Firebase如何检查快照的子代本身是否为Datasnapshot类型

Question

How can I check if the child LojqctqkDpthbF_TYvP has children that are other Datasnapshot s and not k/v pairs like in eg. 1 ?

I tried all of these but none worked:

Database.database().reference().child("LojqctqkDpthbF_TYvP").observeSingleEvent(of: .value, with: { (snapshot) in

    if !snapshot.hasChildren() { return }

    guard snapshot.children.allObjects is [DataSnapshot] else { return }

    guard let children = snapshot.children.allObjects as? [DataSnapshot] else { return }

    print("this print statement should only get reached if there are Datasnapshots underneath of it")

})

In the above code (from eg. 1 below) the print statement gets reached because there are children but they are only dict values. I want it so that the it doesn't get reached specifically because there aren't any Datasnapshots underneath of it.

eg. 1 Children that are dict values and no Datasnapshots

-LojqctqkDpthbF_TYvP
  |
  |---"key1":"value1"
  |---"key2":"value2"
  |---"key3":"value3"

The print statement should only get reached if there are Datasnapshots like in eg. 2 below

eg. 2 Children that are dict values and 2 Datasnapshots

-LojqctqkDpthbF_TYvP
  |
  |---"key1":"value1"
  |---"key2":"value2"
  |---"key3":"value3"
  |
  @-LlzB3_ppHHVmdipXs
  |     
  @-LlzD8p5-WOT-ZZhfc

Answer 1

You're using definitions that are slightly off, which makes it hard to implement.

Let's first set the correct definition of what data in the database becomes a DataSnapshot in the client:

Say you have this JSON in the database:

"-LojqctqkDpthbF_TYvP": {
  "key1": "value1",
  "key2": "value2",
  "key3": "value3"
}

If you load this JSON from the database into the app, you get a single top-level snapshot with key -LojqctqkDpthbF_TYvP . This snapshot has three child snapshots, one for each key under it. The fact that the value of each of those keys is a primitive string value, doesn't matter: they're still each a DataSnapshot . So in the above JSON there are four snapshots, with keys -LojqctqkDpthbF_TYvP , key1 , key2 , and key3 .

---

The difference is in the type of the value of the child DataSnapshot s. So if you want to know if he value of a certain DataSnapshot is itself a complex type again, you can do something like for each child snapshot :

snapshot?.value is Dictionary

Alternatively you can check for each child snapshot whether they have children:

snapshot?.hasChildren()

For -LojqctqkDpthbF_TYvP the above tests will both be true, while for the other keys they'll be false.