updateChildValues：不保存所有数据

Question

用户输入带有一些标签的帖子。标签以数组的形式返回，我应该检查标签是否已经存在，并使用tagID将其写入post数据库，以便标签与post相关（见下文）。现在发生的事情只是最后一个tagID被记录到数据库而不是所有这些

for item in tags {

    ref.child("tags").observeSingleEventOfType(.Value, withBlock: { snapshot in
        if snapshot.childSnapshotForPath(item.lowercaseString).exists() {
            let tagKey = snapshot.childSnapshotForPath(item.lowercaseString).value as! String
            self.saveTagID(tagKey, postKey: Postkey, UID: userID)

        } else {
            let tagKey = self.ref.child("tags").childByAutoId().key
            let tagUpdate = ["/tags/\(item.lowercaseString)": tagKey]
            self.ref.updateChildValues(tagUpdate)

            self.saveTagID(tagKey, postKey: Postkey, UID: userID)

        }
    })
}

func saveTagID(tagID: String, postKey: String, UID: String){

    let postTag = [tagID: true]
    print("post tag\(postTag)")
    ref.updateChildValues(["posts/\(postKey)/tagIDs": postTag,
        "user-posts/\(UID)/\(postKey)/tagIDs": postTag])
}

这就是数据库的样子。在tagID中，如果只有一个标签

，则应该只有一个

{
    "posts": {
        "-KNlBs1EC6tkfLA2y4Sc": {
            "author": "Michele",
            "post": "Hello human",
            "tagIDs": {
                "-KNlBs76y5I0KDV1OXS_": true
            },
            "tagNames": "test, hope this works",
            "uid": "QGacTE84GBSC7uuN4wemxCdHXWo2"
        },
        "-KNlCB1CACxXPLpYc5ql": {
            "author": "Michele",
            "post": "You're my only hope",
            "tagIDs": {
                "-KNlCB723ScwIhYDuwRn": true
            },
            "tagNames": "help, Obi wan",
            "uid": "QGacTE84GBSC7uuN4wemxCdHXWo2"
        }
    },
    "tags": {
        "help": "-KNlCB71o5L2PhdQdl62",
        "hope this works": "-KNlBs76y5I0KDV1OXS_",
        "obi wan": "-KNlCB723ScwIhYDuwRn",
        "test": "-KNlBs7509HQ29waf8Ms"
    }
}