用httpClient实现内存中的角化web循环依赖

Question

我尝试使用angular-in-memory-web-api (0.5.1版)。如果我用本地对象设置“数据库”，这很好，但如果我试图通过http请求从本地JSON文件中获取数据，并出现以下错误，它就会失败：

未知错误:提供者解析错误:不能实例化循环依赖！HttpClient ("ERROR ->")：在./ AppModule @-1:-1中的NgModule AppModule中

一旦我将httpClient包导入到我的服务中。

app.module.ts：

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';
// Imports for loading & configuring the in-memory web api
import { HttpClientInMemoryWebApiModule } from 'angular-in-memory-web-api';
import { InMemoryDataService } from 'app/shared/services/in-memory-data.service';

import { AppComponent } from './app.component';
// other imports of app components

@NgModule({
  imports:      [
    BrowserModule,
    HttpClientModule,
    HttpClientInMemoryWebApiModule.forRoot(InMemoryDataService),    // always import after the HttpClientModule
  ],
  declarations: [
    AppComponent,
    // ...
  ],
  providers: [ // app wide services not concerning the problem ],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

内存中数据服务：

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { InMemoryDbService } from 'angular-in-memory-web-api';
import { RequestInfo } from 'angular-in-memory-web-api';

@Injectable()
export class InMemoryDataService implements InMemoryDbService {       
  // constructor(http: HttpClient) { // this creates the cyclic dependency
  constructor() {

  }    
  createDb(reqInfo?: RequestInfo) {
    const db = {}   
    // fetch data from local JSON files and set up "database" object    
    return db;
  }

}

这个问题是与HttpClientModule有关还是angular-in-memory-web-api问题？

Answer 1

我也面临着同样的问题，这就是我如何能够解决它，不要注入构造函数，而是尝试在方法中这样做。

在您的createDB中，您将正确地注入httpclient，而不会出现循环错误。

import { Injectable, Injector } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { InMemoryDbService } from 'angular-in-memory-web-api';
import { RequestInfo } from 'angular-in-memory-web-api';

@Injectable()
export class InMemoryDataService implements InMemoryDbService {  
  httpClient: HttpClient;
  constructor(private inject: Injector) {

  }    
  createDb(reqInfo?: RequestInfo) {
    const db = {}   
    this.httpClient = this.inject.get(HttpClient);
    // fetch data from local JSON files and set up "database" object    
    return db;
  }

}