Formarray doesnt show all the records received from service/api

问题

I am trying to patch the object received from webapi to an angular reactive form. The form also has a formarray. But, despite having more than 3 or more records only 2 records are being patched to the formarray of the reactive form.

I have two entities noseries and noseriesList, where a noseries has zero or many noseriesLists. So after obtaining noseries from webapi, i want to patch properties and navigation list "noseriesLists" of noseries into reactive form. Rest of the properties are being patched properly, but only 2 records of navigation list "noseriesLists" is being patched to the formArray nested inside the reactive form.

//initialization of form
    this.noseriesForm = this.fb.group({
      id: [null],
      description: ['', Validators.required],
      code: [ '', Validators.compose([Validators.maxLength(10), Validators.required])],
      noSeriesList: this.fb.array([
         this.initLine(), this.initLine()
      ])
    });

//patching the object received from service to form
 this.route.params.subscribe(routeParam => {
      if (routeParam.id) {
        this.noseriesService.get(routeParam.id)
        .subscribe((data: NoSeries) => {
          this.isCreateMode = false;
          this.noseries = data;
          this.noseriesForm.patchValue(this.noseries);
          console.log(this.noseries, 'data from api');
          console.log(this.noseriesForm.value,'formvalue');
        });
      }

    });

//initialise formArray
  initLine(): FormGroup {
    return this.fb.group({
      id: [null],
      startingNoSeries: ['', Validators.required],
      endingNoSeries: '',
      lastUsedSeries: '',
      effectiveDate: [null],
      endingDate: [null],
      noSeriesId: [null]
    });
  }

logging the data received from service shows 3 noseriesList records, whereas logging formvalue only shows 2 records of noseriesList.

回答1:

while you are initializing the form array for the first time you are adding two empty controls. that's why when you patch value to formgroup, only those two empty controls get filled. you should fill the formarray with number of controls that is going to be patched before patching a value.

//patching the object received from service to form
this.route.params.subscribe(routeParam => {
    if (routeParam.id) {
        this.noseriesService.get(routeParam.id).subscribe((data: NoSeries) => {
          this.isCreateMode = false;
          this.noseries = data;

          const nsList = this.noseriesForm.get("noSeriesList") as FormArray;
          nsList.clear();
          this.noseries.forEach(_ => nsList.push(this.initLine()));

          this.noseriesForm.patchValue(this.noseries);
          console.log(this.noseries, 'data from api');
          console.log(this.noseriesForm.value,'formvalue');
        });
    }

});

来源：https://stackoverflow.com/questions/56616822/formarray-doesnt-show-all-the-records-received-from-service-api