data-fetching-architecture

LobeHub Data Fetching Architecture

Related: store-data-structures covers List vs Detail data shape rationale (Map vs Array).

Architecture Overview

┌─────────────┐
│  Component  │
└──────┬──────┘
       │ 1. Call useFetchXxx hook from store
       ↓
┌──────────────────┐
│  Zustand Store   │
│  (State + Hook)  │
└──────┬───────────┘
       │ 2. useClientDataSWR calls service
       ↓
┌──────────────────┐
│  Service Layer   │
│  (xxxService)    │
└──────┬───────────┘
       │ 3. Call lambdaClient
       ↓
┌──────────────────┐
│  lambdaClient    │
│  (TRPC Client)   │
└──────────────────┘

Core Principles

✅ DO

1. Use Service Layer for all API calls
2. Use Store SWR Hooks for data fetching (not useEffect)
3. Use proper data structures — see store-data-structures skill for List vs Detail patterns
4. Use lambdaClient.mutate for write operations (create/update/delete)
5. Use lambdaClient.query only inside service methods
6. Naming convention — read hooks are useFetchXxx, cache invalidation helpers are refreshXxx (e.g. useFetchBenchmarks / refreshBenchmarks). Mutations then chain refreshXxx() after the service call.

❌ DON'T

1. Never use useEffect for data fetching
2. Never call lambdaClient directly in components or stores
3. Never use useState for server data
4. Never mix data structure patterns — follow store-data-structures skill

Layer 1: Service Layer

Purpose

• Encapsulate all API calls to lambdaClient
• Provide clean, typed interfaces
• Single source of truth for API operations

Service Structure

// src/services/agentEval.ts
class AgentEvalService {
  // Query methods - READ operations
  async listBenchmarks() {
    return lambdaClient.agentEval.listBenchmarks.query();
  }

  async getBenchmark(id: string) {
    return lambdaClient.agentEval.getBenchmark.query({ id });
  }

  // Mutation methods - WRITE operations
  async createBenchmark(params: CreateBenchmarkParams) {
    return lambdaClient.agentEval.createBenchmark.mutate(params);
  }

  async updateBenchmark(params: UpdateBenchmarkParams) {
    return lambdaClient.agentEval.updateBenchmark.mutate(params);
  }

  async deleteBenchmark(id: string) {
    return lambdaClient.agentEval.deleteBenchmark.mutate({ id });
  }
}

export const agentEvalService = new AgentEvalService();

Service Guidelines

1. One service per domain (e.g., agentEval, ragEval, aiAgent)
2. Export singleton instance (export const xxxService = new XxxService())
3. Method names match operations (list, get, create, update, delete)
4. Clear parameter types (use interfaces for complex params)

Layer 2: Store with SWR Hooks

Purpose

• Manage client-side state
• Provide SWR hooks for data fetching
• Handle cache invalidation

State Structure

// src/store/eval/slices/benchmark/initialState.ts
export interface BenchmarkSliceState {
  // List data - simple array
  benchmarkList: AgentEvalBenchmarkListItem[];
  benchmarkListInit: boolean;

  // Detail data - map for caching
  benchmarkDetailMap: Record<string, AgentEvalBenchmark>;
  loadingBenchmarkDetailIds: string[];

  // Mutation states
  isCreatingBenchmark: boolean;
  isUpdatingBenchmark: boolean;
  isDeletingBenchmark: boolean;
}

For complete initialState, reducer, and internal dispatch patterns, see the store-data-structures skill.

Actions

// src/store/eval/slices/benchmark/action.ts
const FETCH_BENCHMARKS_KEY = 'FETCH_BENCHMARKS';
const FETCH_BENCHMARK_DETAIL_KEY = 'FETCH_BENCHMARK_DETAIL';

export interface BenchmarkAction {
  // SWR Hooks - for data fetching
  useFetchBenchmarks: () => SWRResponse;
  useFetchBenchmarkDetail: (id?: string) => SWRResponse;

  // Refresh methods - for cache invalidation
  refreshBenchmarks: () => Promise<void>;
  refreshBenchmarkDetail: (id: string) => Promise<void>;

  // Mutation actions
  createBenchmark: (params: CreateParams) => Promise<any>;
  updateBenchmark: (params: UpdateParams) => Promise<void>;
  deleteBenchmark: (id: string) => Promise<void>;

  // Internal methods - not for direct UI use
  internal_dispatchBenchmarkDetail: (payload: BenchmarkDetailDispatch) => void;
  internal_updateBenchmarkDetailLoading: (id: string, loading: boolean) => void;
}

export const createBenchmarkSlice: StateCreator<EvalStore, any, [], BenchmarkAction> = (
  set,
  get,
) => ({
  // Fetch list — simple array stored in benchmarkList
  useFetchBenchmarks: () =>
    useClientDataSWR(FETCH_BENCHMARKS_KEY, () => agentEvalService.listBenchmarks(), {
      onSuccess: (data) => {
        set({ benchmarkList: data, benchmarkListInit: true }, false, 'useFetchBenchmarks/success');
      },
    }),

  // Fetch detail — null key disables the request when id is missing
  useFetchBenchmarkDetail: (id) =>
    useClientDataSWR(
      id ? [FETCH_BENCHMARK_DETAIL_KEY, id] : null,
      () => agentEvalService.getBenchmark(id!),
      {
        onSuccess: (data) => {
          get().internal_dispatchBenchmarkDetail({
            type: 'setBenchmarkDetail',
            id: id!,
            value: data,
          });
          get().internal_updateBenchmarkDetailLoading(id!, false);
        },
      },
    ),

  // Refresh methods
  refreshBenchmarks: () => mutate(FETCH_BENCHMARKS_KEY),
  refreshBenchmarkDetail: (id) => mutate([FETCH_BENCHMARK_DETAIL_KEY, id]),

  // CREATE — refresh list after creation
  createBenchmark: async (params) => {
    set({ isCreatingBenchmark: true }, false, 'createBenchmark/start');
    try {
      const result = await agentEvalService.createBenchmark(params);
      await get().refreshBenchmarks();
      return result;
    } finally {
      set({ isCreatingBenchmark: false }, false, 'createBenchmark/end');
    }
  },

  // UPDATE — optimistic update + refresh
  updateBenchmark: async (params) => {
    const { id } = params;

    // 1. Optimistic update
    get().internal_dispatchBenchmarkDetail({
      type: 'updateBenchmarkDetail',
      id,
      value: params,
    });
    // 2. Set loading
    get().internal_updateBenchmarkDetailLoading(id, true);

    try {
      // 3. Call service
      await agentEvalService.updateBenchmark(params);
      // 4. Refresh from server
      await get().refreshBenchmarks();
      await get().refreshBenchmarkDetail(id);
    } finally {
      get().internal_updateBenchmarkDetailLoading(id, false);
    }
  },

  // DELETE — optimistic update + refresh
  deleteBenchmark: async (id) => {
    get().internal_dispatchBenchmarkDetail({ type: 'deleteBenchmarkDetail', id });
    get().internal_updateBenchmarkDetailLoading(id, true);

    try {
      await agentEvalService.deleteBenchmark(id);
      await get().refreshBenchmarks();
    } finally {
      get().internal_updateBenchmarkDetailLoading(id, false);
    }
  },

  // Internal — dispatch to reducer (for detail map)
  internal_dispatchBenchmarkDetail: (payload) => {
    const currentMap = get().benchmarkDetailMap;
    const nextMap = benchmarkDetailReducer(currentMap, payload);

    // Skip set when nothing changed — avoids unnecessary re-renders
    if (isEqual(nextMap, currentMap)) return;
    set({ benchmarkDetailMap: nextMap }, false, `dispatchBenchmarkDetail/${payload.type}`);
  },

  // Internal — update loading state for specific detail
  internal_updateBenchmarkDetailLoading: (id, loading) => {
    set(
      (state) => ({
        loadingBenchmarkDetailIds: loading
          ? [...state.loadingBenchmarkDetailIds, id]
          : state.loadingBenchmarkDetailIds.filter((i) => i !== id),
      }),
      false,
      'updateBenchmarkDetailLoading',
    );
  },
});

Store Guidelines

1. SWR keys as constants at top of file
2. useClientDataSWR for all data fetching (never useEffect)
3. onSuccess/onData callback updates store state
4. Refresh methods use mutate() to invalidate cache
5. Loading states in initialState, updated in onSuccess/onData
6. Mutations call service, then refresh relevant cache

Async Failure Boundary Contract

Every read hook returns an SWR response that includes error and mutate; the surface must consume them. A success-only init flag (!isInit, !map[id], data ?? []) is not enough: when the request fails, that flag often never flips, so the UI paints a permanent skeleton, a fake empty state, a false NotFound, or a confident zero-value metric.

Use the shared UI primitives:

• AsyncBoundary for normal loading / error / empty / data surfaces.
• AsyncError for custom layouts, detail pages, inline load-more failures, or metrics.

Core precedence for first-load failures:

const { data, error, isLoading, mutate } = useFetchXxx();

return (
  <AsyncBoundary
    data={data}
    empty={<EmptyState />}
    error={error}
    isEmpty={!error && data?.length === 0}
    isLoading={isLoading}
    onRetry={() => {
      void mutate();
    }}
  >
    <List items={data ?? []} />
  </AsyncBoundary>
);

Rules:

• Check error before empty / NotFound / zero defaults. Error is not a kind of empty.
• Keep already-loaded content on background revalidation failures; only replace the surface when there is no settled data to preserve.
• For detail maps, don't put the error branch after if (!map[id]) return <Skeleton/>. First-load failures never populate the map, making that error branch unreachable.
• For infinite scroll / load-more, persist a per-bucket loadMoreError and render an inline Retry row. Do not let an IntersectionObserver silently retry while the error is still unresolved.
• For merged fetched + static lists, branch on the fetched slice's error before merging. Static fallback rows can make a failed fetch look like a plausible partial catalog.

Layer 3: Component Usage

Fetching List Data

// ✅ CORRECT
const BenchmarkList = () => {
  // 1. Get the hook from store
  const useFetchBenchmarks = useEvalStore((s) => s.useFetchBenchmarks);

  // 2. Get list data
  const benchmarks = useEvalStore((s) => s.benchmarkList);
  const isInit = useEvalStore((s) => s.benchmarkListInit);

  // 3. Call the hook (SWR handles the data fetching)
  useFetchBenchmarks();

  // 4. Use the data
  if (!isInit) return <Loading />;
  return (
    <div>
      <h2>Total: {benchmarks.length}</h2>
      {benchmarks.map((b) => (
        <BenchmarkCard key={b.id} {...b} />
      ))}
    </div>
  );
};

Fetching Detail Data

// ✅ CORRECT
const BenchmarkDetail = () => {
  const { benchmarkId } = useParams<{ benchmarkId: string }>();

  const useFetchBenchmarkDetail = useEvalStore((s) => s.useFetchBenchmarkDetail);

  // Detail from map
  const benchmark = useEvalStore((s) =>
    benchmarkId ? s.benchmarkDetailMap[benchmarkId] : undefined,
  );

  // Per-item loading
  const isLoading = useEvalStore((s) =>
    benchmarkId ? s.loadingBenchmarkDetailIds.includes(benchmarkId) : false,
  );

  useFetchBenchmarkDetail(benchmarkId);

  if (!benchmark) return <Loading />;
  return (
    <div>
      <h1>{benchmark.name}</h1>
      <p>{benchmark.description}</p>
      {isLoading && <Spinner />}
    </div>
  );
};

Using Selectors (Recommended)

// src/store/eval/slices/benchmark/selectors.ts
export const benchmarkSelectors = {
  getBenchmarkDetail: (id: string) => (s: EvalStore) => s.benchmarkDetailMap[id],
  isLoadingBenchmarkDetail: (id: string) => (s: EvalStore) =>
    s.loadingBenchmarkDetailIds.includes(id),
};

// Component with selectors
const BenchmarkDetail = () => {
  const { benchmarkId } = useParams();
  const useFetchBenchmarkDetail = useEvalStore((s) => s.useFetchBenchmarkDetail);
  const benchmark = useEvalStore(benchmarkSelectors.getBenchmarkDetail(benchmarkId!));

  useFetchBenchmarkDetail(benchmarkId);

  return <div>{benchmark && <h1>{benchmark.name}</h1>}</div>;
};

Anti-pattern

// ❌ WRONG — Don't use useEffect for data fetching
const BenchmarkList = () => {
  const [data, setData] = useState([]);
  const [loading, setLoading] = useState(false);

  useEffect(() => {
    setLoading(true);
    lambdaClient.agentEval.listBenchmarks
      .query()
      .then(setData)
      .finally(() => setLoading(false));
  }, []);

  return <div>...</div>;
};

Mutations in Components

// Create — global mutation flag drives form loading
const CreateBenchmarkModal = () => {
  const createBenchmark = useEvalStore((s) => s.createBenchmark);
  const isCreating = useEvalStore((s) => s.isCreatingBenchmark);

  const handleSubmit = async (values) => {
    try {
      // Optimistic update + refresh happen inside createBenchmark
      await createBenchmark(values);
      message.success('Created successfully');
      onClose();
    } catch (error) {
      message.error('Failed to create');
    }
  };

  return (
    <Form onSubmit={handleSubmit} loading={isCreating}>
      ...
    </Form>
  );
};

// Update / delete — per-item loading so only the row being mutated spins
const BenchmarkItem = ({ id }: { id: string }) => {
  const updateBenchmark = useEvalStore((s) => s.updateBenchmark);
  const deleteBenchmark = useEvalStore((s) => s.deleteBenchmark);
  const isLoading = useEvalStore(benchmarkSelectors.isLoadingBenchmarkDetail(id));

  const handleUpdate = async (data) => {
    await updateBenchmark({ id, ...data });
  };

  const handleDelete = async () => {
    await deleteBenchmark(id);
  };

  return (
    <div>
      {isLoading && <Spinner />}
      <button onClick={handleUpdate}>Update</button>
      <button onClick={handleDelete}>Delete</button>
    </div>
  );
};

Why two patterns: create has no id yet, so a single isCreatingXxx flag is enough. Update/delete target a specific row, so global flags would freeze unrelated rows — keep per-item state in loadingXxxIds.

Need a fuller worked example?

The canonical Benchmark example above is the one to copy for a flat list + detail map. If you need to maintain a list keyed by a parent id (e.g. datasetMap[benchmarkId] because the same shape appears under multiple parents), read references/walkthrough.md — it walks through the full 6 steps (service → reducer → slice → store wiring → selectors → component) for that variant.

Common Patterns

Pattern 1: Pagination

Cache key array must include every parameter that should trigger a refetch.

useFetchTestCases: (params: { datasetId: string; limit: number; offset: number }) =>
  useClientDataSWR(
    params.datasetId ? [FETCH_TEST_CASES_KEY, params.datasetId, params.limit, params.offset] : null,
    () => agentEvalService.listTestCases(params),
    {
      onSuccess: (data) =>
        set({
          testCaseList: data.data,
          testCaseTotal: data.total,
          isLoadingTestCases: false,
        }),
    },
  );

Pattern 2: Dependent Fetching

Both hooks run in parallel — SWR dedupes, no manual sequencing needed.

const BenchmarkDetail = () => {
  const { benchmarkId } = useParams();
  const useFetchBenchmarkDetail = useEvalStore((s) => s.useFetchBenchmarkDetail);
  const useFetchDatasets = useEvalStore((s) => s.useFetchDatasets);

  useFetchBenchmarkDetail(benchmarkId);
  useFetchDatasets(benchmarkId);

  return <div>...</div>;
};

Pattern 3: Conditional Fetching

Pass undefined to disable the hook entirely.

// only fetch when modal is open AND id present
useFetchDatasetDetail(open && datasetId ? datasetId : undefined);

Pattern 4: Cross-domain Refresh

deleteBenchmark: async (id) => {
  await agentEvalService.deleteBenchmark(id);
  await get().refreshBenchmarks();
  await get().refreshDatasets(id); // related cache invalidated too
};

Migration Guide: useEffect → Store SWR

Before (❌ Wrong)

const TestCaseList = ({ datasetId }: Props) => {
  const [data, setData] = useState<any[]>([]);
  const [loading, setLoading] = useState(false);

  useEffect(() => {
    setLoading(true);
    lambdaClient.agentEval.listTestCases
      .query({ datasetId })
      .then((r) => setData(r.data))
      .finally(() => setLoading(false));
  }, [datasetId]);

  return <Table data={data} loading={loading} />;
};

After (✅ Correct)

// 1. Add service method
class AgentEvalService {
  async listTestCases(params: { datasetId: string }) {
    return lambdaClient.agentEval.listTestCases.query(params);
  }
}

// 2. Add store slice hook
export const createTestCaseSlice: StateCreator<...> = (set) => ({
  useFetchTestCases: (params) =>
    useClientDataSWR(
      params.datasetId ? [FETCH_TEST_CASES_KEY, params.datasetId] : null,
      () => agentEvalService.listTestCases(params),
      {
        onSuccess: (data) =>
          set({ testCaseList: data.data, isLoadingTestCases: false }),
      },
    ),
});

// 3. Component reads from store
const TestCaseList = ({ datasetId }: Props) => {
  const useFetchTestCases = useEvalStore((s) => s.useFetchTestCases);
  const data = useEvalStore((s) => s.testCaseList);
  const loading = useEvalStore((s) => s.isLoadingTestCases);

  useFetchTestCases({ datasetId });

  return <Table data={data} loading={loading} />;
};

Troubleshooting

Summary Checklist

When adding new data fetching:

Step 1: Types & State

See store-data-structures for details.

• Define types in @lobechat/types: Detail type + List item type
• State structure: xxxList: XxxListItem[], xxxDetailMap: Record<string, Xxx>, loadingXxxDetailIds: string[]
• Reducer if optimistic updates are needed

Step 2: Service Layer

• Create service in src/services/xxxService.ts
• Methods: listXxx(), getXxx(id), createXxx(), updateXxx(), deleteXxx()

Step 3: Store Actions

• initialState.ts with state structure
• action.ts with:
  • useFetchXxxList(), useFetchXxxDetail(id) — SWR hooks
  • refreshXxxList(), refreshXxxDetail(id) — cache invalidation
  • CRUD methods calling service
  • internal_dispatch, internal_updateLoading if using reducer
• selectors.ts (optional but recommended)
• Integrate slice into main store + initialState

Step 4: Component Usage

• Use store hooks (NOT useEffect)
• Destructure and consume error / mutate; wrap first-load surfaces in AsyncBoundary or render AsyncError before empty / NotFound / zero defaults
• List pages: access xxxList array
• Detail pages: access xxxDetailMap[id]
• Use loading states for UI feedback
• Infinite-scroll failures persist as a visible tail Retry row, not a silent catch

Mental model: Types → Service → Reducer → Slice → Component 🎯

Related Skills

• store-data-structures — How to structure List and Detail data in stores
• zustand — General Zustand patterns and best practices