Angular HttpClient返回undefined而不是数组

Question

所以我有一个API（返回JSON）设置，它打印出一条消息，提示用户正在获取用户，但我的console.log数据角度返回未定义...用例是否必须使用接口还是像我完全正常使用的模型？

如果您还检查我的错误处理并指出错误，则奖励积分。

我的后端服务ts：

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders, HttpResponse } from '@angular/common/http';
import { environment } from '../../../environments/environment';
import { Observable, of } from 'rxjs';
import { catchError, map, tap } from 'rxjs/operators';
import { User } from '../models/user.model';

const SERVICE_URL = 'http://localhost:3000/';

@Injectable()

export class AviorBackendService {

  constructor(private client: HttpClient) { }
  UserData: any;

  httpOptions = {
    headers: new HttpHeaders({ 'Content-Type': 'application/json' })
  };
/**
 * Handle Http operation that failed.
 * Let the app continue.
 * @param operation - name of the operation that failed
 * @param result - optional value to return as the observable result
 */
  private handleError<T>(operation = 'operation', result?: T) {
    return (error: any): Observable<T> => {

      // TODO: send the error to remote logging infrastructure
      console.error(error); // log to console instead

      // TODO: better job of transforming error for user consumption
      this.log(`${operation} failed: ${error.message}`);

      // Let the app keep running by returning an empty result.
      return of(result as T);
    };
  }

  /**
   * Log a failed AviorBackend error.
   * @param message - message of the operation that failed
   */
private log(message: string) {
  throw new Error(`AviorBackend: ${message}`);
}

  getUserCollection() {
    return this.client.get<User[]>(SERVICE_URL + 'users');
  }
  // Get user
  getUser(firstname: User): Observable<any> {
    const API_URL = `${SERVICE_URL}user/firstname/${firstname}`;
    return this.client.get(API_URL, this.httpOptions).pipe(
      map((res: Response) => {
        return res || {};
      }),
      catchError(this.handleError())
    );
  }

 /*  addUser() {
    return this.client.post(SERVICE_URL + 'user', this.UserData, this.httpOptions);
  } */

  // Add student
  addUser(data: User): Observable<any> {
    const API_URL = `${SERVICE_URL}user`;
    return this.client.post(API_URL, data)
      .pipe(
        catchError(this.handleError())
      );
  }


  // Update User
  putUser(loginId, data: User): Observable<any> {
    const API_URL = `${SERVICE_URL}update/${loginId}`;
    return this.client.put(API_URL, data, this.httpOptions).pipe(
      catchError(this.handleError())
    );
  }
  // Delete student
  deleteUser(id): Observable<any> {
    const API_URL = `${SERVICE_URL}delete-student/${id}`;
    return this.client.delete(API_URL).pipe(
      catchError(this.handleError())
    );
  }
}

我的用户模型ts：

import { Role } from './role';

export class User {
    id?: number;
    mandator?: number;
    loginId?: string;
    lastName?: string;
    firstName?: string;
    password?: string;
    eMail?: string;
    group: string;
    role: Role;
    active?: boolean;
    token?: string;
}

我的用户组件ts：

import { Component, OnInit } from '@angular/core';
import { AviorBackendService } from '../services/avior-backend.service';
import { UserCollection } from '../models/user-collection.model';
import { User } from '../models/user.model';

@Component({
  selector: 'app-users',
  templateUrl: './users.component.html',
  styleUrls: ['./users.component.css']
})
export class UsersComponent implements OnInit {

  selectedItem: string;

  users: UserCollection;
  user: User;
  firstname: string;
  selectedUser: User;

  constructor(private aviorBackend: AviorBackendService) { }

  ngOnInit() {
      this.aviorBackend.getUserCollection().subscribe(data => {
      // tslint:disable-next-line: no-string-literal
      this.users = data['users'];
      console.log(this.users);
    });
  }

  clickItem(firstname) {
      this.aviorBackend.getUser(firstname).subscribe(data => {
      // tslint:disable-next-line: no-string-literal
      this.selectedUser = data['user'];
      console.log(this.selectedUser);
    });
  }
}

<div class="list-area">

  <div class="col-lg-12">

    <p class="list-header">Element overview</p>

    <div class="form-group">
      <label for="filter" class="lb-sm">Filter</label>
      <input type="text" class="form-control input-sm" name="filter" id="filter">
    </div>

   <select size="20" multiple class="form-control" id="elementlist" [(ngModel)]="selectedItem" (click)="clickItem(firstname)">
      <option *ngFor="let user of users">
        {{user?.lastName}}, {{user?.firstName}}
      </option>
    </select>

  </div>

</div>

<div class="content-area">

  <div class="col-lg-12" *ngIf="selectedUser?.id">

  <p>Element contents {{selectedUser?.id}}</p>

  <div class="col-lg-12">
    <div class="form-group">
      <label for="firstName" class="lb-sm">First name</label>
      <input type="text" class="form-control input-sm" name="firstName" id="firstName" [(ngModel)]="selectedUser.firstName">
    </div>
  </div>

  </div>

</div>

更新

我的user-collection.model.ts：

import { User } from './user.model';

export class UserCollection {

    user: User[];

}