无法在firebase中

Question

我有像

这样的数据

{
"2017-11-01": {
"created_at": "2017-11-23 10:47:45",
"file_name": "qrcodes/1511434065790.png",
"qrvalue": "$2y$10$O8UcNz0TNvQdd3P3tfKNHe.OXVKC3KOQhtbZO9Sgl7x04sR.uTUhK",
"updated_at": "00-00-00 00:00:00",
"used": 1
},
"2017-11-21": {
"created_at": "2017-11-24 04:57:28",
"file_name": "qrcodes/15114994486172.png",
"qrvalue": "$2y$10$8QlU2d4o44YWw28h3pkAz.0EAclDxfAQfZQ6jR8VCAOznmdD5syPS",
"updated_at": "00-00-00 00:00:00",
"used": 2
},
"2017-11-24": {
"created_at": "2017-11-23 10:48:02",
"file_name": "qrcodes/15114340825347.png",
"qrvalue": "$2y$10$iiVr1FP4AYlAuhZEogSjMeeigjG1dMUnGm1A4XeK6EVF4HMogk2Lq",
"updated_at": "00-00-00 00:00:00",
"used": 0
}
}

并且我在规则中定义了indexOn“used”但是在执行orderBy =“used”时它没有相应的排序。如何按键值排序。