打字稿通用服务

Question

我是 typescript 和 angular2/4 的新手，我正在构建一个具有两个基本实体的应用程序，即 Car 和 Driver，我所做的只是通过 API 调用列出它们。

我面临的问题是每个 CarService 和 DriverService 都有代码冗余，而其他实体服务的代码可能相同。

目前的实现如下，跳过其他方法进行说明：

@Injectable()
export class CarService  {

private actionUrl: string;
private headers: Headers;

constructor(private _http: Http, private _configuration: Configuration) {

    // Getting API URL and specify the root
    this.actionUrl = _configuration.serverWithApiUrl + 'Car/';

    this.headers = new Headers();
    this.headers.append('Content-Type', 'application/json');
    this.headers.append('Accept', 'application/json');
}

// Function to get all Cars - API CALL: /
public GetAll = (): Observable<Car[]> => {
    return this._http.get(this.actionUrl)
        .map((response: Response) => <Car[]>response.json())
        .catch(this.handleError);
}

// Function to get a Car by specific id - API CALL: /:id
public GetSingle = (id: number): Observable<Car> => {
    return this._http.get(this.actionUrl + id)
        .map((response: Response) => <Car>response.json())
        .catch(this.handleError);
}

// Function to add a Car - API CALL: /create
public Add = (newCar: Car): Observable<Car> => {
    return this._http.post(this.actionUrl + '/create', JSON.stringify(newCar), { headers: this.headers })
        .catch(this.handleError);
}

// Function to update a Car - API CALL: /
public Update = (id: number, CarToUpdate: Car): Observable<Car> => {
    return this._http.put(this.actionUrl + id, JSON.stringify(CarToUpdate), { headers: this.headers })
        .catch(this.handleError);
}

// Function to delete a Car - API CALL: /:id
public Delete = (id: number): Observable<Response> => {
    return this._http.delete(this.actionUrl + id)
        .catch(this.handleError);
}

// Function to throw errors
private handleError(error: Response) {
    console.error(error);
    return Observable.throw(error.json().error || 'Server error');
}

DriverService 唯一改变的是 url 末尾的 Car/ 和 Observable<Car[]> 中的数据类型和响应。

我想知道使用通用服务避免这种情况的最佳方法是什么，以及如何在 Typescript 中做到这一点。

Answer 1

您可以创建一个抽象泛型类和两个继承自它的子类：

抽象类：

export abstract class AbstractRestService<T> {
  constructor(protected _http: Http, protected actionUrl:string){
  }

  getAll():Observable<T[]> {
    return this._http.get(this.actionUrl).map(resp=>resp.json() as T[]);
  }
  getOne(id:number):Observable<T> {
    return this._http.get(`${this.actionUrl}${id}`).map(resp=>resp.json() as T);
  }
} 

驱动服务类

@Injectable()
export class DriverService extends AbstractRestService<Driver> {
  constructor(http:Http,configuration:Configuration){
    super(http,configuration.serverWithApiUrl+"Driver/");
  }
}

汽车服务等级

@Injectable()
export class CarService extends AbstractRestService<Car> {
  constructor(http:Http,configuration:Configuration) {
    super(http,configuration.serverWithApiUrl+"Car/");
  }
}

请注意，只有具体类被标记为@Injectable()，并且应该在模块内声明，而抽象类不应该。

Angular 4+ 更新

Http 类被弃用以支持HttpClient，您可以将抽象类更改为类似的内容：

export abstract class AbstractRestService<T> {
  constructor(protected _http: HttpClient, protected actionUrl:string){
  }

  getAll():Observable<T[]> {
    return this._http.get(this.actionUrl) as Observable<T[]>;
  }

  getOne(id:number):Observable<T> {
    return this._http.get(`${this.actionUrl}${id}`) as Observable<T>;
  }
} 

Answer 2

以下是基于 Angular 7 和 RxJS 6 构建的基本示例。

ApiResponse<T> 代表任何服务器响应。服务器必须具有相同的结构，并且无论发生什么都返回它：

export class ApiResponse<T> {
  constructor() {
    this.errors = [];
  }
  data: T;
  errors: ApiError[];
  getErrorsText(): string {
    return this.errors.map(e => e.text).join(' ');
  }
  hasErrors(): boolean {
    return this.errors.length > 0;
  }
}

export class ApiError { code: ErrorCode; text: string; }

export enum ErrorCode {
  UnknownError = 1,
  OrderIsOutdated = 2,
  ...
}

通用服务：

export class RestService<T> {
  httpOptions = {
    headers: new HttpHeaders({ 'Content-Type': 'application/json', 
       'Accept': 'application/json'})
  };
  private _apiEndPoint: string = environment.apiEndpoint;
  constructor(private _url: string, private _http: HttpClient) { }

  getAll(): Observable<ApiResponse<T[]>> {
    return this.mapAndCatchError(
      this._http.get<ApiResponse<T[]>>(this._apiEndPoint + this._url
         , this.httpOptions)
    );
  }
  get(id: number): Observable<ApiResponse<T>> {
    return this.mapAndCatchError(
      this._http.get<ApiResponse<T>>(`${this._apiEndPoint + this._url}/${id}`
         , this.httpOptions)
    );
  }
  add(resource: T): Observable<ApiResponse<number>> {
    return this.mapAndCatchError(
      this._http.post<ApiResponse<number>>(
        this._apiEndPoint + this._url,
        resource,
        this.httpOptions)
    );
  }
  // update and remove here...

  // common method
  makeRequest<TData>(method: string, url: string, data: any)
                                    : Observable<ApiResponse<TData>> {
    let finalUrl: string = this._apiEndPoint + url;
    let body: any = null;
    if (method.toUpperCase() == 'GET') {
      finalUrl += '?' + this.objectToQueryString(data);
    }
    else {
      body = data;
    }
    return this.mapAndCatchError<TData>(
      this._http.request<ApiResponse<TData>>(
        method.toUpperCase(),
        finalUrl,
        { body: body, headers: this.httpOptions.headers })
    );
  }

  /////// private methods
  private mapAndCatchError<TData>(response: Observable<ApiResponse<TData>>)
                                         : Observable<ApiResponse<TData>> {
    return response.pipe(
      map((r: ApiResponse<TData>) => {
        var result = new ApiResponse<TData>();
        Object.assign(result, r);
        return result;
      }),
      catchError((err: HttpErrorResponse) => {
        var result = new ApiResponse<TData>();
        // if err.error is not ApiResponse<TData> e.g. connection issue
        if (err.error instanceof ErrorEvent || err.error instanceof ProgressEvent) {
          result.errors.push({ code: ErrorCode.UnknownError, text: 'Unknown error.' });
        }
        else {
          Object.assign(result, err.error)
        }
        return of(result);
      })
    );
  }

  private objectToQueryString(obj: any): string {
    var str = [];
    for (var p in obj)
      if (obj.hasOwnProperty(p)) {
        str.push(encodeURIComponent(p) + "=" + encodeURIComponent(obj[p]));
      }
    return str.join("&");
  }
}

那么你可以从RestService<T>派生：

export class OrderService extends RestService<Order> {
  constructor(http: HttpClient) { super('order', http); }
}

并使用它：

this._orderService.getAll().subscribe(res => {
  if (!res.hasErrors()) {
    //deal with res.data : Order[]
  }
  else {
    this._messageService.showError(res.getErrorsText());
  }
});
// or
this._orderService.makeRequest<number>('post', 'order', order).subscribe(r => {
  if (!r.hasErrors()) {
    //deal with r.data: number
  }
  else
    this._messageService.showError(r.getErrorsText());
});

您可以重新设计RestService<T>.ctor并直接注入RestService<Order>，而不是声明和注入OrderService。

看起来RxJS 6 不允许重新抛出/返回键入的错误。因此RestService<T> 捕获所有错误并在强类型ApiResponse<T> 中返回它们。调用代码应该检查ApiResponse<T>.hasErrors() 而不是在Observable<T> 上捕获错误

Answer 3

为您的应用提供基础服务。

使用 get post 和 delete 方法并附加您的 base URL。

export class HttpServiceBase {

    HOST_AND_ENDPOINT_START : string = 'you/rD/efa/ult/Url' ;
    public getWebServiceDataWithPartialEndpoint(remainingEndpoint: string): Observable<Response> {

        if (!remainingEndpoint) {
            console.error('HttpServiceBase::getWebServiceDataWithPartialEndpoint - The supplied remainingEndpoint was invalid');
            console.dir(remainingEndpoint);
        }

        console.log('GET from : ' , this.HOST_AND_ENDPOINT_START + remainingEndpoint);
        return this.http.get(
            this.HOST_AND_ENDPOINT_START + remainingEndpoint

        );
    }

这是一个有用的实现，因为它允许您轻松调试 WS 调用 - 所有调用最终都来自基础。

HOST_AND_ENDPOINT_START 可以被您想要扩展基础服务的任何模块覆盖。

让我们假设你的端点是这样的： /myapp/rest/

如果你想实现一个HttpSearchBase，你可以简单地扩展HttpServiceBase并用类似的东西覆盖HOST_AND_ENDPOINT_START：

/myapp/rest/search

例如CarDriverService

@Injectable()
export class CarDriverService extends HttpServiceBase{

    //here we are requesting a different API
    HOST_AND_ENDPOINT_START : string = '/myapp/rest/vehicle/;
    getAllCars() : Observable<Car[]>{
    return this.getWebServiceDataWithPartialEndpoint('/Car')
           .map(res => <Car[]>res.json())
    }

    getAllDrivers(){
    return this.getWebServiceDataWithPartialEndpoint('/Driver')
    }

    addNewDriver(driver: Driver){
    return this.postWebServiceDataWithPartialEndpoint('/Driver/',driver)
    }


}