Handling the API request with an API Controller

Inside of the users/useCases/createUser folder, we find the CreateUserController.

The CreateUserController has a single dependency injected into it. The CreateUserUseCase. It's the Application Service/Use Case that does all the action.

The responsibilities of a controller are to:

  • Invoke the CreateUserUseCase.
  • Respond to the API call with the appropriate HTTP response code based on the result of the executed use case.

See the CreateUserController below.

// CreateUsersController - Handling the request data from 
// the internet and passing it to the dependency injected 
// use case class for execution.

// users/useCases/createUser/CreateUserController.ts

import { CreateUserUseCase } from "./CreateUserUseCase"
import { CreateUserDTO } from "./CreateUserDTO"
import { CreateUserErrors } from "./CreateUserErrors"
import { BaseController } from "../../../../shared/infra/http/models/BaseController"
import { TextUtils } from "../../../../shared/utils/TextUtils"
import { DecodedExpressRequest } from "../../infra/http/models/decodedRequest"
import * as express from "express"

export class CreateUserController extends BaseController {
  private useCase: CreateUserUseCase

  constructor(useCase: CreateUserUseCase) {
    this.useCase = useCase

  async executeImpl(
    req: DecodedExpressRequest,
    res: express.Response
  ): Promise<any> {
    let dto: CreateUserDTO = req.body as CreateUserDTO

    dto = {
      username: TextUtils.sanitize(dto.username),
      email: TextUtils.sanitize(dto.email),
      password: dto.password,

    try {
       * Execute the CreateUserUseCase use case.

      const result = await this.useCase.execute(dto)

      if (result.isLeft()) {
        const error = result.value

         * This is an example of how one can standardize a
         * RESTful API's error messages.
         * We utilize the Use Case Error types.

        switch (error.constructor) {
          case CreateUserErrors.UsernameTakenError:
            return this.conflict(error.errorValue().message)
          case CreateUserErrors.EmailAlreadyExistsError:
            return this.conflict(error.errorValue().message)
            return this.fail(res, error.errorValue().message)
      } else {
        return this.ok(res)
    } catch (err) {
      return this.fail(res, err)

Like this?: If you like the way this Express.js controller uses declarative response methods, check out "Clean & Consistent Express.js Controllers | Enterprise Node.js + TypeScript".

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