Harper Resources

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:

Extending a table

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

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

Wrapping an external source

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:

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):

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:

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
• Applications