id | title |
---|---|
paginated-queries |
Paginated / Lagged Queries |
Rendering paginated data is a very common UI pattern and in React Query, it "just works" by including the page information in the query key:
const result = useQuery(['projects', page], fetchProjects)
However, if you run this simple example, you might notice something strange:
The UI jumps in and out of the success
and loading
states because each new page is treated like a brand new query.
This experience is not optimal and unfortunately is how many tools today insist on working. But not React Query! As you may have guessed, React Query comes with an awesome featured called keepPreviousData
that allows us to get around this.
Consider the following example where we would ideally want to increment a pageIndex (or cursor) for a query. If we were to use useQuery
, it would still technically work fine, but the UI would jump in and out of the success
and loading
states as different queries are created and destroyed for each page or cursor. By setting keepPreviousData
to true
we get a few new things:
- The data from the last successful fetch available while new data is being requested, even though the query key has changed.
- When the new data arrives, the previous
data
is seamlessly swapped to show the new data. isPreviousData
is made available to know what data the query is currently providing you
function Todos() {
const [page, setPage] = React.useState(0)
const fetchProjects = (page = 0) => fetch('/api/projects?page=' + page)
const {
isLoading,
isError,
error,
data,
isFetching,
isPreviousData,
} = useQuery(['projects', page], () => fetchProjects(page))
return (
<div>
{isLoading ? (
<div>Loading...</div>
) : isError ? (
<div>Error: {error.message}</div>
) : (
<div>
{data.projects.map(project => (
<p key={project.id}>{project.name}</p>
))}
</div>
)}
<span>Current Page: {page + 1}</span>
<button
onClick={() => setPage(old => Math.max(old - 1, 0))}
disabled={page === 0}
>
Previous Page
</button>{' '}
<button
onClick={() => {
if (!isPreviousData && data.hasMore) {
setPage(old => old + 1)
}
}}
// Disable the Next Page button until we know a next page is available
disabled={isPreviousData || !data.hasMore}
>
Next Page
</button>
{isFetching ? <span> Loading...</span> : null}{' '}
</div>
)
}
While not as common, the keepPreviousData
option also works flawlessly with the useInfiniteQuery
hook, so you can seamlessly allow your users to continue to see cached data while infinite query keys change over time.