# Invalidations from Mutations

Invalidating queries is only half the battle. Knowing **when** to invalidate them is the other half. Usually when a mutation in your app succeeds, it's VERY likely that there are related queries in your application that need to be invalidated and possibly refetched to account for the new changes from your mutation.

For example, assume we have a mutation to post a new todo:



```tsx
const mutation = useMutation({ mutationFn: postTodo })
```



When a successful `postTodo` mutation happens, we likely want all `todos` queries to get invalidated and possibly refetched to show the new todo item. To do this, you can use `useMutation`'s `onSuccess` options and the `client`'s `invalidateQueries` function:



```tsx
import { useMutation, useQueryClient } from '@tanstack/react-query'

const queryClient = useQueryClient()

// When this mutation succeeds, invalidate any queries with the `todos` or `reminders` query key
const mutation = useMutation({
  mutationFn: addTodo,
  onSuccess: async () => {
    // If you're invalidating a single query
    await queryClient.invalidateQueries({ queryKey: ['todos'] })

    // If you're invalidating multiple queries
    await Promise.all([
      queryClient.invalidateQueries({ queryKey: ['todos'] }),
      queryClient.invalidateQueries({ queryKey: ['reminders'] }),
    ])
  },
})
```



Returning a Promise on `onSuccess` makes sure the data is updated before the mutation is entirely complete (i.e., isPending is true until onSuccess is fulfilled)



```tsx
import { useMutation, useQueryClient } from '@tanstack/vue-query'

const queryClient = useQueryClient()

// When this mutation succeeds, invalidate any queries with the `todos` or `reminders` query key
const mutation = useMutation({
  mutationFn: addTodo,
  onSuccess: () => {
    queryClient.invalidateQueries({ queryKey: ['todos'] })
    queryClient.invalidateQueries({ queryKey: ['reminders'] })
  },
})
```



## Further reading

For a technique to automatically invalidate Queries after Mutations, have a look at [TkDodo's article on Automatic Query Invalidation after Mutations](https://tkdodo.eu/blog/automatic-query-invalidation-after-mutations).