Subscriptions
Executing a GraphQL Subscription with Ferry is similar to queries, but with a few key differences:
- Setting up a WebSocket link for subscriptions
- Listening to the returned Stream for real-time updates
Setting up WebSocket Link
First, you need to set up a WebSocket link for subscriptions. You can use the gql_websocket_link package for this. To add it to your project, run:
(if using apollo use the TransportWebSocketLink)
dependencies:
gql_websocket_link:
create the link:
Link.split(
(request) =>
request.operation.getOperationType() == OperationType.subscription,
TransportWebSocketLink(
TransportWsClientOptions(
socketMaker: WebSocketMaker.url(() => 'ws://<your url>/graphql'),
connectionParams: () =>
// add your auth headers here
webSocketHeaders),
),
DioLink('https://<your url>/graphql', client: dio, defaultHeaders: headers),
)
Creating the GraphQL Subscription Request
Let's say we have a NewReviews Subscription saved in a file named new_reviews.graphql:
subscription NewReviews {
newReviews {
id
title
content
author {
id
name
}
}
}
after the file is created run your codegen command.
Using the Subscription
Now that we have our subscription set up, we can use it in our Dart code. Here's an example of how to use the NewReviews subscription:
Stream<NewReviews?> getNewReviews() {
final request = GNewReviewsReq();
try {
final resultStream = _ferryService.request<GNewReviewsData, GNewReviewsVars>(request);
return resultStream.asyncMap((response) {
final data = response.data?.newReviews;
if (data != null) {
return NewReviews(
id: data.id,
title: data.title,
content: data.content,
author: data.author,
);
}
return null;
});
} catch (e) {
print('Failed to get new reviews: $e');
rethrow;
}
}