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alxhubAndrewKushnir
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AndrewKushnir
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refactor(core): port resource() to linkedSignal() (#59024)
When the reactive `request` of a resource() notifies, it transitions to the Loading state, fires the loader, and eventually transitions to Resolved. With the prior implementation, a change of the `request` will queue the effect, but the state remains unchanged until the effect actually runs. For a brief period, the resource is in a state where the request has changed, but the state has yet to update. This is problematic if we want to use resources in certain contexts where we care about the state of the resource in a synchronous way. For example, an async validator backed by a resource might be checked after an update: ``` value.set(123); if (validator.value()) { // value is still valid, even though the resource is dirty and will soon // flip to loading state (returning value(): undefined) while revalidating } ``` To address this timing concern, `linkedSignal()` is used within the `resource()` to synchronously transition the state in response to the request changing. This ensures any followup reads see a consistent view of the resource regardless of whether the effect has run. This also addresses a race condition where `.set()` behaves differently on a `resource()` depending on whether or not the effect has run. PR Close #59024
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‎packages/core/rxjs-interop/test/rx_resource_spec.ts‎

Lines changed: 9 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -26,12 +26,14 @@ describe('rxResource()', () => {
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it('should cancel the fetch when a new request comes in', async () => {
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const injector = TestBed.inject(Injector);
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const appRef = TestBed.inject(ApplicationRef);
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let unsub = false;
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const request = signal(1);
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const res = rxResource({
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let unsub = false;
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let lastSeenRequest: number = 0;
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rxResource({
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request,
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loader: ({request}) =>
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new Observable((sub) => {
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loader: ({request}) => {
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lastSeenRequest = request;
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return new Observable((sub) => {
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if (request === 2) {
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sub.next(true);
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}
@@ -40,12 +42,13 @@ describe('rxResource()', () => {
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unsub = true;
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}
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};
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}),
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});
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},
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injector,
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});
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// Wait for the resource to reach loading state.
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await waitFor(() => res.isLoading());
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await waitFor(() => lastSeenRequest === 1);
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// Setting request = 2 should cancel request = 1
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request.set(2);

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