Question

我创建了如下所示的通用数据服务：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';

import { environment } from '../../../environments/environment';
import { Resource } from '../models/resource';

const API_URL = environment.apiUrl;

@Injectable()
export class DataService<T extends Resource> {

  constructor(
    private httpClient: HttpClient,
    private endpoint: string) {}

  public create(item: T): Observable<T> {
    return this.httpClient
      .post<T>(`${API_URL}/${this.endpoint}`, item);
  }

  public update(item: T): Observable<T> {
    return this.httpClient
      .put<T>(`${API_URL}/${this.endpoint}/${item.id}`, item);
  }

  read(id: number): Observable<T> {
    return this.httpClient
      .get(`${API_URL}/${this.endpoint}/${id}`)
      .map(response => response as T);
  }

  list(): Observable<T[]> {
    return this.httpClient
      .get(`${API_URL}/${this.endpoint}`)
      .map(response => response as T[]);
  }

  delete(id: number) {
    return this.httpClient
      .delete(`${API_URL}/${this.endpoint}/${id}`);
  }
}

然后我创建了一个 CategoryService 来扩展此功能：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

import { DataService } from './data.service';
import { Category } from '../models/category';

@Injectable()
export class CategoryService extends DataService<Category> {

  constructor(httpClient: HttpClient) {
    super(
      httpClient,
      'categories'
    );
  }

}

因此，现在我可以使用该服务的所有CRUD方法了。从那以后，我创建了许多其他服务，每个服务都扩展了DataService。问题是，我遇到了与返回类型不匹配的API端点。例如，端点“ / categories”，我的数据服务希望所有端点返回一个实体，该实体属于类别：

import { Resource } from "./resource";

export class Category extends Resource {
    name: string
}

但是，类别API有一个端点，该端点返回问题的列表。该路径是“ / categories / 2 / questions”。如何使它与我的通用数据服务一起使用？我想答案是我不能，但是必须有一种解决方法，也许是在每次调用而不是实例化时提供模型类型？

任何帮助将不胜感激。我希望这是有道理的。

Answer 1

听起来这条新路线并不通用。我认为CategoryService应该是实现新方法的类。

export class CategoryService extends DataService<Category> {

  constructor(httpClient: HttpClient) {
    super(
      httpClient,
      'categories'
    );
  }

  getQuestions(id: number): Observable<Question[]> {
    return this.httpClient
      .get<Question[]>(`${API_URL}/${this.endpoint}/${id}/questions`);
  }
}

您可以通过将其访问修饰符更改为endpoint来获得对httpClient和protected的引用

Answer 2

我决定删除通用服务，而改用通用方法。因此，数据服务成为（请注意新的query方法：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';

import { environment } from '../../../environments/environment';

const API_URL = environment.apiUrl;

@Injectable()
export class DataService {

  constructor(
    private httpClient: HttpClient,
    private endpoint: string) {}

  create<T>(item: T): Observable<T> {
    return this.httpClient
      .post<T>(`${API_URL}/${this.endpoint}`, item);
  }

  update<T>(item: T): Observable<T> {
    return this.httpClient
      .put<T>(`${API_URL}/${this.endpoint}/${item.id}`, item);
  }

  read<T>(id: number): Observable<T> {
    return this.httpClient
      .get(`${API_URL}/${this.endpoint}/${id}`)
      .map(response => response as T);
  }

  list<T>(): Observable<T[]> {
    return this.httpClient
      .get(`${API_URL}/${this.endpoint}`)
      .map(response => response as T[]);
  }

  query<T>(path: string): Observable<T[]> {
    return this.httpClient
      .get(`${API_URL}/${this.endpoint}/${path}`)
      .map(response => response as T[]);
  }

  delete(id: number) {
    return this.httpClient
      .delete(`${API_URL}/${this.endpoint}/${id}`);
  }
}

我的类别服务变为：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';

import { DataService } from './data.service';

@Injectable()
export class CategoryService extends DataService {

  constructor(httpClient: HttpClient) {
    super(
      httpClient,
      'categories'
    );
  }

}

要获取我的“类别问题”，我可以这样做：

this.categoryService.query<Question>(`${this.category}/questions`);

具有不同返回类型的通用数据服务

2 个答案: