📄 tanstack/query/v4/docs/framework/vue/guides/query-functions

A query function can be literally any function that returns a promise. The promise that is returned should either resolve the data or throw an error.

All of the following are valid query function configurations:

tsx

useQuery({ queryKey: ['todos'], queryFn: fetchAllTodos })
useQuery({ queryKey: ['todos', todoId], queryFn: () => fetchTodoById(todoId) })
useQuery({
  queryKey: ['todos', todoId],
  queryFn: async () => {
    const data = await fetchTodoById(todoId)
    return data
  },
})
useQuery({
  queryKey: ['todos', todoId],
  queryFn: ({ queryKey }) => fetchTodoById(queryKey[1]),
})


useQuery({ queryKey: ['todos'], queryFn: fetchAllTodos })
useQuery({ queryKey: ['todos', todoId], queryFn: () => fetchTodoById(todoId) })
useQuery({
  queryKey: ['todos', todoId],
  queryFn: async () => {
    const data = await fetchTodoById(todoId)
    return data
  },
})
useQuery({
  queryKey: ['todos', todoId],
  queryFn: ({ queryKey }) => fetchTodoById(queryKey[1]),
})

Handling and Throwing Errors
----------------------------

For TanStack Query to determine a query has errored, the query function must throw or return a rejected Promise. Any error that is thrown in the query function will be persisted on the error state of the query.

tsx

const { error } = useQuery({
  queryKey: ['todos', todoId],
  queryFn: async () => {
    if (somethingGoesWrong) {
      throw new Error('Oh no!')
    }
    if (somethingElseGoesWrong) {
      return Promise.reject(new Error('Oh no!'))
    }

    return data
  },
})


const { error } = useQuery({
  queryKey: ['todos', todoId],
  queryFn: async () => {
    if (somethingGoesWrong) {
      throw new Error('Oh no!')
    }
    if (somethingElseGoesWrong) {
      return Promise.reject(new Error('Oh no!'))
    }

    return data
  },
})

Usage with fetch and other clients that do not throw by default
---------------------------------------------------------------

While most utilities like axios or graphql-request automatically throw errors for unsuccessful HTTP calls, some utilities like fetch do not throw errors by default. If that's the case, you'll need to throw them on your own. Here is a simple way to do that with the popular fetch API:

tsx

useQuery({
  queryKey: ['todos', todoId],
  queryFn: async () => {
    const response = await fetch('/todos/' + todoId)
    if (!response.ok) {
      throw new Error('Network response was not ok')
    }
    return response.json()
  },
})


useQuery({
  queryKey: ['todos', todoId],
  queryFn: async () => {
    const response = await fetch('/todos/' + todoId)
    if (!response.ok) {
      throw new Error('Network response was not ok')
    }
    return response.json()
  },
})

Query Function Variables
------------------------

Query keys are not just for uniquely identifying the data you are fetching, but are also conveniently passed into your query function as part of the QueryFunctionContext. While not always necessary, this makes it possible to extract your query functions if needed:

const result = useQuery({
  queryKey: ['todos', { status, page }],
  queryFn: fetchTodoList,
})

// Access the key, status and page variables in your query function!
function fetchTodoList({ queryKey }) {
  const [_key, { status, page }] = queryKey
  return new Promise()
}


const result = useQuery({
  queryKey: ['todos', { status, page }],
  queryFn: fetchTodoList,
})

// Access the key, status and page variables in your query function!
function fetchTodoList({ queryKey }) {
  const [_key, { status, page }] = queryKey
  return new Promise()
}

### QueryFunctionContext

The QueryFunctionContext is the object passed to each query function. It consists of:

queryKey: QueryKey: Query Keys
pageParam?: unknown
- only for Infinite Queries
- the page parameter used to fetch the current page
signal?: AbortSignal
- AbortSignal instance provided by TanStack Query
- Can be used for Query Cancellation
meta: Record<string, unknown> | undefined
- an optional field you can fill with additional information about your query

Edit on GitHub

Query Keys

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