Nested `createEntityAdapter` example

chatsSlice.ts

// Example of using multiple / nested `createEntityAdapter` calls within a single Redux Toolkit slice

interface Message {
  id: string;
  roomId: string;
  text: string;
  timestamp: string;
  username: string;
}

interface ChatRoomEntry {
  id: string;
  messages: EntityState<Message>;
}

const roomsAdapter = createEntityAdapter<ChatRoomEntry>();
const messagesAdapter = createEntityAdapter<Message>();

const fetchRooms = createAsyncThunk(
  "chats/fetchRooms",
  chatsAPI.fetchRooms
);

const fetchMessages = createAsyncThunk(
  "chats/fetchMessages",
  async (roomId) => {
    return chatsAPI.fetchMessages(roomId);
  }
)

const chatSlice = createSlice({
  name: "chats",
  initialState: roomsAdapter.getInitialState(),
  reducers: {
  
  },
  extraReducers: builder => {
    builder.addCase(fetchRooms.fulfilled, (state, action) => {
      const roomEntries = action.payload.map(room => {
        return {id: room.id, messages: messagesAdapter.getInitialState()};
      });
      
      roomsAdapter.setAll(state, roomEntries);
    })
    .addCase(fetchMessages.fulfilled, (state, action) => {
      const roomId = action.meta.arg;
      const roomEntry = state.entities[roomId];
      if (roomEntry) {
        messagesAdapter.setAll(roomEntry.messages, action.payload);
      }
    })
  }
})

/*
Resulting state:
{
  ids: ["chatRoom1"],
  entities: {
    chatRoom1: {
      id: "chatRoom1",
      messages: {
        ids: ["message1", "message2"],
        entities: {
          message1: {id: "message1", text: "hello"},
          message2: {id: "message2", text: "yo"},
        }
      }
    }
  }
}
*/

How do you make a selector for nested properties?
AFAIK, it'd be something like below

export const messagesByIdSelector = createSelector(
  curerntRoomSelector,
  (state: RootState, messageId: EntityId) => messageId,
  (room, messageId) => {
    const items = room?.messages;
    if (!items) {
      return;
    }

    const allMessages = messageEntities
      .getSelectors(() => items)
      .selectAll(() => items);

    return allMessages.find((item) => item.message_id === messageId);
  }
);

I achieved the expected data, but the const allMessages = messageEntitties .getSelectors(() => items) .selectAll(() => items); seems repeated many times.

Sorry for my ignorance, but I thought RTK encourages you to keep the state as flat as possible. We have a single API call that returns areaGroups, each with an array of areas. Our old Redux setup kept areas within areaGroups, but for RTK I was going down the path of separate areaGroups and areas entities.

const areaGroupsAdapter = createEntityAdapter();
const areasAdapter = createEntityAdapter();

const initialState = {
    areaGroups: areaGroupsAdapter.getInitialState(adapterInitialState),
    areas: areasAdapter.getInitialState(adapterInitialState)
};

export const entitiesSlice = createSlice({
    name: 'entities',
    initialState,
    reducers: {},
    extraReducers: builder => {
        builder.addCase(SET_AREA_GROUPS, (state, action) => {
            const { areaGroups, areas } = flattenAreaGroups(action.payload);
            
            areaGroupsAdapter.upsertMany(state.areaGroups, areaGroups);
            areasAdapter.upsertMany(state.areas, areas);
        });
});

flattenAreaGroups is a utility function that just extracts out the areas and assigns an areaGroupId property before returning each entity type.

My plan was to create a selector such as selectAllAreasByAreaGroupId.

Should I keep these entities nested?

(We're in the middle of migrating to RTK + Thunks so SET_AREA_GROUPS is some leftover Saga hooha BS that'll be converted.)

@rickysullivan-gallagher : yeah, "flat" is a generally good state design principle, but like everything it's not an absolute. It can depend on how you expect the state to get both accessed and updated. No hard rule here.

Thanks for the reply, @markerikson. In the words of the great 90s punk rock band, The Offspring, I'm going to Keep 'Em Separated. I like the idea of knowing that each entity has its own home and along with it, auto-generated selectors to boot. Thanks for all your awesome work.

So I decided that I'd try my hand with nesting slices. This way I can keep all my entities reducers/thunks/selectors etc under their own slice, yet keep a top level "entities" slice. But i'm stumped. I can dispatch the actions, and see them working. I just can't workout how to get the slice reducers to combine in the parent slice. https://stackblitz.com/~/github.com/rickysullivan-gallagher/vitejs-vite-ctk89t

@rickysullivan-gallagher I'm not actually sure what you're trying to do there, and this gist isn't a great place to provide support :) Could you drop by the #redux channel in the Reactiflux Discord ( https://www.reactiflux.com ) and ask there?

Will do @markerikson. I wasn't feeling confident this was the right place.