RTK Query cache utils. Useful abstractions for creating `provides`/`invalidates` cache data tags against endpoints.

rtkQueryCacheUtils.ts

import { FetchBaseQueryError } from '@rtk-incubator/rtk-query/dist';

/**
 * Default tags used by the cacher helpers
 */
const defaultTags = ["UNAUTHORIZED", "UNKNOWN_ERROR"] as const;
type DefaultTags = typeof defaultTags[number];

function concatErrorCache<T, ID>(
  existingCache: CacheList<T, ID>,
  error: FetchBaseQueryError | undefined
): CacheList<T, ID> {
  if (error && "status" in error && error.status === 401) {
    // unauthorized error
    return [...existingCache, "UNAUTHORIZED"];
  }

  // unknown error
  return [...existingCache, "UNKNOWN_ERROR"];
}

/**
 * An individual cache item
 */
export type CacheItem<T, ID> = { type: T; id: ID };

/**
 * A list of cache items, including a LIST entity cache
 */
export type CacheList<T, ID> = (
  | CacheItem<T, "LIST">
  | CacheItem<T, ID>
  | DefaultTags
)[];

/**
 * Inner function returned by `providesList` to be passed to the `provides` property of a query
 */
type InnerProvidesList<T> = <
  Results extends { id: unknown }[],
  Error extends FetchBaseQueryError
>(
  results: Results | undefined,
  error: Error | undefined
) => CacheList<T, Results[number]["id"]>;

/**
 * HOF to create an entity cache to provide a LIST,
 * depending on the results being in a common format.
 *
 * Will not provide individual items without a result.
 *
 * @example
 * ```ts
 * const results = [
 *   { id: 1, message: 'foo' },
 *   { id: 2, message: 'bar' }
 * ]
 * providesList('Todo')(results)
 * // [
 * //   { type: 'Todo', id: 'List'},
 * //   { type: 'Todo', id: 1 },
 * //   { type: 'Todo', id: 2 },
 * // ]
 * ```
 */
export const providesList = <T extends string>(
  type: T
): InnerProvidesList<T> => (results, error) => {
  // is result available?
  if (results) {
    // successful query
    return [
      { type, id: "LIST" },
      ...results.map(({ id }) => ({ type, id } as const))
    ];
  }
  // Received an error, include an error cache item to the cache list
  return concatErrorCache([{ type, id: "LIST" }], error);
};

/**
 * HOF to create an entity cache to invalidate a LIST.
 *
 * Invalidates regardless of result.
 *
 * @example
 * ```ts
 * invalidatesList('Todo')()
 * // [{ type: 'Todo', id: 'List' }]
 * ```
 */
export const invalidatesList = <T extends string>(type: T) => (): readonly [
  CacheItem<T, "LIST">
] => [{ type, id: "LIST" }] as const;


type InnerProvidesNestedList<T> = <
  Results extends { data: { id: unknown }[] },
  Error extends FetchBaseQueryError
>(
  results: Results | undefined,
  error: Error | undefined
) => CacheList<T, Results["data"][number]["id"]>;

/**
 * Similar to `providesList`, but for data located at a nested property,
 * e.g. `results.data` in a paginated response.
 * The property is hard coded, so re-create a version of this function based
 * on a data shape your API returns for best results.
 */
export const providesNestedList = <T extends string>(
  type: T
): InnerProvidesNestedList<T> => (results, error) => {
  // is result available?
  if (results) {
    // successful query
    return [
      { type, id: "LIST" },
      ...results.data.map(({ id }) => ({ type, id } as const))
    ];
  }
  // Received an error, include an error cache item to the cache list
  return concatErrorCache([{ type, id: "LIST" }], error);
};


/**
 * HOF to create an entity cache for a single item using the query argument as the ID.
 *
 * @example
 * ```ts
 * cacheByIdArg('Todo')({ id: 5, message: 'walk the fish' }, undefined, 5)
 * // returns:
 * // [{ type: 'Todo', id: 5 }]
 * ```
 */
export const cacheByIdArg = <T extends string>(type: T) => <
  ID,
  Result = undefined,
  Error = undefined
>(
  result: Result,
  error: Error,
  id: ID
): readonly [CacheItem<T, ID>] => [{ type, id }] as const;

/**
 * HOF to create an entity cache for a single item using the id property from the query argument as the ID.
 *
 * @example
 * ```ts
 * cacheByIdArgProperty('Todo')(undefined, { id: 5, message: 'sweep up' })
 * // returns:
 * // [{ type: 'Todo', id: 5 }]
 * ```
 */
export const cacheByIdArgProperty = <T extends string>(type: T) => <
  Arg extends { id: unknown },
  Result = undefined,
  Error = undefined
>(
  result: Result,
  error: Error,
  arg: Arg
): readonly [CacheItem<T, Arg["id"]>] | [] => [{ type, id: arg.id }] as const;

/**
 * HOF to invalidate the 'UNAUTHORIZED' type cache item.
 */
export const invalidatesUnauthorized = () => <
  Arg = undefined,
  Result = undefined,
  Error = undefined
>(
  result: Result,
  error: Error,
  arg: Arg
): ["UNAUTHORIZED"] => ["UNAUTHORIZED"];

/**
 * HOF to invalidate the 'UNKNOWN_ERROR' type cache item.
 */
export const invalidatesUnknownErrors = () => <
  Arg = undefined,
  Result = undefined,
  Error = undefined
>(
  result: Result,
  error: Error,
  arg: Arg
): ["UNKNOWN_ERROR"] => ["UNKNOWN_ERROR"];

/**
 * Utility helpers for common provides/invalidates scenarios
 */
export const cacher = {
  defaultTags,
  providesList,
  invalidatesList,
  providesNestedList,
  cacheByIdArg,
  cacheByIdArgProperty,
  invalidatesUnauthorized,
  invalidatesUnknownErrors
};

I've read the conversation between @troypoulter and @Shrugsy about providesNestedList and InnerProvidesNestedList which is very convenient with REST APIs.

But, in my case, the paginated API responds the data according to the request. I mean:

If I request getUsers, the API responds:

{
      totalCount: number;
      totalPage: number;
      currentPage: number;
      users: User[];    // <--------- here is users, not data !
}

If I request getAuthusers, the API responds:

{
      totalCount: number;
      totalPage: number;
      currentPage: number;
      authusers: Authuser[];    // <--------- here is authusers, not data !
}

If I request getBooks, the API responds:

{
      totalCount: number;
      totalPage: number;
      currentPage: number;
      books: Book[];    // <--------- here is books, not data !
}

and so forth.

In this case I suppose, I have to add another parameter (relevant key string) into providesNestedList in order to read it from response through response[key], because it is not always response.data; which could be response.users, or response.authusers or response.books etc.

// for the getUsers endpoint
providesTags: cacher.providesNestedList("User", "users");

// for the getAuthusers endpoint
providesTags: cacher.providesNestedList("Authuser", "authusers");

// for the getBooks endpoint
providesTags: cacher.providesNestedList("Book", "books");

But I don't know how to pass the parameter key into ** InnerProvidesNestedList** in order to provide type inference for the type Results.

type InnerProvidesNestedList<T> = <
  Results extends { data: { id: unknown }[] },   // <---- it is not always data any more, could be users, authusers, books or could be data in the case of @troypoulter as well !!
  Error extends FetchBaseQueryError
>(
  results: Results | undefined,
  error: Error | undefined
) => CacheList<T, Results["data"][number]["id"]>;  // <---- and here, the key is not always "data" !

If we re-arrange providesNestedList and InnerProvidesNestedList, this two functions could be more generic, and I need this for my case indeed.

@talatkuyuk

Possible solution you could use for a dynamic key in a nested list

type InnerProvidesNestedList<T, K extends string> = <
  Results extends { [Key in K]: { id: unknown }[] },
  Error extends FetchBaseQueryError
>(
  results: Results | undefined,
  error: Error | undefined
) => CacheList<T, Results[K][number]['id']>;

/**
 * Similar to `providesList`, but for data located at a nested property,
 * e.g. `results.data` in a paginated response.
 * The property is hard coded, so re-create a version of this function based
 * on a data shape your API returns for best results.
 */
export const providesNestedList =
  <T extends string, K extends string>(type: T, key: K): InnerProvidesNestedList<T, K> =>
  (results, error) => {
    // is result available?
    if (results) {
      // successful query
      return [
        { type, id: 'LIST' },
        ...results[key].map(({ id }) => ({ type, id } as const)),
      ];
    }
    // Received an error, include an error cache item to the cache list
    return concatErrorCache([{ type, id: 'LIST' }], error);
  };

// for the getUsers endpoint
providesTags: cacher.providesNestedList("User", "users");

// for the getAuthusers endpoint
providesTags: cacher.providesNestedList("Authuser", "authusers");

// for the getBooks endpoint
providesTags: cacher.providesNestedList("Book", "books");

Thank you @hrafnkellbaldurs, it has worked.

Now, the cacher utility is available for the server responses having the actual records/list in a "dynamic key" rather than hard-coded "data" key.

My recommendation to other developers is to keep the function providesNestedList and the type InnerProvidesNestedList as it is and to add the new function asprovidesNestedDynamicList and the new type as InnerProvidesNestedDynamicList which @hrafnkellbaldurs has provided in order to have flexibility.

Thanks again.