Pagination & Refetching

Fetching new data for an OperationRequest in Ferry is as easy as adding an updated request to the Client.requestController. Ferry will automatically include the results from the updated request in the response Stream of the original request if:

  1. The updated request is identical to the original request, OR
  2. The updated request has the same (non-null) requestId as the original request

Refetching

For example, if we are listening to the following request:

final reviewsReq = GReviewsReq(
(b) => b
..vars.first = 3
..vars.offset = 0,
);
client.request(reviewsReq).listen((response) => print(response));

We can refetch the query by adding the same request to the requestController:

client.requestController.add(reviewsReq);

Once the response is received, any request() Streams that were listening to reviewsReq will get updated with the new data.

note

Since refetching doesn't override the FetchPolicy setting, if FetchPolicy is set to CacheFirst, you'll get the cached results of the initial operation.

Pagination

Rather than just replacing the previous result with the refetched result, we may want to combine the results to enable pagination.

To do this, we first need to update our original request to include a requestId. This will tell Ferry to include any results from subsequent requests with the same requestId in this request's result stream.

final reviewsReq = GReviewsReq(
(b) => b
..requestId = 'MyReviewsReq'
..vars.first = 3
..vars.offset = 0,
);
client.request(reviewsReq).listen((response) => print(response));

Now we can create a copy of our request that will fetch the next set of results and include an updateResult calback that tells ferry how to combine the results.

For example, let's fetch the next 3 reviews.

final nextReviewsReq = reviewsReq.rebuild(
(b) => b
..vars.offset = 3
..updateResult = (previous, result) =>
previous?.rebuild((b) => b..reviews.addAll(result.reviews)) ??
result,
);
client.requestController.add(nextReviewsReq);
note

Since we are using the rebuild() method, our newsReviewsReq will copy the requestId we defined in reviewsReq above automatically. Otherwise, we'd need to specify the requestId manuallly.

The next event received by our request() Stream will now include all six reviews.

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