Does a custom action also invoke collection-level handlers if you use the collection's default operations in its useMutate method?

[aihdene-genetec]

I am reading through the documentation and came through the optimistic custom actions:

// Intent: "like this post"
const likePost = createOptimisticAction<string>({
  onMutate: (postId) => {
    // Optimistic guess at the change
    postCollection.update(postId, (draft) => {
      draft.likeCount += 1
      draft.likedByMe = true
    })
  },
  mutationFn: async (postId) => {
    // Send the intent to the server
    await api.posts.like(postId)
    // Server determines actual state changes
    await postCollection.utils.refetch()
  },
})

// Use it.
likePost(postId)

Documentation states that you can use custom actions when:

You want to send user intent to the backend rather than exact state changes

The action calls api.posts.like(postId) but it also calls postCollection.update which from my understanding might invoke onUpdate collection-level handler. Which means that you'd have two potential calls to the back-end? Or am I incorrect in my assumption?

Thank you for your time and consideration.

[barry166]

Yes, that assumption is correct: postCollection.update(...) is still a normal collection mutation, so if the collection has an onUpdate persistence handler, that handler can run too.

For this pattern, do not have both paths write the same backend change. Either:

onMutate: (postId) => {
  postCollection.update(postId, draft => {
    draft.likeCount += 1
    draft.likedByMe = true
  })
},
mutationFn: async (postId) => {
  await api.posts.like(postId)
  await postCollection.utils.refetch()
}

and make sure the collection-level onUpdate is not also persisting that optimistic update, or skip the custom action and let the collection onUpdate be the single persistence path. Custom actions are best when the backend API is intent-shaped (likePost) rather than patch-shaped (update post fields).