Angular 7 rxjs/forkJoin : You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable

Question

logic component.js file in below.

ngOnInit() {  
   const join= forkJoin( this.getReconciliationData()); //import { forkJoin } from 'rxjs/internal/observable/forkJoin';
   const subscribe= join.subscribe(result=>this.setReferenceTableData()); //Getting issue here
  }
  getReconciliationData() {
    this.commonService.getMasterData(MaterDataType.LOCALREFERENCES).subscribe(result=>{
      this.categories=result;
      this.categories.forEach(c => {
        c.children.forEach(subC => {
          this.references.push(...subC.references);
        });
        this.subCategories.push(...c.children);
      });
    });

  }
  setReferenceTableData=function(){
    this.dataSource=new MatTableDataSource(this.references);
  }

While execution time getting an error.

***core.js:7187 ERROR TypeError: You provided 'undefined' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.
    at Object.push../node_modules/rxjs/internal/util/subscribeTo.js.exports.subscribeTo (subscribeTo.js:29)
    at Object.from (from.js:11)
    at _loop_1 (forkJoin.js:42)
    at Observable._subscribe (forkJoin.js:67)
    at Observable.push../node_modules/rxjs/internal/Observable.js.Observable._trySubscribe (Observable.js:44)
    at Observable.push../node_modules/rxjs/internal/Observable.js.Observable.subscribe (Observable.js:30)
    at MedicalfileInternalServiceModelComponent.ngOnInit (medicalfile-internal-service-model.component.ts:69)
    at checkAndUpdateDirectiveInline (core.js:24503)
    at checkAndUpdateNodeInline (core.js:35163)
    at checkAndUpdateNode (core.js:35102).***

. I Think here looking return object from getReconciliationData() function. But in my case not required return statement. Anyone please help us for this issue. I need to one by one function execution.

Answer 1

forkJoin expects array.

Try like this:

const join= forkJoin( [this.getReconciliationData()])

Answer 2

Try like below modified code . And i don't think you need forkJoin since you have only one observable

  ngOnInit() {
    const subscribe = this.getReconciliationData().subscribe(result => {
      this.categories = result;
      this.categories.forEach(c => {
        c.children.forEach(subC => {
          this.references.push(...subC.references);
        });
        this.subCategories.push(...c.children);
      });
      this.setReferenceTableData();
    }
  };

  getReconciliationData(): Observable<any> {
    return this.commonService.getMasterData(MaterDataType.LOCALREFERENCES);

  }
  setReferenceTableData=function(){
    this.dataSource=new MatTableDataSource(this.references);
  }

Answer 3

Your getReconciliationData() method returns nothing and it should return an Observable which you want to pass to the forkJoin() method. But are you sure you need to use it when you have only one thing to subscribe to?