Android Firebase从未知键获取子节点并映射至heartScore对象的方法

Got it, let's break down how to solve this. You're working with a Firebase Realtime Database structure where each user has timestamped quiz entries, and you want to pull those entries (even though the timestamp keys are unknown upfront) and convert them into your custom heartScore objects. Here's how to implement this across common platforms:

Android (Java) #

First, make sure your heartScore class meets Firebase's requirements for object mapping:

• It has a no-argument constructor
• Member variable names match the database keys exactly (or use @PropertyName annotations if you prefer camelCase in code, e.g., @PropertyName("exercise_total") private String exerciseTotal;)
• Optional: Add a timestamp field to store the key of each entry

Here's the code to fetch and map the data:

// Get reference to the specific user's quiz entries
DatabaseReference userQuizRef = FirebaseDatabase.getInstance()
        .getReference("users") // Adjust this to your root node name if needed
        .child("-EvcKZHBZ4CVo9yAdlP7ldadCZS03");

// Listen for changes (or use get() for one-time fetch)
userQuizRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        List<heartScore> userQuizEntries = new ArrayList<>();
        
        // Iterate through all timestamped child nodes
        for (DataSnapshot timestampSnapshot : dataSnapshot.getChildren()) {
            // Map the snapshot directly to your heartScore object
            heartScore score = timestampSnapshot.getValue(heartScore.class);
            
            // If you want to keep the timestamp, assign the node's key to your object
            if (score != null) {
                score.setTimestamp(timestampSnapshot.getKey());
                userQuizEntries.add(score);
            }
        }
        
        // Now you have a list of all heartScore objects for the user
        // Use this list as needed (display, process, etc.)
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        // Handle errors (log, show user message, etc.)
        Log.e("FirebaseData", "Failed to fetch quiz entries", databaseError.toException());
    }
});

Android (Kotlin) #

Similar to Java, ensure your heartScore class has a no-arg constructor (or use data class with default values) and matches the database key names.

val userQuizRef = FirebaseDatabase.getInstance()
    .getReference("users")
    .child("-EvcKZHBZ4CVo9yAdlP7ldadCZS03")

userQuizRef.addValueEventListener(object : ValueEventListener {
    override fun onDataChange(dataSnapshot: DataSnapshot) {
        val userQuizEntries = mutableListOf<heartScore>()
        
        dataSnapshot.children.forEach { timestampSnapshot ->
            val score = timestampSnapshot.getValue(heartScore::class.java)
            score?.let {
                it.timestamp = timestampSnapshot.key
                userQuizEntries.add(it)
            }
        }
        
        // Process the list of heartScore objects
    }

    override fun onCancelled(databaseError: DatabaseError) {
        Log.e("FirebaseData", "Failed to fetch quiz entries", databaseError.toException())
    }
})

iOS (Swift) #

For Swift, make sure your heartScore struct/class conforms to Codable (Firebase supports Codable out of the box). Add an optional timestamp property if you want to store the entry's timestamp key.

import FirebaseDatabase

struct heartScore: Codable {
    var age: String
    var exercise_total: String
    // Add all other matching properties here
    var timestamp: String? // Optional, to store the timestamp key
}

// Fetch the user's quiz entries
let userQuizRef = Database.database().reference()
    .child("users")
    .child("-EvcKZHBZ4CVo9yAdlP7ldadCZS03")

userQuizRef.observe(.value) { snapshot in
    var userQuizEntries = [heartScore]()
    
    for child in snapshot.children {
        guard let timestampSnapshot = child as? DataSnapshot else { continue }
        
        // Map the snapshot data to heartScore
        do {
            var score = try timestampSnapshot.data(as: heartScore.self)
            score.timestamp = timestampSnapshot.key
            userQuizEntries.append(score)
        } catch {
            print("Failed to map entry: \(error.localizedDescription)")
        }
    }
    
    // Use the userQuizEntries list as needed
} withCancel: { error in
    print("Failed to fetch data: \(error.localizedDescription)")
}

Key Notes #

• Field Matching: Ensure your heartScore properties exactly match the database keys (case-sensitive!). If you prefer different naming in code, use annotations (Java/Kotlin) or CodingKeys (Swift) to map them.
• Data Types: Keep the data types consistent between your database and heartScore class. For example, if the database stores age as a string ("20"), your heartScore should have a String property for age (or convert it manually after mapping).
• One-Time vs Real-Time: Use addValueEventListener for real-time updates, or get() (Java/Kotlin) / getData() (Swift) if you only need to fetch the data once.

内容的提问来源于stack exchange，提问作者jlevis73