Optimistic mutation: temporary duplicate responses

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1

Hi. I’m trying to add optimistic response to a mutation sendMessage. In terms of business logic, this mutation adds a new message to a chat channel. I’m encountering a bug where if I send messages “1” “2” “3” in rapid succession on an artificially throttled network, I’ll see:

duplicate.mov - Google Drive (screen recording)

I’ve consulted these docs:

  • https://www.apollographql.com/docs/react/performance/optimistic-ui
  • https://www.apollographql.com/docs/react/caching/cache-interaction
  • https://www.apollographql.com/docs/react/data/mutations#updating-the-cache-directly

My code is something like:

const content = /* get content from input field */
/* clear input field so user can immediately start typing another message */
const temporaryId = `temp-id-${Date.now()}`;
const optimisticResponse = {
  sendMessage: {
    __typename: "Message" as const,
    id: temporaryId,
    content,
    ...
  }
}
await sendMessage({
  variables: {...},
  optimisticResponse,
  update: (cache, { data: { sendMessage: newMessage } }) => {
    ... /* I've tried various approaches here */
  }
});

The UI renders messages that are nested in the results of another query, channelById, which returns a Channel type.

My understanding is:

  • Since I’ve specified optimisticResponse, the Apollo client will immediately add the optimistic message to the cache once the mutation is triggered.
  • The messages list deep inside the channelById result may not necessarily be automatically updated, so I would have to manually define how to update that part of the cache by writing an update function. In practice, it seems that messages does update automatically, and the update function isn’t needed?

I’ve tried passing several different update functions into the mutation (including no function) and they all lead to this behavior.

Does anyone know how to fix this?

2

Bump, still would appreciate help with this! Happy to provide more details/context if useful.