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---
id: optimistic-updates
title: Optimistic Updates
ref: docs/framework/react/guides/optimistic-updates.md
replace:
{
'React': 'Angular',
'useMutation': 'injectMutation',
'hook': 'function',
'useMutationState': 'injectMutationState',
'addTodoMutation': 'addTodo',
}
---
[//]: # 'ExampleUI1'
```ts
addTodo = injectMutation(() => ({
mutationFn: (newTodo: string) => axios.post('/api/data', { text: newTodo }),
// make sure to _return_ the Promise from the query invalidation
// so that the mutation stays in `pending` state until the refetch is finished
onSettled: async () => {
return await queryClient.invalidateQueries({ queryKey: ['todos'] })
},
}))
```
[//]: # 'ExampleUI1'
[//]: # 'ExampleUI2'
```angular-ts
@Component({
template: `
@for (todo of todos.data(); track todo.id) {
<li>{{ todo.title }}</li>
}
@if (addTodo.isPending()) {
<li style="opacity: 0.5">{{ addTodo.variables() }}</li>
}
`,
})
class TodosComponent {}
```
[//]: # 'ExampleUI2'
[//]: # 'ExampleUI3'
```angular-ts
@Component({
template: `
@if (addTodo.isError()) {
<li style="color: red">
{{ addTodo.variables() }}
<button (click)="addTodo.mutate(addTodo.variables())">Retry</button>
</li>
}
`,
})
class TodosComponent {}
```
[//]: # 'ExampleUI3'
[//]: # 'ExampleUI4'
```ts
// somewhere in your app
addTodo = injectMutation(() => ({
mutationFn: (newTodo: string) => axios.post('/api/data', { text: newTodo }),
onSettled: () => queryClient.invalidateQueries({ queryKey: ['todos'] }),
mutationKey: ['addTodo'],
}))
// access variables somewhere else
mutationState = injectMutationState<string>(() => ({
filters: { mutationKey: ['addTodo'], status: 'pending' },
select: (mutation) => mutation.state.variables,
}))
```
[//]: # 'ExampleUI4'
[//]: # 'Example'
```ts
queryClient = inject(QueryClient)
updateTodo = injectMutation(() => ({
mutationFn: updateTodo,
// When mutate is called:
onMutate: async (newTodo) => {
// Cancel any outgoing refetches
// (so they don't overwrite our optimistic update)
await this.queryClient.cancelQueries({ queryKey: ['todos'] })
// Snapshot the previous value
const previousTodos = client.getQueryData(['todos'])
// Optimistically update to the new value
this.queryClient.setQueryData(['todos'], (old) => [...old, newTodo])
// Return a context object with the snapshotted value
return { previousTodos }
},
// If the mutation fails,
// use the context returned from onMutate to roll back
onError: (err, newTodo, context) => {
client.setQueryData(['todos'], context.previousTodos)
},
// Always refetch after error or success:
onSettled: () => {
this.queryClient.invalidateQueries({ queryKey: ['todos'] })
},
}))
```
[//]: # 'Example'
[//]: # 'Example2'
```ts
queryClient = inject(QueryClient)
updateTodo = injectMutation(() => ({
mutationFn: updateTodo,
// When mutate is called:
onMutate: async (newTodo) => {
// Cancel any outgoing refetches
// (so they don't overwrite our optimistic update)
await this.queryClient.cancelQueries({ queryKey: ['todos', newTodo.id] })
// Snapshot the previous value
const previousTodo = this.queryClient.getQueryData(['todos', newTodo.id])
// Optimistically update to the new value
this.queryClient.setQueryData(['todos', newTodo.id], newTodo)
// Return a context with the previous and new todo
return { previousTodo, newTodo }
},
// If the mutation fails, use the context we returned above
onError: (err, newTodo, context) => {
this.queryClient.setQueryData(
['todos', context.newTodo.id],
context.previousTodo,
)
},
// Always refetch after error or success:
onSettled: (newTodo) => {
this.queryClient.invalidateQueries({ queryKey: ['todos', newTodo.id] })
},
}))
```
[//]: # 'Example2'
[//]: # 'Example3'
```ts
injectMutation({
mutationFn: updateTodo,
// ...
onSettled: (newTodo, error, variables, context) => {
if (error) {
// do something
}
},
})
```
[//]: # 'Example3'
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