UseCase Pattern

What It Is

A UseCase is a single-method orchestrator that encapsulates one business operation (e.g., CreateTenantUseCase, PublishEntryUseCase). Each UseCase is a DI abstraction with an execute method that returns Result<T, E>.

Interface Shape

interface SomeUseCase.Interface {
    execute(input: Input): Promise<Result<ReturnType, ErrorType>>;
}

• Input, a typed object specific to the use case
• Result, always returns Result<T, E> from webiny/api
• Error, extends BaseError with a unique code

How to Use a UseCase

UseCases are injected as dependencies into EventHandlers, other UseCases, or GraphQL resolvers via DI.

import { SomeUseCase } from "webiny/api/<category>";
import { SomeEventHandler } from "webiny/api/<category>";

class MyHandler implements SomeEventHandler.Interface {
  constructor(private someUseCase: SomeUseCase.Interface) {}

  async handle(event: SomeEventHandler.Event) {
    const result = await this.someUseCase.execute({/* input */});

    if (result.isFail()) {
      console.error(result.error.message);
      return;
    }

    const value = result.value;
    // ... use value
  }
}

export default SomeEventHandler.createImplementation({
  implementation: MyHandler,
  dependencies: [SomeUseCase]
});

How to Override a UseCase

To replace the default implementation, register your own:

import { SomeUseCase } from "webiny/api/<category>";

class CustomImplementation implements SomeUseCase.Interface {
  async execute(input) {
    // Custom logic
    return Result.ok(/* ... */);
  }
}

export default SomeUseCase.createImplementation({
  implementation: CustomImplementation,
  dependencies: []
});

Registration

YOU MUST include the full file path with the .ts extension in the src prop. For example, use src={"@/extensions/my-extension.ts"}, NOT src={"@/extensions/my-extension"}. Omitting the file extension will cause a build failure.