---
title: Change a sample
editUrl: https://github.com/Cratis/Arc.TypeScript/edit/main/Documentation/contributing/samples.md
description: Regenerate proxies and metadata, lint, and check client generation after you change the Tasks or Library sample, and find where each Arc for .NET test-app behavior is covered in this repository.
---


The Tasks and Library samples in this repository are checked by the same gate as the packages. Both samples commit generated metadata and co-located proxies, so a change to a decorated artifact has to be followed by a regeneration, or `yarn ci` fails. This page is for contributors to this repository; applications have their own scripts.

## After you change a slice

Run these from the repository root. The `generate-proxies` scripts run the proxy generator from its `dist` folder, so run `yarn build` first.

| Command | What it does |
| --- | --- |
| `yarn workspace @cratis/arc.core.sample.tasks generate-proxies` | Regenerates `Samples/Tasks/Features/generatedMetadata.ts`, writes proxies beside its backend slices, and type-checks the proxies |
| `yarn workspace @cratis/arc.sample.library generate-proxies` | Regenerates `Samples/Library/Features/generatedMetadata.ts` and proxies beside its backend slices |
| `yarn check:metadata` | Fails when either sample's committed metadata differs from its source |
| `yarn check:proxies` | Fails when either sample's committed proxies differ from regenerated output, or new proxies are untracked; run after both `generate-proxies` commands |
| `yarn lint:tasks:arc` | Runs the Arc ESLint rules over `Samples/Tasks/Features` with type information |
| `yarn test:client-generation` | Builds, regenerates the Tasks proxies, compiles the client fixtures, and runs the generated proxies against Express, Fastify, and Hono |

Commit the regenerated files with the source change. Do not hand-edit generated metadata or browser proxies.

## Where the .NET test-app behaviors live

Arc for .NET exercises its hosts with two test applications in the Arc repository: `TestApps/ArcCore`, a standalone Arc.Core host, and `TestApps/AspNetCore`, an ASP.NET Core host with MongoDB and Swagger. Both share their features from `TestApps/Shared`. This repository has no test-app folders of the same name. Each behavior is covered by a sample, an adapter suite, or a contract check instead:

| Behavior | .NET reference (Arc 22.45.0) | Arc for TypeScript | Checked by |
| --- | --- | --- | --- |
| Standalone host without a web framework | `TestApps/ArcCore/Program.cs` | `Samples/Tasks/main.ts` with `app.run()` | `yarn build`, `yarn check:metadata` |
| Route prefix, skipped namespace segments, and command name in route | `ArcCore/Program.cs` options | `generatedApis` options | `Source/Core/for_ArcApplicationBuilder/when_building_model_bound_routes` |
| Model-bound command and read model | `Shared/ModelBoundCommand.cs`, `ModelBoundReadModel.cs` | `Samples/Tasks` `RegisterTask` and `TaskItem`; `Samples/Library` slices | Slice specs under each sample's `for_*` folders |
| Command validator | `AspNetCore/DoStuffValidator.cs` | `TaskTitleValidator` in Tasks; `AddBookValidator` in Library | `when_validating/with_an_empty_title`, `when_adding/with_an_empty_title` |
| Query by argument, paging, and sorting | `Shared/Features/QueryShowcase` | Tasks `taskById` and `allTasks`; Library `authorsPage` | `when_performing/with_a_concept_argument`, `with_sorting_and_paging`, Library `when_paging` |
| Observable queries | `Shared/Features/Ticker`, `LiveFeed`, `ObservableCollection`, `ChangeStream` | Tasks `observeAllTasks` (RxJS `BehaviorSubject`); Library `allAuthors` from Chronicle | Tasks `when_collecting/with_current_value`; `ContractTests/Client/observable-*.test.mjs` over SSE, WebSockets, and the hub |
| Authentication handlers | `Shared/Authentication` cookie and Microsoft identity platform handlers | `jwtBearer()` and `microsoftIdentityPlatform()`; a native principal in the Library host | `Source/Core/authentication/for_*`; `Source/Express/for_identityHosts` |
| Anonymous and authenticated queries, roles, and cross-cutting authorization filters | `Shared/Features/AuthenticationQueries`, `CrossCuttingAuthorization` | `@roles('Librarian')` in Library; authorization filters in Arc.Core | Library `with_librarian_role`, `without_librarian_role`; `yarn test:conformance` |
| Host adapters | `AspNetCore/Program.cs` (ASP.NET Core) | `@cratis/arc.express`, `@cratis/arc.fastify`, `@cratis/arc.hono`; Library runs on Express | `Source/{Express,Fastify,Hono}/for_cratisArc`; `yarn test:client-generation` runs generated proxies against all three |
| MongoDB collections and the change-stream watcher | `AspNetCore/Features/MongoWatcher` | `@cratis/arc.mongodb` `observe()` and `MongoDBWatcher` | `Source/MongoDB/run-integration.sh`, including `with_each_http_adapter` |
| React frontend with generated proxies | `ArcCore/main.tsx`, `AspNetCore/main.tsx`, `Shared/Features/*Page.tsx` | `Samples/Library/Features/**/*.tsx` (app shell in `Web/src`) | `yarn workspace @cratis/arc.sample.library test:e2e` exercises the proxies, not the browser UI |
| API description | Swagger UI through `Cratis.Arc.Swagger` | `GET /openapi.json`, without a bundled UI | `Source/Core/openApi/for_renderOpenApi` |

Three .NET behaviors have no counterpart by design:

- **Controllers.** `AspNetCore/Commands.cs`, `ObservableQueries.cs`, and `LiveFeedController.cs` use ASP.NET controllers. Arc for TypeScript serves only model-bound and low-level operations; routes you add to your host sit beside Arc.
- **Cookie authentication.** The shared `CookieAuthenticationHandler` is a .NET test fixture. Use your host's session handling and a [native principal](/arc/backend/typescript/hosts/native-principal/).
- **`FromRequest` binding.** It is C#-only; see [OpenAPI](/arc/backend/typescript/open-api/#topics).

Add a runnable sample only for a journey no sample, adapter suite, or contract check demonstrates yet, not to match a .NET folder name.

## Before you open a pull request

`yarn ci` runs all of the above with the rest of the gate. [Contributing](https://github.com/Cratis/Arc.TypeScript/blob/main/CONTRIBUTING.md) lists every step, and [Prepare and publish a TypeScript release](/arc/backend/typescript/contributing/releases/) covers release checks and publication.

## Related

- [Keep a behavior together in a vertical slice](/arc/backend/typescript/vertical-slices/)
- [Proxy generation](/arc/backend/typescript/proxy-generation/)