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Manual Cache Updates

Overview​

For most cases, in order to receive up to date data after a triggering a change in the backend, you can take advantage of cache tag invalidation to perform automated re-fetching. This will cause a query to re-fetch its data when it has been told that a mutation has occurred which would cause its data to become out of date.

We recommend using automated re-fetching as a preference over manual cache updates in most situations.

However, there are use cases when manual cache updates are necessary, such as "optimistic" or "pessimistic" updates, or modifying data as part of cache entry lifecycles.

RTK Query exports thunks for these use cases, attached to api.utils:

Since these are thunks, you can dispatch them anywhere you have access to dispatch.

Updating existing cache entries​

For updates of existing cache entries, use updateQueryData.

updateQueryData is strictly intended to perform updates to existing cache entries, not create new entries. If an updateQueryData thunk action is dispatched and the endpointName + args combination that does not match any existing cache entry, the provided recipe callback will not be called, and no patches or inversePatches will be returned.

Use cases for manual update of cache entries:

  • Providing immediate feedback to the user when a mutation is attempted
  • After a mutation, updating a single item in a large list of items that is already cached, rather than re-fetching the whole list
  • Debouncing a large number of mutations with immediate feedback as though they are being applied, followed by a single request sent to the server to update the debounced attempts

Creating new cache entries or replacing existing ones​

To create or replace existing cache entries, use upsertQueryData.

upsertQueryData is intended to perform replacements to existing cache entries or creation of new ones. Since upsertQueryData does not have access to the previous state of the cache entry, the update may be performed only as a replacement. In comparison, updateQueryData allows patching of the existing cache entry, but cannot create a new one.

One example use case is pessimistic updates. If the client makes an API call to create a Post, the backend could return its complete data including the id. Then we can use upsertQueryData to create a new cache entry for the getPostById(id) query, preventing an extra fetch to retrieve the item later.

Recipes​

Optimistic Updates​

When you wish to perform an update to cache data immediately after a mutation is triggered, you can apply an optimistic update. This can be a useful pattern for when you want to give the user the impression that their changes are immediate, even while the mutation request is still in flight.

The core concepts for an optimistic update are:

  • when you start a query or mutation, onQueryStarted will be executed
  • you manually update the cached data by dispatching api.util.updateQueryData within onQueryStarted
  • then, in the case that queryFulfilled rejects:
    • you roll it back via the .undo property of the object you got back from the earlier dispatch, OR
    • you invalidate the cache data via api.util.invalidateTags to trigger a full re-fetch of the data
tip

Where many mutations are potentially triggered in short succession causing overlapping requests, you may encounter race conditions if attempting to roll back patches using the .undo property on failures. For these scenarios, it is often simplest and safest to invalidate the tags on error instead, and re-fetch truly up-to-date data from the server.

Optimistic update mutation example (async await)
import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query'
import type { Post } from './types'

const api = createApi({
  baseQuery: fetchBaseQuery({
    baseUrl: '/',
  }),
  tagTypes: ['Post'],
  endpoints: (build) => ({
    getPost: build.query<Post, number>({
      query: (id) => `post/${id}`,
      providesTags: ['Post'],
    }),
    updatePost: build.mutation<void, Pick<Post, 'id'> & Partial<Post>>({
      query: ({ id, ...patch }) => ({
        url: `post/${id}`,
        method: 'PATCH',
        body: patch,
      }),
      async onQueryStarted({ id, ...patch }, { dispatch, queryFulfilled }) {
        const patchResult = dispatch(
          api.util.updateQueryData('getPost', id, (draft) => {
            Object.assign(draft, patch)
          })
        )
        try {
          await queryFulfilled
        } catch {
          patchResult.undo()

          /**
           * Alternatively, on failure you can invalidate the corresponding cache tags
           * to trigger a re-fetch:
           * dispatch(api.util.invalidateTags(['Post']))
           */
        }
      },
    }),
  }),
})

or, if you prefer the slightly shorter version with .catch

-      async onQueryStarted({ id, ...patch }, { dispatch, queryFulfilled }) {
+      onQueryStarted({ id, ...patch }, { dispatch, queryFulfilled }) {
        const patchResult = dispatch(
          api.util.updateQueryData('getPost', id, (draft) => {
            Object.assign(draft, patch)
          })
        )
-       try {
-         await queryFulfilled
-       } catch {
-         patchResult.undo()
-       }
+       queryFulfilled.catch(patchResult.undo)
      }

Example​

React Optimistic Updates

Pessimistic Updates​

When you wish to perform an update to cache data based on the response received from the server after a mutation is triggered, you can apply a pessimistic update. The distinction between a pessimistic update and an optimistic update is that the pessimistic update will instead wait for the response from the server prior to updating the cached data.

The core concepts for a pessimistic update are:

  • when you start a query or mutation, onQueryStarted will be executed
  • you await queryFulfilled to resolve to an object containing the transformed response from the server in the data property
  • you manually update the cached data by dispatching api.util.updateQueryData within onQueryStarted, using the data in the response from the server for your draft updates
  • you manually create a new cache entry by dispatching api.util.upsertQueryData within onQueryStarted, using the complete Post object returned by backend.
Pessimistic update mutation example (async await)
import { createApi, fetchBaseQuery } from '@reduxjs/toolkit/query'
import type { Post } from './types'

const api = createApi({
  baseQuery: fetchBaseQuery({
    baseUrl: '/',
  }),
  tagTypes: ['Post'],
  endpoints: (build) => ({
    getPost: build.query<Post, number>({
      query: (id) => `post/${id}`,
      providesTags: ['Post'],
    }),
    updatePost: build.mutation<Post, Pick<Post, 'id'> & Partial<Post>>({
      query: ({ id, ...patch }) => ({
        url: `post/${id}`,
        method: 'PATCH',
        body: patch,
      }),
      async onQueryStarted({ id, ...patch }, { dispatch, queryFulfilled }) {
        try {
          const { data: updatedPost } = await queryFulfilled
          const patchResult = dispatch(
            api.util.updateQueryData('getPost', id, (draft) => {
              Object.assign(draft, updatedPost)
            })
          )
        } catch {}
      },
    }),
    createPost: build.mutation<Post, Pick<Post, 'id'> & Partial<Post>>({
      query: ({ id, ...body }) => ({
        url: `post/${id}`,
        method: 'POST',
        body,
      }),
      async onQueryStarted({ id }, { dispatch, queryFulfilled }) {
        try {
          const { data: createdPost } = await queryFulfilled
          const patchResult = dispatch(
            api.util.upsertQueryData('getPost', id, createdPost)
          )
        } catch {}
      },
    }),
  }),
})

General Updates​

If you find yourself wanting to update cache data elsewhere in your application, you can do so anywhere you have access to the store.dispatch method, including within React components via the useDispatch hook (or a typed version such as useAppDispatch for typescript users).

info

You should generally avoid manually updating the cache outside of the onQueryStarted callback for a mutation without a good reason, as RTK Query is intended to be used by considering your cached data as a reflection of the server-side state.

General manual cache update example
import { api } from './api'
import { useAppDispatch } from './store/hooks'

function App() {
  const dispatch = useAppDispatch()

  function handleClick() {
    /**
     * This will update the cache data for the query corresponding to the `getPosts` endpoint,
     * when that endpoint is used with no argument (undefined).
     */
    const patchCollection = dispatch(
      api.util.updateQueryData('getPosts', undefined, (draftPosts) => {
        draftPosts.push({ id: 1, name: 'Teddy' })
      })
    )
  }

  return <button onClick={handleClick}>Add post to cache</button>
}
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