentSnapshot instance.
/// console.log(`Found document with name '${data.document.id}'`);
/// ++count;
/// }
/// if (data.metrics) {
/// // Use data.metrics which is an ExplainMetrics instance.
/// }
/// }).on('end', () => {
/// console.log(`Received ${count} documents.`);
/// });
/// ```
///
/// @return A stream of `{document?: DocumentSnapshot, metrics?: ExplainMetrics}`
/// objects.
// TODO: Is this possible in dart?
// explainStream(options?: ExplainOptions): NodeJS.ReadableStream;
/// Attaches a listener for `QuerySnapshot `events.
///
/// @param onNext A callback to be called every time a new `QuerySnapshot`
/// is available.
/// @param onError A callback to be called if the listen fails or is
/// cancelled. No further callbacks will occur.
/// @return An unsubscribe function that can be called to cancel
/// the snapshot listener.
external void onSnapshot(
JSFunction onNext, [
JSFunction onError,
]);