Decaf's Nano (CouchDB) Module

A lightweight adapter layer and utilities to use CouchDB via the Nano client within the decaf-ts ecosystem. It provides a NanoAdapter with repository-friendly CRUD, bulk operations, indexing, user/database management helpers, and a change feed dispatcher, plus typed flags and configuration for ergonomic, testable data access.

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Description

This package integrates CouchDB via the Nano client into the decaf-ts data stack. It exposes a focused set of primitives that make CouchDB usage consistent with other decaf-ts backends (TypeORM, HTTP, Pouch, etc.), while retaining Nano’s flexibility.

Core elements and their intents:

NanoAdapter
- Bridges decaf-ts Repository operations with Nano’s DocumentScope API.
- Implements repository-friendly CRUD: create, read, update, delete, plus bulk variants (createAll, readAll, updateAll, deleteAll).
- Preserves and manages CouchDB revision metadata transparently via PersistenceKeys.METADATA and CouchDBKeys.REV.
- Provides raw Mango query capability (raw) and index management (index).
- Offers connection and administration helpers: connect, createDatabase, deleteDatabase, createUser, deleteUser.
- Exposes Dispatch() to construct a NanoDispatch for change feed observation.
- Normalizes operation flags via flags(), ensuring user context is propagated from NanoFlags to the underlying operations.
NanoDispatch
- A Dispatch implementation that subscribes to CouchDB’s continuous changes feed through Nano.
- Parses change feed frames, groups them by table and operation (CREATE/UPDATE/DELETE), and notifies observers through updateObservers.
- Handles reconnection attempts and keeps track of the last processed update step (observerLastUpdate) for resilience.
NanoRepository
- A typed alias that binds Repository to the Nano-specific types: MangoQuery, NanoAdapter, NanoFlags, and Context.
- Enables consumers to use a familiar Repository API with CouchDB when paired with NanoAdapter.
Types and constants
- NanoFlags extends RepositoryFlags with a required user object (name, roles?) for consistent auth context propagation.
- NanoConfig captures the minimal connection shape (user, password, host, dbName) for setting up adapters.
- NanoFlavour identifies this backend for selection in multi-backend setups.
- VERSION exposes the package version string.

Design considerations:

Predictable metadata management: CouchDB’s _rev is captured in internal metadata, avoiding accidental leakage into domain models.
Bulk operations are error-aware: mixed success/failure responses are aggregated and surfaced as InternalError, preserving the failing reasons from Nano.
Testability: All core behaviors (CRUD, bulk, raw, admin helpers, dispatch) are covered by unit tests and written to be easily mocked.
Interop-first: Reuses shared types from @decaf-ts/for-couchdb (e.g., MangoQuery, CouchDBKeys) so that query building and index generation are consistent across CouchDB-based adapters.

How to Use

This guide shows practical, non-duplicated examples for all public APIs in @decaf-ts/for-nano using the repository pattern. The adapter class is not meant to be accessed directly; instead, always obtain a repository with Repository.forModel(Model).

Prerequisites:

CouchDB server reachable from your app.
Install the package: npm i @decaf-ts/for-nano @decaf-ts/for-couchdb @decaf-ts/core @decaf-ts/db-decorators @decaf-ts/decorator-validation nano
Importing from @decaf-ts/for-nano registers the Nano backend with the core Repository system.

Define a model and get a repository

Description: Declare a model with table/primary-key decorators and get a Nano-powered repository for it. The flavour is auto-wired by importing @decaf-ts/for-nano.

import {
  BaseModel,
  Repository,
  pk,
  uses,
} from "@decaf-ts/core";
import { model, Model, ModelArg, required } from "@decaf-ts/decorator-validation";
import type { NanoRepository } from "@decaf-ts/for-nano";

@uses("nano")
@model()
class UserModel extends BaseModel implements Model {
  @pk({ type: "String" })
  id!: string; // primary key

  @required()
  name!: string;

  constructor(arg?: ModelArg<UserModel>) {
    super(arg);
  }
}

const repo: NanoRepository<UserModel> = Repository.forModel<UserModel, NanoRepository<UserModel>>(UserModel);

Flags with user context

Description: Pass NanoFlags in repository calls; the user info is propagated to operations by the adapter under the hood.

import type { NanoFlags } from "@decaf-ts/for-nano";

const flags: NanoFlags = {
  user: { name: "tester", roles: ["writer"] },
};

CRUD: create and read a single document

Description: Insert a document and read it back. CouchDB revisions are stored in PersistenceKeys.METADATA transparently.

import { PersistenceKeys } from "@decaf-ts/core";

const created = await repo.create(new UserModel({ id: "user:1", name: "Ada" }));
// created[PersistenceKeys.METADATA] contains the new revision string, e.g., "1-a"

const loaded = await repo.read("user:1");
console.log(loaded.name);

Bulk create and bulk read

Description: Insert multiple documents and then fetch them by IDs. Bulk operations aggregate errors.

const users = [
  new UserModel({ id: "user:2", name: "Lin" }),
  new UserModel({ id: "user:3", name: "Grace" }),
];
const createdMany = await repo.createAll(users);

const fetchedMany = await repo.readAll(["user:2", "user:3"]);

Update and updateAll

Description: Update requires the previous revision in metadata. The new revision is written back into metadata.

let u = await repo.read("user:1");
// ... mutate
u.name = "Ada Lovelace";
// u already has PersistenceKeys.METADATA from read()
u = await repo.update(u);

// Bulk update requires each model to carry its matching metadata
const u2 = await repo.read("user:2");
const u3 = await repo.read("user:3");
const updatedMany = await repo.updateAll([u2, u3]);

Delete and deleteAll

Description: Delete a single document, or delete in bulk by IDs.

const deleted = await repo.delete("user:3");

const deletedMany = await repo.deleteAll(["user:1", "user:2"]);

Query with selectors (instead of raw Mango)

Description: Use the Repository query API to filter and project results.

import { Condition, OrderDirection } from "@decaf-ts/core";

// Select all as full UserModel objects
const all = await repo.select().execute();

// Select only specific attributes
const projected = await repo.select(["name"]).execute();

// Conditional queries
const nameEq = Condition.attribute<UserModel>("name").eq("Ada Lovelace");
const named = await repo.select().where(nameEq).execute();

// Ordering (requires proper indexes configured for CouchDB)
const ordered = await repo.select().orderBy(["name", OrderDirection.ASC]).execute();

Observe changes via repository

Description: Subscribe to CREATE/UPDATE/DELETE events using the Observer interface. The repository wires Nano’s change feed internally.

import type { Observer } from "@decaf-ts/core";
import { OperationKeys } from "@decaf-ts/db-decorators";

const observer: Observer = {
  async refresh(table: string, operation: OperationKeys | string, ids: string[]) {
    if (operation.toString() === OperationKeys.DELETE.toString()) {
      console.log(`Deleted from ${table}:`, ids);
    }
  },
};

await repo.observe(observer);
// ... later
await repo.unObserve(observer);

Choose the backend via NanoFlavour

Description: Use NanoFlavour as an identifier in multi-backend setups.

import { NanoFlavour } from "@decaf-ts/for-nano";
console.log(NanoFlavour); // "nano"

Use NanoRepository typing

Description: Bind your model type to a repository powered by the Nano backend.

import type { NanoRepository } from "@decaf-ts/for-nano";
import type { Model } from "@decaf-ts/decorator-validation";

class MyModel implements Model {
  _id!: string;
}

let myRepo!: NanoRepository<MyModel>;

Access package VERSION

Description: Read the module’s version string if you need it for diagnostics.

import { VERSION } from "@decaf-ts/for-nano";
console.log("for-nano version:", VERSION);

Advanced (optional): Administration helpers

Description: If you must manage CouchDB resources, @decaf-ts/for-nano exports static helpers on NanoAdapter (no direct instantiation required). These are not part of the Repository API.

import { NanoAdapter } from "@decaf-ts/for-nano";

// Build a Nano (CouchDB) connection
const url = NanoAdapter.connect("admin", "secret", "localhost:5984", "http");

// Ensure a database exists / manage users
await NanoAdapter.createDatabase(url, "mydb");
// ... createUser/deleteUser, deleteDatabase, etc.