---
name: harper-resources
description: "writing or editing Harper…"
---

# Harper Resources

## Overview

A **Resource** is a class that provides a unified interface for a set of records or
entities. Resources are how you add custom server-side behavior to a Harper app.
They are loaded by the `jsResource` extension (default file `resources.js`) and,
when **exported**, become live REST and GraphQL endpoints.

A resource either **extends a database table** (to customize an existing table's
behavior) or **extends the base `Resource` class** (to expose data from anywhere —
an external API, a computed view, an in-memory source).

## Method → HTTP verb mapping

The Resource API mirrors REST. Override the method matching the operation you want
to customize:

| Method | HTTP | Use |
| --- | --- | --- |
| `get(target)` | GET | Retrieve a record/collection |
| `post(data)` | POST | Create |
| `put(target, data)` | PUT | Replace |
| `patch(target, data)` | PATCH | Partial update |
| `delete(target)` | DELETE | Remove |
| `search(query)` | GET (query) | Query with conditions |
| `subscribe` / `publish` | MQTT/WebSocket | Real-time |

## Extending a table

Add computed fields or guard logic while keeping the table's built-in behavior via
`super`:

```javascript
export class MyTable extends tables.MyTable {
  static async get(target) {
    const record = await super.get(target);
    return { ...record, computedField: 'value' };
  }
}
```

## Wrapping an external source

```javascript
export class MyExternalData extends Resource {
  static async get(target) {
    const response = await fetch(`https://api.example.com/${target.id}`);
    return response.json();
  }
}
```

## Making a resource an endpoint

A resource becomes an endpoint when it is **exported** and `rest: true` (and/or
`graphqlSchema`) is enabled in `config.yaml`:

```yaml
rest: true
graphqlSchema:
  files: schema.graphql
jsResource:
  files: resources.js
```

Resources can also be registered programmatically with `server.resources.set()`.
See [[harper-config-yaml]] for the extension wiring, [[harper-schema-graphql]] for
how the schema defines the tables resources extend, and [[harper-realtime]] when
`subscribe`, `publish`, or WebSocket behavior is part of the feature.

## Throwing HTTP status errors

Harper's thrown-error response writer reads **`error.statusCode`** (falling back
to `500`). A plain `error.status` is **ignored** — throw an error with only
`status` set and every intended `4xx` is served as a `500`. Verified on
harperdb 4.7.32.

Always set `statusCode` (keep `status` too only if callers or tests read it):

```javascript
static async post(target, data, context) {
  if (!context.user) {
    const error = new Error('Authentication required');
    error.statusCode = 401; // NOT `error.status` — Harper reads statusCode
    throw error;
  }
  // ...
}
```

A shared helper keeps every throw site correct:

```javascript
function throwStatus(message, status) {
  // Set both: `statusCode` is what Harper serves; `status` is kept for
  // returned-response symmetry and any caller/test that reads it.
  throw Object.assign(new Error(message), { status, statusCode: status });
}
```

The `harper-require-statuscode-on-thrown-error` ast-grep rule flags errors that
carry `status` without `statusCode`. Pass `context` through to `super` and nested
table calls so authorization and the request transaction stay aligned — see
[[harper-rest-queries]] for context propagation and iterator draining.

## Project conventions (TS is source)

- **Write resources in TypeScript under `src/`. `harper-app/resources.js` is a
  generated artifact** produced by `bun run build`. Never edit `resources.js` by
  hand — change the TypeScript and rebuild. See [[harper-build-and-deploy]].
- Operational scripts that touch resources (seed, smoke, verify, ingest, crawl,
  extraction) must run from compiled JavaScript or generated Harper assets, not
  stale checked-in JS.
- Prefer immutable data flow: `readonly` types, pure transformations, copies, and
  explicit returns. Do not mutate parameters, records, arrays, or config objects
  unless an API forces it, and document the exception locally.
- Avoid `any`, broad casts, and `ts-ignore`. If an external API forces an escape
  hatch, isolate it behind a typed adapter.

## Build the real thing

If an endpoint needs a schema change, a seed path, or a deploy script change, make
that change — do not ship a client-side workaround or silently downgrade to a stub
or mock. A change is unfinished until the local build and the relevant deployed or
smoke path agree.

## Verification

Run `bun run build`, `bun run typecheck`, and the smallest relevant test. For an
endpoint change, also hit the actual REST/GraphQL route against a local or deployed
Harper instance (the project smoke command) and confirm the response shape.

## Sources

- [Resources overview](https://docs.harperdb.io/reference/v5/resources/overview)
- [Applications](https://docs.harperdb.io/docs/developers/applications)
