Node.js typescript中的作用域

我在nodeJs中创建了一个示例应用程序，它使用pgpromise在Postgres中执行查询。并用一个名为PostgresDataAccess的类包装它。在下面的代码中，为什么我不能从get和getOne函数访问“dal”对象。“this”关键字返回undefined。有人能解释一下吗

import { Router, Request, Response, NextFunction } from 'express';
import { PostgresDataAccess } from '../dal/postgres';

const config = require('../../config/config');

export class ProjectRouter {
  public router: Router;

  dal: PostgresDataAccess;

  /**
   * Construct the Project Router.
   */
  constructor() {
    this.dal = new PostgresDataAccess(config);
    this.router = Router();
    this.init();
  }

  /**
   * Take each handler, and attach to one of the Express.Router's endpoints.
   */
  init() {
    this.router.get('/', this.get);
    this.router.get('/:id', this.getOne);
  }

  /**
   * GET: Returns all projects.
   */
  get(req: Request, res: Response, next: NextFunction) {
    let projects = this.dal.queryDb('select * from projects', null, res);
  }

  /**
   * GET: Retuns one project by id.
   */
  getOne(req: Request, res: Response, next: NextFunction) {
    let projects = this.dal.queryDb('select * from projects where id = $1', [req.params.id], res);
  }
}

const projectRouter = new ProjectRouter();
export default projectRouter.router;

为什么我不能从get和getOne函数访问“dal”对象。“this”关键字返回未定义的值

更改：

get(req: Request, res: Response, next: NextFunction) {
  let projects = this.dal.queryDb('select * from projects', null, res);
}

到

作为

与getOne相同

为什么我不能从get和getOne函数访问“dal”对象。“this”关键字返回未定义的值

更改：

get(req: Request, res: Response, next: NextFunction) {
  let projects = this.dal.queryDb('select * from projects', null, res);
}

到

作为

与getOne相同