JSON tree structure in Firebase - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Understanding Firebase JSON Tree Structure Output

Given the Firebase Realtime Database JSON tree below, what is the value returned when querying the path /users/user1/age?

Firebase

{
  "users": {
    "user1": {
      "name": "Alice",
      "age": 30,
      "active": true
    },
    "user2": {
      "name": "Bob",
      "age": 25,
      "active": false
    }
  }
}

A "Alice"

B true

C 30

D null

💡 Hint

Look at the path and find the value stored under 'age' for 'user1'.

The path /users/user1/age points to the number 30 in the JSON tree.

❓ Architecture

intermediate

Firebase JSON Tree Structure and Data Nesting

Which of the following JSON structures best represents a Firebase Realtime Database tree optimized to avoid deeply nested data for storing blog posts and their comments?

A

{
  "posts": {
    "post1": {
      "title": "Hello"
    }
  },
  "comments": {
    "post1": {
      "comment1": "Nice post!",
      "comment2": "Thanks for sharing"
    }
  }
}

B

{
  "posts": {
    "post1": {
      "title": "Hello",
      "comments": [
        "Nice post!",
        "Thanks for sharing"
      ]
    }
  }
}

C

{
  "posts": {
    "post1": {
      "title": "Hello",
      "comments": {
        "comment1": "Nice post!",
        "comment2": "Thanks for sharing"
      }
    }
  }
}

D

{
  "posts": {
    "post1": {
      "title": "Hello",
      "comments": "Nice post!"
    }
  }
}

💡 Hint

Firebase recommends flattening data to avoid deep nesting.

Option A separates posts and comments into different top-level nodes, avoiding deep nesting and improving scalability.

❓ security

advanced

Firebase JSON Tree Security Rules Impact

Given the Firebase Realtime Database JSON tree below, which security rule will allow only authenticated users to read their own profile data under /users/{userId} but deny access to others?

Firebase

{
  "users": {
    "user1": {"name": "Alice"},
    "user2": {"name": "Bob"}
  }
}

A

{
  "rules": {
    "users": {
      "$userId": {
        ".read": "auth != null",
        ".write": "auth != null"
      }
    }
  }
}

B

{
  "rules": {
    "users": {
      "$userId": {
        ".read": "auth != null && auth.uid == $userId",
        ".write": "auth != null && auth.uid == $userId"
      }
    }
  }
}

C

{
  "rules": {
    "users": {
      ".read": "auth != null",
      ".write": "auth != null"
    }
  }
}

D

{
  "rules": {
    "users": {
      "$userId": {
        ".read": "true",
        ".write": "auth != null && auth.uid == $userId"
      }
    }
  }
}

💡 Hint

Check the condition that matches the authenticated user's ID to the data path.

Option B restricts read and write access to only the authenticated user matching the userId in the path.

❓ Configuration

advanced

Firebase JSON Tree Update Behavior

If you perform an update operation on the Firebase Realtime Database path /users/user1 with the JSON {"age": 31}, what will be the resulting JSON subtree under /users/user1 given the initial data below?

Firebase

{
  "users": {
    "user1": {
      "name": "Alice",
      "age": 30,
      "active": true
    }
  }
}

A

{
  "name": "Alice",
  "age": 31,
  "active": true
}

B

{
  "age": 31
}

C

{
  "name": "Alice",
  "age": 30,
  "active": true
}

D

{
  "name": "Alice",
  "active": true
}

💡 Hint

Firebase update merges keys, it does not replace the entire node.

The update changes only the 'age' field to 31, keeping other fields intact.

🧠 Conceptual

expert

Analyzing Firebase JSON Tree Data Consistency

Consider a Firebase Realtime Database JSON tree where user profiles and their posts are stored separately as below. If a user deletes their profile, what is the best approach to ensure no orphan posts remain in the database?

Firebase

{
  "users": {
    "user1": {"name": "Alice"}
  },
  "posts": {
    "post1": {"author": "user1", "content": "Hello"},
    "post2": {"author": "user1", "content": "World"}
  }
}

A No action needed; orphan posts do not affect database consistency.

B Manually delete posts before deleting the user profile to avoid orphan posts.

C Rely on Firebase Realtime Database rules to automatically delete posts when user is deleted.

D Use Firebase Cloud Functions to trigger on user deletion and remove all posts with matching author ID.

💡 Hint

Think about automating cleanup to maintain data integrity.

Cloud Functions can listen to user deletions and clean up related posts automatically, ensuring no orphan data.