persistQueryClient (Experimental)

VERY IMPORTANT: This utility is currently in an experimental stage. This means that breaking changes will happen in minor AND patch releases. Use at your own risk. If you choose to rely on this in production in an experimental stage, please lock your version to a patch-level version to avoid unexpected breakages.

persistQueryClient is a utility for persisting the state of your queryClient and its caches for later use. Different persistors can be used to store your client and cache to many different storage layers.

Officially Supported Persistors

• createLocalStoragePersistor (Experimental)

Installation

This utility comes packaged with svelte-query and is available under the @sveltestack/svelte-query import.

Usage

Import the persistQueryClient function, and pass it your QueryClient instance (with a cacheTime set), and a Persistor interface (there are multiple persistor types you can use):

1 import { persistQueryClient } from '`@sveltestack/svelte-query`'
2 import { createLocalStoragePersistor } from '`@sveltestack/svelte-query`'
3 
4 const queryClient = new QueryClient({
5   defaultOptions: {
6     queries: {
7       cacheTime: 1000 * 60 * 60 * 24, // 24 hours
8     },
9   },
10 })
11 
12 const localStoragePersistor = createLocalStoragePersistor()
13 
14 persistQueryClient({
15   queryClient
16   persistor: localStoragePersistor,
17 })

IMPORTANT - for persist to work properly, you need to pass QueryClient a cacheTime value to override the default during hydration (as shown above).

If it is not set when creating the QueryClient instance, it will default to 300000 (5 minutes) for hydration, and the stored cache will be discarded after 5 minutes of inactivity. This is the default garbage collection behavior.

It should be set as the same value or higher than persistQueryClient's maxAge option. E.g. if maxAge is 24 hours (the default) then cacheTime should be 24 hours or higher. If lower than maxAge, garbage collection will kick in and discard the stored cache earlier than expected.

You can also pass it Infinity to disable garbage collection behavior entirely.

How does it work?

As you use your application:

• When your query/mutation cache is updated, it will be dehydrated and stored by the persistor you provided. By default, this action is throttled to happen at most every 1 second to save on potentially expensive writes to a persistor, but can be customized as you see fit.

When you reload/bootstrap your app:

• Attempts to load a previously persisted dehydrated query/mutation cache from the persistor
• If a cache is found that is older than the maxAge (which by default is 24 hours), it will be discarded. This can be customized as you see fit.

Cache Busting

Sometimes you may make changes to your application or data that immediately invalidate any and all cached data. If and when this happens, you can pass a buster string option to persistQueryClient, and if the cache that is found does not also have that buster string, it will be discarded.

 persistQueryClient({ queryClient, persistor, buster: buildHash })

API

persistQueryClient

Pass this function a QueryClient instance and a persistor that will persist your cache. Both are required

 persistQueryClient({ queryClient, persistor })

Options

An object of options:

1 interface PersistQueryClientOptions {
2   /** The QueryClient to persist */
3   queryClient: QueryClient
4   /** The Persistor interface for storing and restoring the cache
5    * to/from a persisted location */
6   persistor: Persistor
7   /** The max-allowed age of the cache.
8    * If a persisted cache is found that is older than this
9    * time, it will be discarded */
10   maxAge?: number
11   /** A unique string that can be used to forcefully
12    * invalidate existing caches if they do not share the same buster string */
13   buster?: string
14 }

The default options are:

1 {
2   maxAge = 1000 * 60 * 60 * 24, // 24 hours
3   buster = '',
4 }

Building a Persistor

Persistors have the following interface:

1 export interface Persistor {
2   persistClient(persistClient: PersistedClient): Promisable<void>
3   restoreClient(): Promisable<PersistedClient | undefined>
4   removeClient(): Promisable<void>
5 }

Persisted Client entries have the following interface:

1 export interface PersistedClient {
2   timestamp: number
3   buster: string
4   cacheState: any
5 }

Satisfy all of these interfaces and you've got yourself a persistor!