cratis-arc-query-typescript

Add a query to an Arc read model in TypeScript (Node.js server)

In Arc for TypeScript a read model is a decorated class, and its reads are static methods on it marked @query(). Each query becomes a route; Arc binds the arguments, resolves services, pages and sorts, and wraps every answer in the same QueryResult envelope. There is no controller to write.

Arc for TypeScript is a source preview: @cratis/arc.core and the other server packages are not published to npm, and the API may change. @cratis/arc is the separate, published client that generated query proxies import in a frontend. Project setup, the builder, and hosts are in cratis-arc-command-typescript.

Verified product sources

Read references/product-sources.md for the source files; RxJS is an optional peer for RxJS sources.

Declare a read model and its queries

Samples/Tasks/Features/Tasks/Listing/Listing.ts:

import { field } from '@cratis/fundamentals';
import { query, readModel, service } from '@cratis/arc.core';
import type { BehaviorSubject } from 'rxjs';
import { TaskId } from '../TaskId.js';
import { TaskTitle } from '../TaskTitle.js';
import { Tasks } from '../Tasks.js';

@readModel()
export class TaskItem {
    @field(TaskId) id!: TaskId;
    @field(TaskTitle) title!: TaskTitle;

    @query(service(Tasks))
    static allTasks(tasks: Tasks): TaskItem[] { return tasks.all(); }

    @query()
    static taskById(id: TaskId, tasks: Tasks): TaskItem | undefined { return tasks.byId(id); }

    @query()
    static observeAllTasks(tasks: Tasks): BehaviorSubject<TaskItem[]> { return tasks.observeAll(); }
}

Arc serves a method only when all three hold:

• the class carries @readModel() (from @cratis/arc.core) and is exported under the discovery root,
• the method is static,
• the method carries @query(...).

Any other static method is an ordinary helper with no route. @query() on an instance or private method throws when the class loads; @roles, @authorize, @allowAnonymous or @path on a static method without @query() fails at build(). The @field declarations (from @cratis/fundamentals) describe the shape Arc encodes on the way out and that the proxy generator uses for the frontend model — keep one on every wire property.