Firebase queryOrderedByChild()方法不给出排序数据 [英] Firebase queryOrderedByChild() method not giving sorted data
问题描述
你好,我的数据库结构是这样的
{
users:{
alovelace:{
name:Ada Lovelace,
score:4,
},
ghopper:{...},
eclarke:{...}
}
}
我试图以降序的方式检索前20个分数。
let queryRef = FIRDatabase.database()。reference()。child (users)。queryOrderedByChild(score)。queryLimitedToLast(20)
queryRef.observeSingleEventOfType(.Value,withBlock:{(quearySnapShot)in
print(quearySnapShot.value)
} )
我正在试图获得输出,例如
< pre $ 得分:4
得分:3
得分:2
或
得分 :2
得分:3
得分:4
或
2
3
4
请让我知道如何解决这个问题。 使用方法 observeEventType
而不是 observeSingleEventOfType
。
另外,使FIRDataEventType为 ChildAdded
。
$ b $ p
最后,如果您想要Top 20项目,请使用 对于上面的数据集 key:ghopper,value:可选({ 键:alovelace,值:可选({ key:eclarke,value:可选({$ b $ name = Emily Clarke; 快照将以本机类型返回内容。 可选(4) 可选(5) 如果您想降序,您可以制作一些 技巧4> (4:40)。 Hi my database structure is some thing like this I am trying to retrieve top 20 scores in descending order. i am trying to get output like Please let me know how to solve this. Use method Last, If you want Top 20 items, use For the dataset above
key: ghopper, value: Optional({
name = Grace Hopper;
score = 2;
}) key: alovelace, value: Optional({
name = Ada Lovelace;
score = 4;
}) key: eclarke, value: Optional({
name = Emily Clarke;
score = 5;
}) Snapshot will returns the contents as native types.
Data types returned: So, you can get your scores this way.
Optional(2) Optional(4) Optional(5) Moreover, the default of realtime database return everything in ascending order. If you want descending order, you can make some tricks(4:40) in your database. 这篇关于Firebase queryOrderedByChild()方法不给出排序数据的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋! queryLimitedToFirst
而不是 queryLimitedToLast <
$ b $ {
用户:{
alovelace:{
name:Ada Lovelace,
得分:4
},
eclarke:{
name:Emily Clarke,
得分:5
},
ghopper:{
name:Grace Hopper,
score:2
}
let queryRef = FIRDatabase.database()。reference()。child(users)。queryOrderedByChild(score)。queryLimitedToFirst(20)
queryRef.observeEventType(.ChildAdded,withBlock:{(snapshot)in
print(key:\(snapshot.key),value:\(snapshot.value))
})
name = Grace Hopper;
score = 2;
})
name = Ada Lovelace;
分数= 4;
score = 5;
)
返回的数据类型:
所以,你可以得到你的分数是这样的。
$ b $ pre $ let queryRef = FIRDatabase.database()。reference()。child(users)。queryOrderedByChild (score)。queryLimitedToFirst(20)
queryRef.observeEventType(.ChildAdded,withBlock:{(snapshot)in
如果let scores = snapshot.value as?NSDictionary {
print(scores [score])
}
})
可选(2)
$ b {
"users": {
"alovelace": {
"name": "Ada Lovelace",
"score": 4,
},
"ghopper": { ... },
"eclarke": { ... }
}
}
let queryRef = FIRDatabase.database().reference().child("users").queryOrderedByChild("score").queryLimitedToLast(20)
queryRef.observeSingleEventOfType(.Value, withBlock: { (quearySnapShot) in
print(quearySnapShot.value)
})
score": 4
score": 3
score": 2
or
score": 2
score": 3
score": 4
or
2
3
4
observeEventType
instead of observeSingleEventOfType
.
Also, make FIRDataEventType to ChildAdded
. queryLimitedToFirst
instead of queryLimitedToLast
.{
"users" : {
"alovelace" : {
"name" : "Ada Lovelace",
"score" : 4
},
"eclarke" : {
"name" : "Emily Clarke",
"score" : 5
},
"ghopper" : {
"name" : "Grace Hopper",
"score" : 2
}
}
}
let queryRef = FIRDatabase.database().reference().child("users").queryOrderedByChild("score").queryLimitedToFirst(20)
queryRef.observeEventType(.ChildAdded, withBlock: { (snapshot) in
print("key: \(snapshot.key), value: \(snapshot.value)")
})
let queryRef = FIRDatabase.database().reference().child("users").queryOrderedByChild("score").queryLimitedToFirst(20)
queryRef.observeEventType(.ChildAdded, withBlock: { (snapshot) in
if let scores = snapshot.value as? NSDictionary {
print(scores["score"])
}
})