var x = this.af.list('/pedidos/', ref => ref.limitToLast(1500));
  x.snapshotChanges().pipe(
      map(actions =>
        actions.map(a => ({key:a.key, ...a.payload.val()}))

        )
    ).subscribe(items => {


      })



      this.dataSource = new MatTableDataSource(items);
      this.dataSource.paginator = this.paginator;
      this.dataSource.sort = this.sort;

      });

    }