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(graphcache) - Fix offlineExchange timing after rehydration #1019

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Sep 30, 2020
Merged

(graphcache) - Fix offlineExchange timing after rehydration #1019

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c8424e2
Add experimental buffer fix for edge cases in Svelte/Preact
kitten Sep 30, 2020
4fcc210
Add changeset
kitten Sep 30, 2020
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5 changes: 5 additions & 0 deletions .changeset/ninety-plants-peel.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@urql/exchange-graphcache': patch
---

Fix a case where the `offlineExchange` would not start processing operations after hydrating persisted data when no operations arrived in time by the time the persisted data was restored. This would be more evident in Preact and Svelte due to their internal short timings.
14 changes: 10 additions & 4 deletions exchanges/graphcache/src/cacheExchange.ts
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Expand Up @@ -11,13 +11,14 @@ import {

import {
filter,
combine,
scan,
map,
merge,
pipe,
share,
fromPromise,
fromArray,
buffer,
take,
mergeMap,
concat,
Expand Down Expand Up @@ -249,10 +250,15 @@ export const cacheExchange = (opts?: CacheExchangeOpts): Exchange => ({
// If no hydration takes place we replace this stream with an empty one
const bufferedOps$ = hydration
? pipe(
sharedOps$,
buffer(fromPromise(hydration)),
combine(
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This works because combine can retroactively still resolve an operation synchronously once the first operation comes in. This lets bufferedOps$ hang in its active state for as long or short as needed.

buffer on the other hand may not emit when its list of values is empty, but would wait for the next signal if then a new event comes in. Because we'd before only wait for one buffer output though and have one input event, there are conditions where bufferedOps$ would stay active indefinitely.

pipe(
sharedOps$,
scan((acc: Operation[], x) => (acc.push(x), acc), [])
),
fromPromise(hydration)
),
take(1),
mergeMap(fromArray)
mergeMap(zip => fromArray(zip[0]))
)
: (empty as Source<Operation>);

Expand Down