如何使用where子句删除Firebase中的对象？

Question

如果我在Firebase中有以下树结构，我该如何去除应该删除employeeid = (specified key)的所有班次？

"Shifts" : {
    "-KhJJMkElsuGRcgDgewb" : {
      "EndTime" : 1491973200,
      "ShiftId" : "-KhJJMkElsuGRcgDgewb",
      "StartTime" : 1491955200,
      "employeeid" : "UrjkB0QVJNTzSOHjDmxdyeecspG3"
    },
    "-KhJNv5itUJHhrxJlkLV" : {
      "EndTime" : 1491881400,
      "ShiftId" : "-KhJNv5itUJHhrxJlkLV",
      "StartTime" : 1491868800,
      "employeeid" : "SY6qNTB8EsbNoJ4qjQwX8goWmHE3"
    },
    "-KhJNwSHMn0Hfqtx81NJ" : {
      "EndTime" : 1492066800,
      "ShiftId" : "-KhJNwSHMn0Hfqtx81NJ",
      "StartTime" : 1492041600,
      "employeeid" : "UrjkB0QVJNTzSOHjDmxdyeecspG3"
    }
}

rootRef2 = firebase.database().ref().child("Shifts");
firebase.database().ref('Shifts')
      .orderByChild('employeeid')
      .equalTo(k)
      .limitToFirst(1)
      .once('value', snap => {
      rootRef2.child(k).remove();
      });