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import { HttpClient } from '@angular/common/http'
import { Injectable, inject } from '@angular/core'
import {
QueryClient,
mutationOptions,
queryOptions,
} from '@tanstack/angular-query-experimental'
import { lastValueFrom } from 'rxjs'
@Injectable({
providedIn: 'root',
})
export class TasksService {
#queryClient = inject(QueryClient) // Manages query state and caching
#http = inject(HttpClient) // Handles HTTP requests
/**
* Fetches all tasks from the API.
* Returns an observable containing an array of task strings.
*/
allTasks = () =>
queryOptions({
queryKey: ['tasks'],
queryFn: () => {
return lastValueFrom(this.#http.get<Array<string>>('/api/tasks'))
},
})
/**
* Creates a mutation for adding a task.
* On success, invalidates and refetches the "tasks" query cache to update the task list.
*/
addTask() {
return mutationOptions({
mutationFn: ({
task,
failMutation = false,
}: {
task: string
failMutation: boolean
}) =>
lastValueFrom(
this.#http.post(
`/api/tasks${failMutation ? '-wrong-url' : ''}`,
task,
),
),
mutationKey: ['tasks'],
onSuccess: () => {
this.#queryClient.invalidateQueries({ queryKey: ['tasks'] })
},
onMutate: async ({ task }) => {
// Cancel any outgoing refetches
// (so they don't overwrite our optimistic update)
await this.#queryClient.cancelQueries({ queryKey: ['tasks'] })
// Snapshot the previous value
const previousTodos = this.#queryClient.getQueryData<Array<string>>([
'tasks',
])
// Optimistically update to the new value
if (previousTodos) {
this.#queryClient.setQueryData<Array<string>>(
['tasks'],
[...previousTodos, task],
)
}
return previousTodos
},
onError: (err, variables, context) => {
if (context) {
this.#queryClient.setQueryData<Array<string>>(['tasks'], context)
}
},
// Always refetch after error or success:
onSettled: () => {
this.#queryClient.invalidateQueries({ queryKey: ['tasks'] })
},
})
}
}
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