# Infinite Queries

Rendering lists that can additively "load more" data onto an existing set of data or "infinite scroll" is also a very common UI pattern. TanStack Query supports a useful version of `useQuery` called `useInfiniteQuery` for querying these types of lists.

When using `useInfiniteQuery`, you'll notice a few things are different:

- `data` is now an object containing infinite query data:
- `data.pages` array containing the fetched pages
- `data.pageParams` array containing the page params used to fetch the pages
- The `fetchNextPage` and `fetchPreviousPage` functions are now available
- The `getNextPageParam` and `getPreviousPageParam` options are available for both determining if there is more data to load and the information to fetch it. This information is supplied as an additional parameter in the query function (which can optionally be overridden when calling the `fetchNextPage` or `fetchPreviousPage` functions)
- A `hasNextPage` boolean is now available and is `true` if `getNextPageParam` returns a value other than `undefined`
- A `hasPreviousPage` boolean is now available and is `true` if `getPreviousPageParam` returns a value other than `undefined`
- The `isFetchingNextPage` and `isFetchingPreviousPage` booleans are now available to distinguish between a background refresh state and a loading more state

> Note: When using options like `initialData` or `select` in your query, make sure that when you restructure your data that it still includes `data.pages` and `data.pageParams` properties, otherwise your changes will be overwritten by the query in its return!

## Example

Let's assume we have an API that returns pages of `projects` 3 at a time based on a `cursor` index along with a cursor that can be used to fetch the next group of projects:

```tsx
fetch('/api/projects?cursor=0')
// { data: [...], nextCursor: 3}
fetch('/api/projects?cursor=3')
// { data: [...], nextCursor: 6}
fetch('/api/projects?cursor=6')
// { data: [...], nextCursor: 9}
fetch('/api/projects?cursor=9')
// { data: [...] }
```

With this information, we can create a "Load More" UI by:

- Waiting for `useInfiniteQuery` to request the first group of data by default
- Returning the information for the next query in `getNextPageParam`
- Calling `fetchNextPage` function

> Note: It's very important you do not call `fetchNextPage` with arguments unless you want them to override the `pageParam` data returned from the `getNextPageParam` function. e.g. Do not do this: `<button onClick={fetchNextPage} />` as this would send the onClick event to the `fetchNextPage` function.

[//]: # 'Example'

```tsx
import { useInfiniteQuery } from '@tanstack/react-query'

function Projects() {
  const fetchProjects = async ({ pageParam = 0 }) => {
    const res = await fetch('/api/projects?cursor=' + pageParam)
    return res.json()
  }

  const {
    data,
    error,
    fetchNextPage,
    hasNextPage,
    isFetching,
    isFetchingNextPage,
    status,
  } = useInfiniteQuery({
    queryKey: ['projects'],
    queryFn: fetchProjects,
    getNextPageParam: (lastPage, pages) => lastPage.nextCursor,
  })

  return status === 'loading' ? (
    <p>Loading...</p>
  ) : status === 'error' ? (
    <p>Error: {error.message}</p>
  ) : (
    <>
      {data.pages.map((group, i) => (
        <React.Fragment key={i}>
          {group.data.map((project) => (
            <p key={project.id}>{project.name}</p>
          ))}
        </React.Fragment>
      ))}
      <div>
        <button
          onClick={() => fetchNextPage()}
          disabled={!hasNextPage || isFetchingNextPage}
        >
          {isFetchingNextPage
            ? 'Loading more...'
            : hasNextPage
              ? 'Load More'
              : 'Nothing more to load'}
        </button>
      </div>
      <div>{isFetching && !isFetchingNextPage ? 'Fetching...' : null}</div>
    </>
  )
}
```

[//]: # 'Example'

It's essential to understand that calling `fetchNextPage` while an ongoing fetch is in progress runs the risk of overwriting data refreshes happening in the background. This situation becomes particularly critical when rendering a list and triggering `fetchNextPage` simultaneously.

Remember, there can only be a single ongoing fetch for an InfiniteQuery. A single cache entry is shared for all pages, attempting to fetch twice simultaneously might lead to data overwrites.

If you intend to enable simultaneous fetching, you can utilize the `{ cancelRefetch: false }` option (default: true) within `fetchNextPage`.

To ensure a seamless querying process without conflicts, it's highly recommended to verify that the query is not in an `isFetching` state, especially if the user won't directly control that call.

[//]: # 'Example1'

```jsx
<List onEndReached={() => !isFetching && fetchNextPage()} />
```

[//]: # 'Example1'

## What happens when an infinite query needs to be refetched?

When an infinite query becomes `stale` and needs to be refetched, each group is fetched `sequentially`, starting from the first one. This ensures that even if the underlying data is mutated, we're not using stale cursors and potentially getting duplicates or skipping records. If an infinite query's results are ever removed from the queryCache, the pagination restarts at the initial state with only the initial group being requested.

### refetchPage

If you only want to actively refetch a subset of all pages, you can pass the `refetchPage` function to `refetch` returned from `useInfiniteQuery`.

[//]: # 'Example2'

```tsx
const { refetch } = useInfiniteQuery({
  queryKey: ['projects'],
  queryFn: fetchProjects,
  getNextPageParam: (lastPage, pages) => lastPage.nextCursor,
})

// only refetch the first page
refetch({ refetchPage: (page, index) => index === 0 })
```

[//]: # 'Example2'

You can also pass this function as part of the 2nd argument (`queryFilters`) to [queryClient.refetchQueries](../../../../reference/QueryClient#queryclientrefetchqueries), [queryClient.invalidateQueries](../../../../reference/QueryClient#queryclientinvalidatequeries) or [queryClient.resetQueries](../../../../reference/QueryClient#queryclientresetqueries).

**Signature**

- `refetchPage: (page: TData, index: number, allPages: TData[]) => boolean`

The function is executed for each page, and only pages where this function returns `true` will be refetched.

## What if I need to pass custom information to my query function?

By default, the variable returned from `getNextPageParam` will be supplied to the query function, but in some cases, you may want to override this. You can pass custom variables to the `fetchNextPage` function which will override the default variable like so:

[//]: # 'Example3'

```tsx
function Projects() {
  const fetchProjects = ({ pageParam = 0 }) =>
    fetch('/api/projects?cursor=' + pageParam)

  const {
    status,
    data,
    isFetching,
    isFetchingNextPage,
    fetchNextPage,
    hasNextPage,
  } = useInfiniteQuery({
    queryKey: ['projects'],
    queryFn: fetchProjects,
    getNextPageParam: (lastPage, pages) => lastPage.nextCursor,
  })

  // Pass your own page param
  const skipToCursor50 = () => fetchNextPage({ pageParam: 50 })
}
```

[//]: # 'Example3'

## What if I want to implement a bi-directional infinite list?

Bi-directional lists can be implemented by using the `getPreviousPageParam`, `fetchPreviousPage`, `hasPreviousPage` and `isFetchingPreviousPage` properties and functions.

[//]: # 'Example4'

```tsx
useInfiniteQuery({
  queryKey: ['projects'],
  queryFn: fetchProjects,
  getNextPageParam: (lastPage, pages) => lastPage.nextCursor,
  getPreviousPageParam: (firstPage, pages) => firstPage.prevCursor,
})
```

[//]: # 'Example4'

## What if I want to show the pages in reversed order?

Sometimes you may want to show the pages in reversed order. If this is case, you can use the `select` option:

[//]: # 'Example5'

```tsx
useInfiniteQuery({
  queryKey: ['projects'],
  queryFn: fetchProjects,
  select: (data) => ({
    pages: [...data.pages].reverse(),
    pageParams: [...data.pageParams].reverse(),
  }),
})
```

[//]: # 'Example5'

## What if I want to manually update the infinite query?

### Manually removing first page:

[//]: # 'Example6'

```tsx
queryClient.setQueryData(['projects'], (data) => ({
  pages: data.pages.slice(1),
  pageParams: data.pageParams.slice(1),
}))
```

[//]: # 'Example6'

### Manually removing a single value from an individual page:

[//]: # 'Example7'

```tsx
const newPagesArray =
  oldPagesArray?.pages.map((page) =>
    page.filter((val) => val.id !== updatedId),
  ) ?? []

queryClient.setQueryData(['projects'], (data) => ({
  pages: newPagesArray,
  pageParams: data.pageParams,
}))
```

[//]: # 'Example7'

### Keep only the first page:

[//]: # 'Example8'

```tsx
queryClient.setQueryData(['projects'], (data) => ({
  pages: data.pages.slice(0, 1),
  pageParams: data.pageParams.slice(0, 1),
}))
```

[//]: # 'Example8'

Make sure to always keep the same data structure of pages and pageParams!