Firebase：在单个事务中更新多个对象

Question

I have found some thread below which talk about this scenario.

• Firebase: How do I update multiple resources atomically
• Firebase data consistency across multiple nodes
• How to store users and groups for a chat using Firebase

However still struggling to find, if there are any recommended data structure design for this. I see a Multi-write library firebase-multi-write which says you probably don't need this in most cases.

But I think I do need this, my scenario is : 3 users

/users/A : {credit:20}

/users/B : {credit:3}

/users/C :  {credit:10}

And each user can steal credits from each other all at the same time .,

• A steals from B credits look like {21, 2}
• B steals from C credits look like {3, 9}
• C steals from A credits look like {11, 20}

Now I need to update the credits for each user to maintain this consistency, so that each steal operation is atomic in nature.

What will be the best way to handle such scenario, while maintaining data integrity in Java ?

Answer 1

In setember/2015 firebase developers released new version .

With this release, you can now do this in a single atomic update to both locations:

Firebase ref = new Firebase("https://<YOUR-FIREBASE-APP>.firebaseio.com");
// Generate a new push ID for the new post

Firebase newPostRef = ref.child("posts").push();
String newPostKey = newPostRef.getKey();

// Create the data we want to update
Map newPost = new HashMap();
newPost.put("title", "New Post");
newPost.put("content", "Here is my new post!");

Map updatedUserData = new HashMap();
updatedUserData.put("users/posts/" + newPostKey, true);
updatedUserData.put("posts/" + newPostKey, newPost);

// Do a deep-path update
ref.updateChildren(updatedUserData, new Firebase.CompletionListener() {
   @Override
   public void onComplete(FirebaseError firebaseError, Firebase firebase) {
       if (firebaseError != null) {
           System.out.println("Error updating data: " + firebaseError.getMessage());
       }
   }
});