feat: query cache provider

the query cache now comes from a context, meaning users can easily override and control the cache being used inside their application

README.md

@@ -313,8 +313,10 @@ This library is being built and maintained by me, @tannerlinsley and I am always
   - [`queryCache.isFetching`](#querycacheisfetching)
   - [`queryCache.subscribe`](#querycachesubscribe)
   - [`queryCache.clear`](#querycacheclear)
+  - [`useQueryCache`](#usequerycache)
   - [`useIsFetching`](#useisfetching)
   - [`ReactQueryConfigProvider`](#reactqueryconfigprovider)
+  - [`ReactQueryCacheProvider`](#reactquerycacheprovider)
   - [`setConsole`](#setconsole)
 - [Contributors ✨](#contributors-)
 
@@ -2548,6 +2550,18 @@ queryCache.clear()
 - `queries: Array<Query>`
   - This will be an array containing the queries that were found.
 
+## `useQueryCache`
+
+The `useQueryCache` hook returns the current queryCache instance.
+
+```js
+import { useQueryCache } from 'react-query';
+
+const queryCache = useQueryCache()
+```
+
+If you are using the `ReactQueryCacheProvider` to set a custom cache, you cannot simply import `{ queryCache }` any more. This hook will ensure you're getting the correct instance.
+
 ## `useIsFetching`
 
 `useIsFetching` is an optional hook that returns the `number` of the queries that your application is loading or fetching in the background (useful for app-wide loading indicators).
@@ -2608,6 +2622,29 @@ function App() {
   - Must be **stable** or **memoized**. Do not create an inline object!
   - For non-global properties please see their usage in both the [`useQuery` hook](#usequery) and the [`useMutation` hook](#usemutation).
 
+## `ReactQueryCacheProvider`
+
+`ReactQueryCacheProvider` is an optional provider component for explicitly setting the query cache used by `useQuery`. This is useful for creating component-level caches that are not completely global, as well as making truly isolated unit tests.
+
+```js
+import { ReactQueryCacheProvider, makeQueryCache } from 'react-query';
+
+const queryCache = makeQueryCache()
+
+function App() {
+  return (
+    <ReactQueryCacheProvider queryCache={queryCache}>
+      ...
+    </ReactQueryCacheProvider>
+  )
+}
+```
+
+### Options
+- `queryCache: Object`
+  - In instance of queryCache, you can use the `makeQueryCache` factory to create this.
+  - If not provided, a new cache will be generated.
+
 ## `setConsole`
 
 `setConsole` is an optional utility function that allows you to replace the `console` interface used to log errors. By default, the `window.console` object is used. If no global `console` object is found in the environment, nothing will be logged.

src/index.js

@@ -1,4 +1,9 @@
-export { queryCache } from './queryCache'
+export {
+  queryCache,
+  makeQueryCache,
+  ReactQueryCacheProvider,
+  useQueryCache,
+} from './queryCache'
 export { ReactQueryConfigProvider } from './config'
 export { setFocusHandler } from './setFocusHandler'
 export { useIsFetching } from './useIsFetching'

src/index.production.js

@@ -1,4 +1,9 @@
-export { queryCache } from './queryCache'
+export {
+  queryCache,
+  makeQueryCache,
+  ReactQueryCacheProvider,
+  useQueryCache,
+} from './queryCache'
 export { ReactQueryConfigProvider } from './config'
 export { setFocusHandler } from './setFocusHandler'
 export { useIsFetching } from './useIsFetching'

src/queryCache.js

@@ -1,3 +1,4 @@
+import React from 'react'
 import {
   isServer,
   functionalUpdate,
@@ -14,6 +15,20 @@ import { defaultConfigRef } from './config'
 
 export const queryCache = makeQueryCache()
 
+export const queryCacheContext = React.createContext(queryCache)
+
+export function useQueryCache() {
+  return React.useContext(queryCacheContext)
+}
+
+export function ReactQueryCacheProvider({ queryCache, children }) {
+  return (
+    <queryCacheContext.Provider value={queryCache || makeQueryCache()}>
+      {children}
+    </queryCacheContext.Provider>
+  )
+}
+
 const actionInit = {}
 const actionFailed = {}
 const actionMarkStale = {}
@@ -32,7 +47,7 @@ export function makeQueryCache() {
   }
 
   const notifyGlobalListeners = () => {
-    cache.isFetching = Object.values(queryCache.queries).reduce(
+    cache.isFetching = Object.values(cache.queries).reduce(
       (acc, query) => (query.state.isFetching ? acc + 1 : acc),
       0
     )
@@ -113,6 +128,7 @@ export function makeQueryCache() {
       query.config = { ...query.config, ...config }
     } else {
       query = makeQuery({
+        cache,
         queryKey,
         queryHash,
         queryVariables,
@@ -196,6 +212,7 @@ export function makeQueryCache() {
   }
 
   function makeQuery(options) {
+    const queryCache = options.cache
     const reducer = options.config.queryReducer || defaultQueryReducer
 
     const noQueryHash = typeof options.queryHash === 'undefined'

src/useBaseQuery.js

@@ -2,7 +2,7 @@ import React from 'react'
 
 //
 
-import { queryCache } from './queryCache'
+import { useQueryCache } from './queryCache'
 import { useConfigContext } from './config'
 import {
   useUid,
@@ -20,6 +20,8 @@ export function useBaseQuery(queryKey, queryVariables, queryFn, config = {}) {
     ...config,
   }
 
+  const queryCache = useQueryCache()
+
   const queryRef = React.useRef()
 
   const newQuery = queryCache._buildQuery(

src/useIsFetching.js

@@ -1,8 +1,9 @@
 import React from 'react'
 
-import { queryCache } from './queryCache'
+import { useQueryCache } from './queryCache'
 
 export function useIsFetching() {
+  const queryCache = useQueryCache()
   const [state, setState] = React.useState({})
 
   React.useEffect(() => {

types/index.d.ts

@@ -699,6 +699,20 @@ export interface QueryCache {
 
 export const queryCache: QueryCache
 
+/**
+ * a factory that creates a new query cache
+ */
+export function makeQueryCache(): QueryCache
+
+/**
+ * A hook that uses the query cache context
+ */
+export function useQueryCache(): QueryCache
+
+export const ReactQueryCacheProvider: React.ComponentType<{
+  queryCache?: QueryCache
+}>
+
 /**
  * A hook that returns the number of the quiries that your application is loading or fetching in the background
  * (useful for app-wide loading indicators).