Type Inference Mental Model

DX rules of thumb:

Token in → narrowed type out
- Pass a literal entity token ('user' as const) to get token-narrowed record types at call sites (no generics).
Domain vs storage
- Reads return storage records (keys included). Use entityManager.removeKeys(entityToken, records) in handlers when you want domain shapes.
Projection K channel
- When you pass projection tuples (const), item shapes narrow at the call site. The QueryBuilder preserves this through the adapter.
Values-first config can narrow index/page-key types
- If your EntityClient carries a config literal type (CF), createQueryBuilder infers index tokens (ITS) and per-index page keys automatically.
- How you capture CF depends on your setup (for example, a values-first EntityManager factory), or by explicitly typing the client as EntityClient<C, typeof cf>.
- Without CF, ITS falls back to string.

Patterns

// Token-aware get with projection tuple (const narrows the shape)
const out = await client.getItem('user', { hashKey2: 'h', rangeKey: 'r' }, [
  'a',
] as const);

// QueryBuilder narrows per-index page keys automatically when the client carries CF
const qb = createQueryBuilder({
  entityClient: client,
  entityToken: 'user',
  hashKeyToken: 'hashKey2',
});

Type Inference Mental Model

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