Placeholder Query Data - Query

tsx

function Todos() {
  const todosQuery = useQuery(() => ({
    queryKey: ['todos'],
    queryFn: () => fetch('/todos'),
    placeholderData: placeholderTodos,
  }))
}

Placeholder Data Memoization

If the process for accessing a query's placeholder data is intensive or just not something you want to perform on every render, you can memoize the value:

tsx

function Todos() {
  const placeholderData = createMemo(() => generateFakeTodos())
  const todosQuery = useQuery(() => ({
    queryKey: ['todos'],
    queryFn: () => fetch('/todos'),
    placeholderData: placeholderData(),
  }))
}

tsx

const todosQuery = useQuery(() => ({
  queryKey: ['todos', id],
  queryFn: () => fetch(`/todos/${id}`),
  placeholderData: (previousData, previousQuery) => previousData,
}))

tsx

function BlogPost(props) {
  const queryClient = useQueryClient()
  const blogPostQuery = useQuery(() => ({
    queryKey: ['blogPost', props.blogPostId],
    queryFn: () => fetch(`/blogPosts/${props.blogPostId}`),
    placeholderData: () => {
      // Use the smaller/preview version of the blogPost from the 'blogPosts'
      // query as the placeholder data for this blogPost query
      return queryClient
        .getQueryData(['blogPosts'])
        ?.find((d) => d.id === props.blogPostId)
    },
  }))
}