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Mutations

Unlike queries, mutations are typically used to create/update/delete data or perform server side-effects. For this purpose, React Query exports a useMutation hook.

Here's an example of a mutation that adds a new todo to the server:

tsx
function App() {
const mutation = useMutation({
mutationFn: newTodo => {
return axios.post('/todos', newTodo)
}
})
return (
<div>
{mutation.isLoading ? (
'Adding todo...'
) : (
<>
{mutation.isError ? (
<div>An error occurred: {mutation.error.message}</div>
) : null}
{mutation.isSuccess ? <div>Todo added!</div> : null}
<button
onClick={() => {
mutation.mutate({ id: new Date(), title: 'Do Laundry' })
}}
>
Create Todo
</button>
</>
)}
</div>
)
}

A mutation can only be in one of the following states at any given moment:

  • isIdle or status === 'idle' - The mutation is currently idle or in a fresh/reset state
  • isLoading or status === 'loading' - The mutation is currently running
  • isError or status === 'error' - The mutation encountered an error
  • isSuccess or status === 'success' - The mutation was successful and mutation data is available

Beyond those primary states, more information is available depending on the state of the mutation:

  • error - If the mutation is in an error state, the error is available via the error property.
  • data - If the mutation is in a success state, the data is available via the data property.

In the example above, you also saw that you can pass variables to your mutations function by calling the mutate function with a single variable or object.

Even with just variables, mutations aren't all that special, but when used with the onSuccess option, the Query Client's invalidateQueries method and the Query Client's setQueryData method, mutations become a very powerful tool.

IMPORTANT: The mutate function is an asynchronous function, which means you cannot use it directly in an event callback in React 16 and earlier. If you need to access the event in onSubmit you need to wrap mutate in another function. This is due to React event pooling.

tsx
// This will not work in React 16 and earlier
const CreateTodo = () => {
const mutation = useMutation({ mutationFn: event => {
event.preventDefault()
return fetch('/api', new FormData(event.target))
}})
return <form onSubmit={mutation.mutate}>...</form>
}
// This will work
const CreateTodo = () => {
const mutation = useMutation({ mutationFn: formData => {
return fetch('/api', formData)
}})
const onSubmit = event => {
event.preventDefault()
mutation.mutate(new FormData(event.target))
}
return <form onSubmit={onSubmit}>...</form>
}

Resetting Mutation State

It's sometimes the case that you need to clear the error or data of a mutation request. To do this, you can use the reset function to handle this:

tsx
const CreateTodo = () => {
const [title, setTitle] = useState('')
const mutation = useMutation({ mutationFn: createTodo })
const onCreateTodo = e => {
e.preventDefault()
mutation.mutate({ title })
}
return (
<form onSubmit={onCreateTodo}>
{mutation.error && (
<h5 onClick={() => mutation.reset()}>{mutation.error}</h5>
)}
<input
type="text"
value={title}
onChange={e => setTitle(e.target.value)}
/>
<br />
<button type="submit">Create Todo</button>
</form>
)
}

Mutation Side Effects

useMutation comes with some helper options that allow quick and easy side-effects at any stage during the mutation lifecycle. These come in handy for both invalidating and refetching queries after mutations and even optimistic updates

tsx
useMutation({
mutationFn: addTodo,
onMutate: variables => {
// A mutation is about to happen!
// Optionally return a context containing data to use when for example rolling back
return { id: 1 }
},
onError: (error, variables, context) => {
// An error happened!
console.log(`rolling back optimistic update with id ${context.id}`)
},
onSuccess: (data, variables, context) => {
// Boom baby!
},
onSettled: (data, error, variables, context) => {
// Error or success... doesn't matter!
},
})

When returning a promise in any of the callback functions it will first be awaited before the next callback is called:

tsx
useMutation({
mutationFn: addTodo,
onSuccess: async () => {
console.log("I'm first!")
},
onSettled: async () => {
console.log("I'm second!")
},
})

You might find that you want to trigger additional callbacks beyond the ones defined on useMutation when calling mutate. This can be used to trigger component-specific side effects. To do that, you can provide any of the same callback options to the mutate function after your mutation variable. Supported overrides include: onSuccess, onError and onSettled. Please keep in mind that those additional callbacks won't run if your component unmounts before the mutation finishes.

tsx
useMutation({
mutationFn: addTodo,
onSuccess: (data, variables, context) => {
// I will fire first
},
onError: (error, variables, context) => {
// I will fire first
},
onSettled: (data, error, variables, context) => {
// I will fire first
},
})
mutate(todo, {
onSuccess: (data, variables, context) => {
// I will fire second!
},
onError: (error, variables, context) => {
// I will fire second!
},
onSettled: (data, error, variables, context) => {
// I will fire second!
},
})

Consecutive mutations

There is a slight difference in handling onSuccess, onError and onSettled callbacks when it comes to consecutive mutations. When passed to the mutate function, they will be fired up only once and only if the component is still mounted. This is due to the fact that mutation observer is removed and resubscribed every time when the mutate function is called. On the contrary, useMutation handlers execute for each mutate call.

Be aware that most likely, mutationFn passed to useMutation is asynchronous. In that case, the order in which mutations are fulfilled may differ from the order of mutate function calls.

tsx
useMutation({
mutationFn: addTodo,
onSuccess: (data, error, variables, context) => {
// Will be called 3 times
},
})
['Todo 1', 'Todo 2', 'Todo 3'].forEach((todo) => {
mutate(todo, {
onSuccess: (data, error, variables, context) => {
// Will execute only once, for the last mutation (Todo 3),
// regardless which mutation resolves first
},
})
})

Promises

Use mutateAsync instead of mutate to get a promise which will resolve on success or throw on an error. This can for example be used to compose side effects.

tsx
const mutation = useMutation({ mutationFn: addTodo })
try {
const todo = await mutation.mutateAsync(todo)
console.log(todo)
} catch (error) {
console.error(error)
} finally {
console.log('done')
}

Retry

By default React Query will not retry a mutation on error, but it is possible with the retry option:

tsx
const mutation = useMutation({
mutationFn: addTodo,
retry: 3,
})

If mutations fail because the device is offline, they will be retried in the same order when the device reconnects.

Persist mutations

Mutations can be persisted to storage if needed and resumed at a later point. This can be done with the hydration functions:

tsx
const queryClient = new QueryClient()
// Define the "addTodo" mutation
queryClient.setMutationDefaults(['addTodo'], {
mutationFn: addTodo,
onMutate: async (variables) => {
// Cancel current queries for the todos list
await queryClient.cancelQueries({ queryKey: ['todos'] })
// Create optimistic todo
const optimisticTodo = { id: uuid(), title: variables.title }
// Add optimistic todo to todos list
queryClient.setQueryData(['todos'], old => [...old, optimisticTodo])
// Return context with the optimistic todo
return { optimisticTodo }
},
onSuccess: (result, variables, context) => {
// Replace optimistic todo in the todos list with the result
queryClient.setQueryData(['todos'], old => old.map(todo => todo.id === context.optimisticTodo.id ? result : todo))
},
onError: (error, variables, context) => {
// Remove optimistic todo from the todos list
queryClient.setQueryData(['todos'], old => old.filter(todo => todo.id !== context.optimisticTodo.id))
},
retry: 3,
})
// Start mutation in some component:
const mutation = useMutation({ mutationKey: ['addTodo'] })
mutation.mutate({ title: 'title' })
// If the mutation has been paused because the device is for example offline,
// Then the paused mutation can be dehydrated when the application quits:
const state = dehydrate(queryClient)
// The mutation can then be hydrated again when the application is started:
hydrate(queryClient, state)
// Resume the paused mutations:
queryClient.resumePausedMutations()

Persisting Offline mutations

If you persist offline mutations with the persistQueryClient plugin, mutations cannot be resumed when the page is reloaded unless you provide a default mutation function.

This is a technical limitation. When persisting to an external storage, only the state of mutations is persisted, as functions cannot be serialized. After hydration, the component that triggers the mutation might not be mounted, so calling resumePausedMutations might yield an error: No mutationFn found.

tsx
const persister = createSyncStoragePersister({
storage: window.localStorage,
})
const queryClient = new QueryClient({
defaultOptions: {
queries: {
cacheTime: 1000 * 60 * 60 * 24, // 24 hours
},
},
})
// we need a default mutation function so that paused mutations can resume after a page reload
queryClient.setMutationDefaults(['todos'], {
mutationFn: ({ id, data }) => {
return api.updateTodo(id, data)
},
})
export default function App() {
return (
<PersistQueryClientProvider
client={queryClient}
persistOptions={{ persister }}
onSuccess={() => {
// resume mutations after initial restore from localStorage was successful
queryClient.resumePausedMutations()
}}
>
<RestOfTheApp />
</PersistQueryClientProvider>
)
}

We also have an extensive offline example that covers both queries and mutations.

Further reading

For more information about mutations, have a look at #12: Mastering Mutations in React Query from the Community Resources.