setup-data-layer

name	setup-data-layer
description	Wire a new entity into the data layer — model, store binding, DataSet with authorization/hooks, optional entity sync. Use when the user asks to add an entity, persist a model, expose a collection, or set up a new DataSet.

setup-data-layer

Add an entity end-to-end through the FuryStack data stack: model → physical store → throw-by-default token wiring → DataSet with auth/hooks → entity sync. Read .cursor/rules/REST_SERVICE.mdc, .cursor/rules/CODE_STYLE.mdc, and .cursor/rules/TYPESCRIPT_GUIDELINES.mdc before authoring; this skill owns the workflow.

StackCraft layout note: Stores split by module — define stores and DataSets in service/src/app-models/<module>/setup-<module>-store.ts. Entity sync registration lives in service/src/setup-entity-sync.ts. The skill's generic service/src/setup-store.ts reference should be translated to the per-module path.

Step 1 — Define the model

Create the entity class in common/src/models/<entity>.ts. Use declare for fields so TS doesn't emit them as initialized properties (compatibility with FileSystem / DB stores):

export class User {
  declare username: string
  declare displayName: string
  declare roles: string[]
}

Re-export from common/src/models/index.ts and common/src/index.ts.

Step 2 — Pick a backend

Backend	Use case	Helper
InMemoryStore	Tests, ephemeral data, sessions	defineStore + new InMemoryStore({...})
defineFileSystemStore	Local persistence (small datasets, dev)	one-liner
defineMongoDbStore	Document data, larger scale	one-liner with client, db, collection
defineSequelizeStore	Relational	one-liner with sequelizeModel, initModel?
defineRedisStore	Cache-shaped persistence	one-liner with client

If the backend needs to be authored from scratch, run the implement-store-adapter skill first (or read LIBRARY_DEVELOPMENT.mdc Stores section).

Step 3 — Define the physical store

Add to service/src/setup-store.ts (or a per-module setup file):

import { defineFileSystemStore } from '@furystack/filesystem-store'
import { join } from 'path'
import { User } from 'common'

const UsersFileStore = defineFileSystemStore({
  name: 'app/UsersFileStore',
  model: User,
  primaryKey: 'username',
  fileName: join(process.cwd(), 'users.json'),
  tickMs: 30_000,
})

If TypeScript widens TPrimaryKey to keyof T, pass explicit generics: defineFileSystemStore<User, 'username'>({ ... }).

Step 4 — Bind to framework throw-by-default tokens (if applicable)

Some FuryStack-shipped tokens (UserStore, SessionStore, PasswordCredentialStore, etc.) default to factories that throw NotConfiguredError. Bind your concrete store:

import { UserStore } from '@furystack/rest-service'

export const setupStore = (injector: Injector): void => {
  injector.bind(UserStore, ({ inject }) => inject(UsersFileStore))
  // ...
}

For app-defined entities with no framework token, skip this step — the defineXxxStore token is already singleton-cached.

Step 5 — Define the DataSet

DataSets are the write gateway. Add to service/src/setup-store.ts or a per-module file:

import { defineDataSet, type DataSetToken } from '@furystack/repository'
import { authorizedDataSet } from './authorization/authorized-only.js'

export const UserDataSet: DataSetToken<User, 'username'> = defineDataSet({
  name: 'app/UserDataSet',
  store: UserStore, // can be a framework token or a local store token
  settings: {
    ...authorizedDataSet, // role checks
    onEntityAdded: ({ injector, entity }) => {
      /* side effects */
    },
    authorizeUpdate: async ({ entity, injector }) => ({
      isAllowed: entity.username !== 'system',
      message: 'Cannot update the system user',
    }),
  },
})

• authorizeAdd / authorizeGet / authorizeRemove / authorizeUpdate for role-based gates
• onEntityAdded / onEntityUpdated / onEntityRemoved for side effects (audit log, notifications)
• Annotate the type explicitly (DataSetToken<T, PK>) — inline callbacks can widen TPrimaryKey to keyof T

Step 6 — Application code consumes the DataSet token

Application code resolves the DataSet token, never the store token directly:

import { getDataSetFor } from '@furystack/repository'

const userDataSet = getDataSetFor(injector, UserDataSet)
await userDataSet.add(injector, { username: 'alice', displayName: 'Alice', roles: [] })

The furystack/no-direct-store-token lint rule enforces this. Direct store access is allowed only inside DataSet factories, store implementations testing themselves, and test data seeding.

For server-internal operations (system user, scheduled jobs) wrap in useSystemIdentityContext:

import { useSystemIdentityContext } from '@furystack/core'
import { usingAsync } from '@furystack/utils'

await usingAsync(useSystemIdentityContext({ injector, username: 'Seeder' }), async (sys) => {
  const ds = getDataSetFor(sys, UserDataSet)
  await ds.add(sys, seedUser)
})

Step 7 — Entity sync (optional)

If frontend caches need to invalidate when the entity changes, opt-in via useEntitySync:

import { useEntitySync } from '@furystack/rest-service'

useEntitySync(injector, { models: [UserDataSet, OrderDataSet] })

This emits change events the frontend can subscribe to. Each model passed in must be a DataSetToken, not a raw store token.

Step 8 — REST endpoints (if exposed)

If users need to read/write this entity over HTTP, run the create-api-endpoint skill — pick the DataSet-backed CRUD branch and use createGetCollectionEndpoint(UserDataSet) etc.

Step 9 — Seed (optional)

For initial data, add to service/src/seed.ts (or service/src/bin/seed-<entity>.ts):

await usingAsync(useSystemIdentityContext({ injector, username: 'Seeder' }), async (sys) => {
  const ds = getDataSetFor(sys, UserDataSet)
  if ((await ds.count(sys, {})) === 0) {
    await ds.add(sys, { username: 'admin', displayName: 'Admin', roles: ['admin'] })
  }
})

Run with yarn seed.

Step 10 — Tests

Run write-tests skill. Cover:

• DataSet auth — add / update / remove blocked when authorize callback returns isAllowed: false
• Hooks — onEntityAdded etc. fire with correct payloads
• Type integrity — primary key generic doesn't widen
• Disposal — injector[Symbol.asyncDispose]() cleans up the store

Wrap every Injector and store usage in usingAsync per TESTING_GUIDELINES.mdc.

Step 11 — Verify

yarn lint
yarn build
yarn test

If furystack/no-direct-store-token fires, the test or app code resolved the wrong token.

Output

Report:

• Model file + exports
• Physical store factory
• DataSet token + auth/hooks
• Framework token bindings, if any
• Entity sync registration, if any
• Endpoints generated, if any (link to create-api-endpoint invocation)
• Seeded counts, if any