React Query Mønstre 2026: Data Fetching, Caching og Mutations med TanStack Query

TanStack Query er standardløsningen for server-tilstandsadministrasjon i React-applikasjoner.

useQuery: hente og cache data

useQuery abonnerer på en servertilstand med queryKey som cachenokkel.

import { useQuery, QueryClient, QueryClientProvider } from '@tanstack/react-query';

// Setup: wrap your app
const queryClient = new QueryClient({
    defaultOptions: {
        queries: {
            staleTime: 1000 * 60 * 5,  // 5 minutes
            gcTime: 1000 * 60 * 30,     // 30 minutes (formerly cacheTime)
            retry: 3,
            refetchOnWindowFocus: true,
        },
    },
});

function App() {
    return (
        <QueryClientProvider client={queryClient}>
            <MyApp />
        </QueryClientProvider>
    );
}

// Basic query
interface User {
    id: number;
    name: string;
    email: string;
}

function useUser(userId: number) {
    return useQuery<User>({
        queryKey: ['user', userId],      // cache key — must be unique
        queryFn: async () => {
            const res = await fetch(`/api/users/${userId}`);
            if (!res.ok) throw new Error('Failed to fetch user');
            return res.json();
        },
        enabled: userId > 0,            // only run if userId is valid
        staleTime: 1000 * 60 * 10,     // override global default
    });
}

function UserProfile({ userId }: { userId: number }) {
    const { data, isLoading, isError, error } = useUser(userId);

    if (isLoading) return <div>Loading...</div>;
    if (isError) return <div>Error: {error.message}</div>;

    return <div>{data.name} — {data.email}</div>;
}

useMutation: opprette, oppdatere, slette

useMutation håndterer CRUD-operasjoner med onSuccess-callbacks.

import { useMutation, useQueryClient } from '@tanstack/react-query';

interface CreatePostInput {
    title: string;
    body: string;
    userId: number;
}

function useCreatePost() {
    const queryClient = useQueryClient();

    return useMutation({
        mutationFn: async (input: CreatePostInput) => {
            const res = await fetch('/api/posts', {
                method: 'POST',
                headers: { 'Content-Type': 'application/json' },
                body: JSON.stringify(input),
            });
            if (!res.ok) throw new Error('Failed to create post');
            return res.json();
        },
        onSuccess: (newPost) => {
            // Invalidate and refetch posts list
            queryClient.invalidateQueries({ queryKey: ['posts'] });
            // Or add directly to cache (no refetch needed)
            queryClient.setQueryData(['post', newPost.id], newPost);
        },
        onError: (error) => {
            console.error('Failed to create post:', error);
        },
    });
}

function CreatePostForm() {
    const mutation = useCreatePost();

    const handleSubmit = (e: React.FormEvent) => {
        e.preventDefault();
        mutation.mutate({ title: 'New Post', body: 'Content', userId: 1 });
    };

    return (
        <form onSubmit={handleSubmit}>
            <button type="submit" disabled={mutation.isPending}>
                {mutation.isPending ? 'Creating...' : 'Create Post'}
            </button>
            {mutation.isError && <p>Error: {mutation.error.message}</p>}
            {mutation.isSuccess && <p>Post created!</p>}
        </form>
    );
}

Optimistiske oppdateringer for umiddelbar UI

Optimistiske oppdateringer bruker endringer før serversvaret.

import { useMutation, useQueryClient } from '@tanstack/react-query';

interface Todo {
    id: number;
    title: string;
    completed: boolean;
}

function useToggleTodo() {
    const queryClient = useQueryClient();

    return useMutation({
        mutationFn: (todo: Todo) =>
            fetch(`/api/todos/${todo.id}`, {
                method: 'PATCH',
                headers: { 'Content-Type': 'application/json' },
                body: JSON.stringify({ completed: !todo.completed }),
            }).then(r => r.json()),

        // Optimistic update — runs BEFORE the mutation
        onMutate: async (updatedTodo) => {
            // Cancel outgoing refetches
            await queryClient.cancelQueries({ queryKey: ['todos'] });

            // Snapshot current data for rollback
            const previousTodos = queryClient.getQueryData<Todo[]>(['todos']);

            // Optimistically update the cache
            queryClient.setQueryData<Todo[]>(['todos'], (old) =>
                old?.map(todo =>
                    todo.id === updatedTodo.id
                        ? { ...todo, completed: !todo.completed }
                        : todo
                )
            );

            return { previousTodos }; // context for onError
        },

        // If mutation fails, roll back to snapshot
        onError: (_err, _variables, context) => {
            if (context?.previousTodos) {
                queryClient.setQueryData(['todos'], context.previousTodos);
            }
        },

        // Always refetch after error or success
        onSettled: () => {
            queryClient.invalidateQueries({ queryKey: ['todos'] });
        },
    });
}

Uendelige spørringer for paginering

useInfiniteQuery håndterer markørbasert paginering.

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

interface Page {
    items: Post[];
    nextCursor?: string;
}

function useInfinitePosts() {
    return useInfiniteQuery<Page>({
        queryKey: ['posts', 'infinite'],
        queryFn: async ({ pageParam }) => {
            const url = pageParam
                ? `/api/posts?cursor=${pageParam}`
                : '/api/posts';
            return fetch(url).then(r => r.json());
        },
        initialPageParam: undefined as string | undefined,
        getNextPageParam: (lastPage) => lastPage.nextCursor,
    });
}

function InfinitePostList() {
    const {
        data,
        fetchNextPage,
        hasNextPage,
        isFetchingNextPage,
    } = useInfinitePosts();

    return (
        <div>
            {data?.pages.flatMap(page => page.items).map(post => (
                <div key={post.id}>{post.title}</div>
            ))}
            {hasNextPage && (
                <button onClick={() => fetchNextPage()} disabled={isFetchingNextPage}>
                    {isFetchingNextPage ? 'Loading...' : 'Load more'}
                </button>
            )}
        </div>
    );
}

Spørringsnokkelmønstre og forhåndshenting

Konsekvente nøkkelfabrikker forhindrer cache-konflikter.

// Query key patterns — factory functions for consistency
const queryKeys = {
    all: ['posts'] as const,
    lists: () => [...queryKeys.all, 'list'] as const,
    list: (filters: string) => [...queryKeys.lists(), { filters }] as const,
    details: () => [...queryKeys.all, 'detail'] as const,
    detail: (id: number) => [...queryKeys.details(), id] as const,
};

// Usage:
useQuery({ queryKey: queryKeys.detail(1), queryFn: ... });

// Invalidate all posts:
queryClient.invalidateQueries({ queryKey: queryKeys.all });

// Invalidate only lists:
queryClient.invalidateQueries({ queryKey: queryKeys.lists() });

// Prefetching for better UX
async function prefetchUser(userId: number) {
    await queryClient.prefetchQuery({
        queryKey: ['user', userId],
        queryFn: () => fetchUser(userId),
        staleTime: 10 * 60 * 1000, // only prefetch if > 10 min stale
    });
}

// On hover: prefetch before click
<link onMouseEnter={() => prefetchUser(userId)} href={`/users/${userId}`}>
    View Profile
</link>

TanStack Query vs andre løsninger

Beste praksis

• Bruke spørringsnokkel-fabrikker for konsistens.
• Angi staleTime basert på dataferskhetskrav.
• Alltid gi laste- og feiltilstander.
• Bruke optimistiske oppdateringer for raske handlinger.
• Forhåndshente data ved hover eller ruteøvergånger.

Ofte stilte spørsmål