Optimistic Updates
When you're performing an update on some data that already exists in the cache via useMutation, RTK Query gives you a few tools to implement an optimistic update. This can be a useful pattern for when you want to give the user the impression that their changes are immediate.
The core concepts are:
- in the
onStartphase of a mutation, you manually set the cached data viaupdateQueryResult - then, in
onError, you roll it back viapatchQueryResult. You don't have to worry about theonSuccesslifecycle here.
Example optimistic update mutation
const api = createApi({
baseQuery,
entityTypes: ['Post'],
endpoints: (build) => ({
getPost: build.query<Post, string>({ query: (id) => `post/${id}`, provides: ['Post'] }),
updatePost: build.mutation<void, Pick<Post, 'id'> & Partial<Post>, { undoPost: Patch[] }>({
query: ({ id, ...patch }) => ({ url: `post/${id}`, method: 'PATCH', body: patch }),
onStart({ id, ...patch }, { dispatch, context }) {
// When we start the request, just immediately update the cache
context.undoPost = dispatch(
api.util.updateQueryResult('getPost', id, (draft) => {
Object.assign(draft, patch);
})
).inversePatches;
},
onError({ id }, { dispatch, context }) {
// If there is an error, roll it back
dispatch(api.util.patchQueryResult('getPost', id, context.undoPost));
},
invalidates: ['Post'],
}),
}),
});