嵌套函数调用不起作用（代码流问题）

Question

我的代码存在问题：

问题在于：

如果param.qtamodificata == false，代码运行正常，但如果params.qtamodificata == true（并调用getQuantities函数），则由于异步调用而返回“undefined”...

我需要以同步方式设置代码流，以便仅在所有过程完成后才返回结果...

如何解决？

感谢支持

getOrderRow

public getOrderRow(params): Observable<any>
  {
    //OFFLINE SWITCH OK
    var res = { headers: [], data: [] }

    return Observable.fromPromise(this._WebDBService.sysConfigurazione.toArray().then(
      data => {

        var art = JSON.parse(data[0].ordinidatajson).filter(
          function(itm,index){
            return itm.codart.v === params.codart;
          }
        );

        res.headers = JSON.parse(data[0].ordiniheaderjson);

        if(params.qtamodificata == true)
        {
          this.getQuantities(art[0].codart.v,null,params.udmmodificata, params['qtaord'+ params.udmmodificata]).subscribe(
            qtys =>{
                  art[0].qtaord1.v = qtys.dqta1;
                  art[0].qtaord2.v = qtys.dqta2;
                  art[0].qtaord3.v = qtys.dqta3;

                  res.data = art[0];

                  return res;
                }
              );          
        }
        else
        {
          res.data = art[0];
          return res;
        }                         
      }
    ));
  }

getQuantities

public getQuantities(codart: string, codvar: string, idqta: number, qta: number): Observable<any>{

    return Observable.fromPromise(this._WebDBService.tbArticoli.where({codart: codart}).toArray().then(
      data => 
      {
        console.log('getQuantities');               

        var qtys = {
          dqta1: 0,
          dqta2: 0,
          dqta3: 0
        }

        var a = data[0];

        switch (idqta) {
          case 1:
            qtys.dqta1 = +qta;
            if (a.rapudm12 > 0 && a.codudm2)
              qtys.dqta2 = qta / a.rapudm12;
            if (a.rapudm23 > 0 && a.codudm3)
              qtys.dqta3 = qta / a.rapudm23;
            break;
          case 2:
            qtys.dqta2 = +qta;
            if (a.rapudm12 > 0 && a.codudm1)
              qtys.dqta1 = qta / a.rapudm12;
            if (a.rapudm23 > 0 && a.codudm3)
              qtys.dqta3 = qta / a.rapudm23;
            break;
          case 3:
            qtys.dqta3 = +qta;
            if (a.rapudm23 > 0 && a.codudm2)
              qtys.dqta3 = qta / a.rapudm23;
            if (a.rapudm12 > 0 && a.codudm1)
              qtys.dqta1 = qta / a.rapudm12;
            break;
        }
        return qtys;

      }));    
  }

函数调用

this.orderService.getOrderRow(params, 'test')
          .subscribe(list => {
            console.log('onlineorder3');
            console.log(list);
            console.log('onlineorder3');
}