Question

当我想在evenement组件中显示Medecin数据的用户类的标签“ Nom”时，我收到此错误消息：

RROR TypeError: Cannot read property 'Users' of undefined
at Object.eval [as updateRenderer] (EvenementComponent.html:34)
at Object.debugUpdateRenderer [as updateRenderer] (core.js:36078)
at checkAndUpdateView (core.js:35061)
at callViewAction (core.js:35421)
at execEmbeddedViewsAction (core.js:35378)
at checkAndUpdateView (core.js:35056)
at callViewAction (core.js:35421)
at execEmbeddedViewsAction (core.js:35378)
at checkAndUpdateView (core.js:35056)
at callViewAction (core.js:35421)

这是我的代码：

evenement.component.html：

<ng-template pTemplate="header">
      <tr>
          <th>Medecin</th>                   
      </tr>
 </ng-template> 

 <ng-template pTemplate="body" let-rowData let-evenement >
       <tr [pSelectableRow]="rowData">   
            <td>{{evenement.Medecin.Users.Nom}}</td>                 
       </tr>
 </ng-template>

evenement.component.ts：

evenement: Evenement = new Evenement();
evenements: Evenement[] = [new Evenement()];
Users: User[];
Medecins: Medecin[];

constructor(private router: Router, private evenementService: EvenementService, private http: HttpClient, private messageService: MessageService) {

    this.evenementService.GetMedecins().subscribe(medecins => this.Medecins = medecins);

}
ngOnInit() {
    // console.log(this.evenements);
    this.evenementService.GetEvenements().subscribe(evenements => this.evenements = evenements);}

Evenement.ts：

export class Evenement {
constructor() {
    this.Medecin = new Medecin();
    this.Users = new User();
   }
Id: number;
Prix: number;
Medcin_Id: number;
Medecin: Medecin;
Users: User;}

Medecin.ts：

export class Medecin {
constructor() {
 this.Users = new User();

}
Id: number;
Users_Id: number;
Users: User;}

User.ts：

export class User {

Id: number;
Nom: string;
Prenom: string;   }

那么，有实施上的问题吗？我做错了吗？

Answer 1

您可以使用安全的导航操作符?.

<td>{{evenement?.Medecin?.Users?.Nom}}</td>

Answer 2

由于某些原因，该错误告诉我“用户”集合未定义（没有值），请尝试将初始化代码移到ngOnInit for Environment类中，看看是否可行。

如果这不起作用，则将断点或控制台日志登录到Mementin.ts，Evenement.ts和evenement.component.ts的ngOnInit的构造函数中。您将知道为什么它具有未定义的值。

evenement: Evenement;
evenements: Evenement[];
Users: User[];
Medecins: Medecin[];

constructor(private router: Router, private evenementService: EvenementService, private http: HttpClient, private messageService: MessageService) {

    this.evenementService.GetMedecins().subscribe(medecins => this.Medecins = medecins);

}
ngOnInit() {
    // console.log(this.evenements);
    Evenement = new Evenement();
    Evenement[] = [new Evenement()];    
    this.evenementService.GetEvenements().subscribe(evenements => this.evenements = evenements);
}

错误TypeError：无法读取未定义的属性“用户”

2 个答案: