ngFor can only iterate over an array, It means that the result has to be an array! it cannot be undefined or null which are not iterable.

so when using ngFor you need to have either an empty array or a populated array.

Make sure your service properly returns an array by console loggin’ the result.

this.serviceCovid.recupererHistorique(his.id).subscribe(histo => console.log(histo));

If your service may return undefined compare your value to an empty array.

historique: Historique[] = [];

ok it worked
i had the wrong id it his.idCitoyen not his.id

 surChangementHistorique(his: Historique){
    this.serviceCovid.recupererHistorique(his.idCitoyen).subscribe(histo => this.historique = histo);

ngFor only supports Iterables such as Array, so you cannot use it for Object.

I keep getting this error and I don’t know what to do:
ERROR Error: Cannot find a differ supporting object ‘[object Object]’ of type ‘object’. NgFor only supports binding to Iterables such as Arrays

this is my service

 recupererHistorique(idCitoyen:number): Observable<Historique[]>{ 

    let url = 'http://localhost/tpSyn/getHistoriqueCitoyen.php?idCitoyen=' + idCitoyen;
    return this.http.get<Historique[]>(url); 
  } 
  

this is the component

export class HistoriqueComponent implements OnInit {

  
 @Input() historiquee:Historique;
 historique: Historique[]; 
 selectionActive:boolean = true;
 
  constructor(private serviceCovid: CovidTraceService) { }

  ngOnInit(): void {
  }

  surChangementCitoyen(){
    
  //this.historiquee = null;
  

  }

  
  surChangementHistorique(his: Historique){
    this.serviceCovid.recupererHistorique(his.id).subscribe(histo => this.historique = histo);
    
  
  }
 
}

And the HTMl

  <section *ngIf="historiquee" >
    
    <div >
        <ol >
            <li *ngFor='let hiss of historiquee'> {{hiss.date}}: {{hiss.description}} </li>
        </ol>
    </div>

     
    </section>

In the HTML if i use this instead it works but it shows one line and i want it to show all of the other lines thats why i want to use a *ngFor

  <div>
            <ol>
                <h3>
                    <li> {{historiquee.date}}: {{historiquee.description}} </li>
                </h3>

            </ol>
        </div>