React-redux-cache NPM

react-redux-cache

Powerful yet lightweight data fetching and caching library that supports normalization unlike react-query and rtk-query, while having similar but very simple interface. Built on top of redux, fully typed and written on Typescript. Can be considered as ApolloClient for protocols other than GraphQL.

Normalization is the best way to keep the state of the app consistent between different views, reduces the number of fetches and allows to show cached data when navigating, which greatly improves user experience.

Remains full control of redux state with ability to write custom selectors, actions and reducers to manage cached state.

Usage example can be found in example/ folder and run by npm run example command from the root folder.

Installation

react, redux and react-redux are peer dependencies.

npm add react-redux-cache react redux react-redux

Initialization

The only function that needs to be imported is createCache, which creates fully typed reducer, hooks, actions, selectors and utils to be used in the app. All typenames, queries and mutations should be passed while initializing the cache for proper typing.

cache.ts

export const {
  reducer,
  hooks: {useClient, useMutation, useQuery, useSelectEntityById},
  // Actions, selectors and utils may be not used at all
  selectors: {entitiesSelector, entitiesByTypenameSelector},
  actions: {setQueryStateAndEntities, setMutationStateAndEntities, mergeEntityChanges},
  utils: {applyEntityChanges},
} = createCache({
  // This selector should return the cache state based on the path to its reducer.
  cacheStateSelector: (state) => state.cache,
  // Typenames provide a mapping of all typenames to their entity types, which is needed for normalization.
  // Empty objects with type casting can be used as values.
  typenames: {
    users: {} as User, // here `users` entities will have type `User`
    banks: {} as Bank,
  },
  queries: {
    getUsers: { query: getUsers },
    getUser: { query: getUser },
  },
  mutations: {
    updateUser: { mutation: updateUser },
    removeUser: { mutation: removeUser },
  },
})

store.ts

// Create store as usual, passing the new cache reducer
// under the key, previously used in cacheStateSelector
const store = configureStore({
  reducer: {
    cache: reducer,
  }
})

api.ts

Query result should be of type QueryResponse, mutation result should be of type MutationResponse. For normalization normalizr package is used in this example, but any other tool can be used if query result is of proper type. Perfect implementation is when the backend already returns normalized data.

// Example of query with normalization (recommended)

export const getUser = async (id: number) => {
  const result = await ...
  
  const normalizedResult: {
     // result is id of the user
    result: number
    // entities contain all normalized objects 
    entities: {
      users: Record<number, User>
      banks: Record<string, Bank>
    }
  } = normalize(result, getUserSchema)

  return normalizedResult
}

// Example of query without normalization (not recommended)

export const getBank = (id: string) => {
  const result: Bank = ...
  return {result} // result is bank object, no entities passed
}

// Example of mutation with normalization

export const removeUser = async (id: number) => {
  await ...
  return {
    remove: { users: [id] },
  }
}

Usage

UserScreen.tsx

export const UserScreen = () => {
  const {id} = useParams()

  // useQuery connects to redux state and if user with that id is already cached, fetch won't happen (with default cachePolicy 'cache-first')
  // Infers all types from created cache, telling here that params and result are of type `number`.
  const [{result: userId, loading, error}] = useQuery({
    query: 'getUser',
    params: Number(id),
  })

  const [updateUser, {loading: updatingUser}] = useMutation({
    mutation: 'updateUser',
  })

  // This selector is used for denormalization and returns entities with proper types - User and Bank
  const user = useSelectEntityById(userId, 'users')
  const bank = useSelectEntityById(user?.bankId, 'banks')

  if (loading) {
    return ...
  }

  return ...
}

Advanced

resultSelector

By default result of a query is stored under its cache key, but sometimes it makes sense to take result from other queries or normalized entities.

For example when single User entity is requested by userId for the first time, the entity can already be in the cache after getUsers query finished.

For that case resultSelector can be used:

// createCache

... = createCache({
  ...
  queries: {
    ...
    getUser: {
      query: getUser,
      resultSelector: (state, id) => state.entities.users[id]?.id, // <-- Result is selected from cached entities
    },
  },
})

// component

export const UserScreen = () => {
  ...

  // When screen mounts for the first time, query is not fetched
  // and cached value is returned if user entity was already in the cache
  const [{result, loading, error}] = useQuery({
    query: 'getUser',
    params: userId,
  })

  ...
}

Infinite scroll pagination

Here is an example of getUsers query configuration with pagination support. You can check full implementation in /example folder.

// createCache

...
} = createCache({
  ...
  queries: {
    getUsers: {
      query: getUsers,
      getCacheKey: () => 'all-pages', // single cache key is used for all pages
      mergeResults: (oldResult, {result: newResult}) => {
        if (!oldResult || newResult.page === 1) {
          return newResult
        }
        if (newResult.page === oldResult.page + 1) {
          return {
            ...newResult,
            items: [...oldResult.items, ...newResult.items],
          }
        }
        return oldResult
      },
    },
  },
  ...
})

// Component

export const GetUsersScreen = () => {
  const {query} = useClient()

  const [{result: usersResult, loading, error}, refetch] = useQuery({
    query: 'getUsers',
    params: 1 // page
  })

  const onLoadNextPage = () => {
    const lastLoadedPage = usersResult?.page ?? 0
    query({
      query: 'getUsers',
      params: lastLoadedPage + 1,
    })
  }

  const renderUser = (userId: number) => (
    <UserRow key={userId} userId={userId}>
  )

  ...

  return (
    <div>
      {usersResult?.items.map(renderUser)}
      <button onClick={refetch}>Refresh</button>
      <button onClick={onLoadNextPage}>Load next page</button>
    </div>
  )
}

redux-persist

Here is a simple redux-persist configuration:

// removes `loading` and `error` from persisted state
function stringifyReplacer(key: string, value: unknown) {
  return key === 'loading' || key === 'error' ? undefined : value
}

const persistedReducer = persistReducer(
  {
    key: 'cache',
    storage,
    whitelist: ['entities', 'queries'], // mutations are ignored
    throttle: 1000, // ms
    serialize: (value: unknown) => JSON.stringify(value, stringifyReplacer),
  },
  reducer
)

FAQ

What is cache key?

Cache key is used for storing the query state and for performing a fetch when it changes. Queries with the same cache key share their state.

Default implementation for getCacheKey is:

export const defaultGetCacheKey = <P = unknown>(params: P): Key => {
  switch (typeof params) {
    case 'string':
    case 'symbol':
      return params
    case 'object':
      return JSON.stringify(params)
    default:
      return String(params)
  }
}

It is recommended to override it when default implementation is not optimal or when keys in params object can be sorted in random order.

As example, can be overriden when implementing pagination.

react redux cache query normalization

@everything-registry/sub-chunk-2606

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