假设我有这样的结构：
-users
-user1_uid
name
distance
age
我如何进行查询(查找距离<100且年龄介于20到25之间的用户)？ 我试过标准方法
let recentPostsQuery = (ref?.child("users").queryOrderedByChild("age").queryStartingAtValue("20"))!
问题是,这似乎不可能查询多个孩子(如结合年龄和距离过滤).几个月前与Firebase相比,这方面有什么变化吗？我相信,在第一次查询后在本地过滤它们不是一种选择,因为可能存在数千个对象.
我的第一选择是查询20到25之间的所有用户,然后在代码中过滤距离<1的用户. 100. 问题表明,代码中的过滤不是一种选择,但我想将其包含在完全适用于数千个节点或更少节点的情况中：
struct User { //starting with a structure to hold user data
var firebaseKey : String?
var theAge: Int?
var theDistance: Int?
}
var userArray = [User]() //the array of user structures
usersRef.queryOrderedByChild("age").queryStartingAtValue(20)
.queryEndingAtValue(25).observeEventType(.Value,withBlock: { snapshot in
for child in snapshot.children { //.Value so iterate over nodes
let age = child.value["age"] as! Int
let distance = child.value["distance"] as! Int
let fbKey = child.key!
let u = User(firebaseKey: fbKey,theAge: age,theDistance: distance)
userArray.append(u) //add the user struct to the array
}
//the array to contain the filtered users
var filteredArray: [User] = []
filteredArray = userArray.filter({$0.theDistance < 100}) //Filter it,baby!
//print out the resulting users as a test.
for aUser in filteredArray {
let k = aUser.firebaseKey
let a = aUser.theAge
let d = aUser.theDistance
print("array: \(k!) \(a!) \(d!)")
}
})
}
现在一个潜在的超简单答案.
let usersRef = self.myRootRef.childByAppendingPath("users")
usersRef.queryOrderedByChild("age").queryStartingAtValue(20)
.queryEndingAtValue(25).observeEventType(.ChildAdded,withBlock: { snapshot in
let distance = snapshot.value["distance"] as! Int
if distance < 100 {
let age = snapshot.value["age"] as! Int
let fbKey = snapshot.key!
print("array: \(fbKey) \(age) \(distance)")
}
})
请注意,我们正在利用.ChildAdded而不是.Value,因此每次读取一个节点 – 如果距离不是我们想要的,我们可以忽略它并继续下一个节点.