Angular2反应形式下拉菜单

Question

I am just learning angular 2 and have a case where I am creating a form that will be a piece of equipment. One of the fields that are associated with the equipment is a building. When the user is editing or adding a new piece of equipment I want them to be presented with a drop-down with a list of the building they can assign the equipment to. The equipment-detail component is as follows:

  export class EquipmentDetailComponent implements OnInit {
  equipment: IEquipment;
  equipmentForm: FormGroup;
  buildingList: Ibuilding[];

  constructor(private EquipmentService: EquipmentService,
              private BuildingsService: BuildingsService) { }

  ngOnInit() {
    this.equipment = this.EquipmentService.getEquipmentDetail(1);
    this.buildingList = this.BuildingsService.getBuildingList();

    let id = new FormControl(this.equipment.id);
    let unit = new FormControl(this.equipment.unit);
    let active = new FormControl(this.equipment.active);
    let building = new FormControl(this.equipment.building.id);

    this.equipmentForm = new FormGroup({
      id: id,
      unit: unit,
      active: active,
      building: building
    })    
  }

  saveEquipment(formValues){
    console.log(formValues);
  }

  onSelect(id){
    this.equipment.building = this.BuildingsService.getBuildingDetail(id);
    console.log(this.equipment.building)
  }
}

The equipment-detail html is as follows:

<div class="col-md-2">
  <form [formGroup]="equipmentForm" (ngSubmit)="saveEquipment(equipmentForm.value)" autocomplete="off" novalidate>
    <div class="form-group">
      <label form="unit">Unit:</label>
      <input formControlName="unit" id="unit" type="text" class="form-control" placeholder="Unit...."/>
    </div>
    <div class="form-group">
      <label form="active">Active:</label>
      <input formControlName="active" id="active" type="checkbox" class="form-control"/>
    </div>
    <div class="form-group">
      <label form="building">Building:</label>
      <select class="form-control" formControlName="building" (change)="onSelect($event.target.value)">
        <option *ngFor="let building of buildingList" value={{building.id}}>
          {{building.buildingName}}
        </option>
      </select>
    </div>
    <button type="submit" class="btn btn-primary">Save</button>
  </form>
</div>

When I click the dropdown option I get an object that represents the building that I selected. The result is

Object {id: 2, buildingName: "Building 2", active: true}
   active: true
   buildingName: "Building 2"
   id: 2

When I click the save button and look at the data that is associated with the formcontrol the building is no longer an object it is just the buildingId.

Object {id: 1, unit: "Item 1", active: true, building: "2"}
   active: true
   building: "2"
   id: 1
   unit:"Item 1"
   __proto__: Object

How do I get the main equipment object to be set with the building object and not just the building id?

Answer 1

It is because you had value attribute with building.id , that's why it is assigning building.id on option selection. You should consider changing your value attribute binding to ngValue with whole building object.

<select class="form-control" formControlName="building" (change)="onSelect($event.target.value)">
  <option *ngFor="let building of buildingList" [ngValue]="building">
    {{building.buildingName}}
  </option>
</select>