Fan-out writes pattern in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a fan-out update object for Firebase Realtime Database.

Firebase

const updates = {};
updates['/posts/' + postId] = postData;
updates[[1]] = postData;
return firebase.database().ref().update(updates);

Drag options to blanks, or click blank then click option'

A'/posts/' + userId + '/' + postId

B'/user-posts/' + userId + '/' + postId

C'/user-posts/' + postId

D'/posts/' + userId

Attempts:

3 left

💡 Hint

Common Mistakes

Using only postId without userId in the path.

Mixing up the order of userId and postId in the path.

In fan-out writes, you update multiple paths. Here, the second path is the user's posts path, which is '/user-posts/' + userId + '/' + postId.

2fill in blank

medium

Complete the code to perform a fan-out write using Firebase Admin SDK.

Firebase

const updates = {};
updates['/messages/' + messageId] = messageData;
updates[[1]] = messageData;
return admin.database().ref().update(updates);

Drag options to blanks, or click blank then click option'

A'/user-messages/' + messageId

B'/messages/' + userId + '/' + messageId

C'/user-messages/' + userId + '/' + messageId

D'/messages/' + userId

Attempts:

3 left

💡 Hint

Common Mistakes

Using only messageId without userId in the path.

Using the wrong base path for user messages.

The fan-out write updates both the general messages path and the user-specific messages path, which is '/user-messages/' + userId + '/' + messageId.

3fill in blank

hard

Fix the error in the fan-out write code to correctly update both paths.

Firebase

const updates = {};
updates['/comments/' + commentId] = commentData;
updates[[1]] = commentData;
return firebase.database().ref().update(updates);

Drag options to blanks, or click blank then click option'

A'/user-comments/' + commentId

B'/comments/' + commentId

C'/comments/' + userId + '/' + commentId

D'/user-comments/' + userId + '/' + commentId

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting userId in the user-specific path.

Using the wrong base path for user comments.

The correct fan-out path includes both userId and commentId to uniquely identify the comment under the user-comments path.

4fill in blank

hard

Fill both blanks to create a fan-out write that updates posts and user-posts paths.

Firebase

const updates = {};
updates[[1]] = postData;
updates[[2]] = postData;
return admin.database().ref().update(updates);

Drag options to blanks, or click blank then click option'

A'/posts/' + postId

B'/posts/' + userId + '/' + postId

C'/user-posts/' + userId + '/' + postId

D'/user-posts/' + postId

Attempts:

3 left

💡 Hint

Common Mistakes

Using userId in the general posts path.

Omitting userId in the user-posts path.

The first path is the general posts path '/posts/' + postId, and the second is the user-specific posts path '/user-posts/' + userId + '/' + postId.

5fill in blank

hard

Fill all three blanks to complete the fan-out write for messages, user-messages, and user-inbox paths.

Firebase

const updates = {};
updates[[1]] = messageData;
updates[[2]] = messageData;
updates[[3]] = true;
return firebase.database().ref().update(updates);

Drag options to blanks, or click blank then click option'

A'/messages/' + messageId

B'/user-messages/' + userId + '/' + messageId

C'/user-inbox/' + userId + '/' + messageId

D'/messages/' + userId + '/' + messageId

Attempts:

3 left

💡 Hint

Common Mistakes

Using userId in the general messages path.

Omitting userId in user-specific paths.

Using incorrect values for the inbox update.

The fan-out write updates the general messages path, the user-specific messages path, and marks the message as present in the user's inbox with a boolean true.