打字稿通用服务

Question

我是打字稿和angular2 / 4的新手，我正在建立一个有两个基本实体的单一应用程序，即Car和Driver，我所做的就是用API调用列出它们。

我面临的问题是我为每个CarService和DriverService都有代码冗余，而且我可能为其他实体服务提供相同的代码。

到目前为止，实现方法正在遵循，其他方法也不再使用ilustration：

@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');
}

仅使用DriverService更改的是网址末尾的Car/和Observable<Car[]>中的数据类型以及响应。

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中进行此操作。

Answer 1

您可以创建一个抽象泛型类和两个继承它的子类：

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);
  }
} 

驱动程序服务类

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

汽车服务类

@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。

更新Angular 4 +

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

为您的应用提供基本服务。

使用附加get的{​​{1}} post和delete方法。

base URL

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。

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 ); } 可以被任何要扩展基本服务的模块覆盖。

让我们假装你的端点是这样的： HOST_AND_ENDPOINT_START

您希望实施/myapp/rest/，只需扩展HttpSearchBase并覆盖HttpServiceBase，例如：

HOST_AND_ENDPOINT_START

示例/myapp/rest/search

CarDriverService

Answer 3

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，然后将其返回：

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,
  ...
}

一般服务：

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>();
        Object.assign(result, err.error)
        // if err.error is not ApiResponse<TData> e.g. connection issue
        if (result.errors.length == 0) {
          result.errors.push({ code: ErrorCode.UnknownError, text: 'Unknown 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("&");
  }
}

那么您可以从RestService<T>派生出来：

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>，而不用声明和注入OrderService。

看来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。调用代码应检查ApiResponse<T>.hasErrors()而不是捕获Observable<T>上的错误