Typescript 如何在控制器中使用服务？-快速打字脚本

这是ExpressTypeScript代码。我试图使用服务从数据库中获取数据，但遇到以下错误：

无法读取未定义的属性“populationService”

Controller.ts=>

import { PopulationService } from "../services/population.service";

export class PopulationController implements IController {
public path: string = "/population";
public router = Router();

private populationService: PopulationService = new PopulationService();

constructor() {
    this.initializeRoutes();
}

private initializeRoutes() {
    this.router.get(`${this.path}/getEmployer`, this.getEmployer);
}

private async getEmployer(request: Request, response: Response, next: NextFunction) {
    try {
        let result = await this.populationService.getEmployerFromService();
        return response.status(200).send(result);
    }
    catch (error) {
        next(error);
    }
}
}

import { pool } from "../../config/database";

export class PopulationService {

    public async getEmployerFromService(): Promise<any> {
        let sql = `SELECT * FROM population;`;
        let result = await pool.query(sql);
        return result.rows;
    }
}

Service.ts=>

import { PopulationService } from "../services/population.service";

export class PopulationController implements IController {
public path: string = "/population";
public router = Router();

private populationService: PopulationService = new PopulationService();

constructor() {
    this.initializeRoutes();
}

private initializeRoutes() {
    this.router.get(`${this.path}/getEmployer`, this.getEmployer);
}

private async getEmployer(request: Request, response: Response, next: NextFunction) {
    try {
        let result = await this.populationService.getEmployerFromService();
        return response.status(200).send(result);
    }
    catch (error) {
        next(error);
    }
}
}

import { pool } from "../../config/database";

export class PopulationService {

    public async getEmployerFromService(): Promise<any> {
        let sql = `SELECT * FROM population;`;
        let result = await pool.query(sql);
        return result.rows;
    }
}

从“../../config/database”导入{pool}”；
导出类填充服务{
公共异步getEmployerFromService（）：承诺{
让sql=`SELECT*FROM population；`；
让result=wait pool.query（sql）；
返回result.rows；
}
}

---

这有什么问题？我使用new关键字在controller中使用service，但仍然出现此错误。

因为您将

this.getEmployer

作为一个直接向上的函数传递，所以对

this

的引用丢失。有很多方法可以解决这个问题，但我喜欢这种方法（在类构造函数中）：

constructor（）{
this.getEmployer=this.getEmployer.bind（this）；
this.initializeRoutes（）；
}

我们还有另一个选择，那就是我们可以使用make-it-as-arrow函数

private getEmployer = async (request: Request, response: Response, next: NextFunction) => {
        let result = await this.populationService.getEmployerFromService();
        return response.status(200).send(result);
 }

---

但我不知道这是否是一个完美的解决方案。如果您有更好的解决方案，请在此处添加。

否@Evert，此操作不起作用，仍然会出现相同的错误，请给出任何其他建议