Mirror: The highly customizable and versatile GraphQL client with which you add on features like normalized caching as you grow.
docs(core): Update subscription instructions (#3127)
authored by
Phil Pluckthun
and committed by
GitHub
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docs/advanced/subscriptions.md
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docs/advanced/subscriptions.md
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In the above example, we add the `subscriptionExchange` to the `Client` with the default exchanges
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added before it. The `subscriptionExchange` is a factory that accepts additional options and returns
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the actual `Exchange` function. It does not make any assumption over the transport protocol and
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scheme that is used. Instead, we need to pass a `forwardSubscription` function, which is called with
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an "enriched" _Operation_ every time the `Client` attempts to execute a GraphQL Subscription.
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scheme that is used. Instead, we need to pass a `forwardSubscription` function.
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The `forwardSubscription` is called when the `subscriptionExchange` receives an `Operation`, so
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typically, when you’re executing a GraphQL subscription. This will call the `forwardSubscription`
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function with a GraphQL request body, in the same shape that a GraphQL HTTP API may receive it as
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JSON input.
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If you’re using TypeScript, you may notice that the input that `forwardSubscription` receives has
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an optional `query` property. This is because of persisted query support. For some transports, the
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`query` property may have to be defaulted to an empty string, which matches the GraphQL over HTTP
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specification more closely.
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When we define this function it must return an "Observable-like" object, which needs to follow the
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[Observable spec](https://github.com/tc39/proposal-observable), which comes down to having an
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cacheExchange,
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fetchExchange,
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subscriptionExchange({
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forwardSubscription: request => ({
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subscribe: sink => ({
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unsubscribe: wsClient.subscribe(request, sink),
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}),
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}),
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forwardSubscription(request) {
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const input = { ...request, query: request.query || '' };
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return {
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subscribe(sink) {
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const unsubscribe = wsClient.subscribe(input, sink);
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return { unsubscribe };
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},
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};
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},
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}),
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],
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});