I am trying to determine if my transaction pattern is correct in my Cloud Function. As I understand, you should limit updates to child nodes. So I've tried to follow that general rule.
/functions/index.js
//not rate limited
//writes:
// - board.posts+1
// - thread.replies+1
// - thread.pages+1 if page count should change Math.ceil(thread.replies+1/POSTS_PER_PAGE)=pages
exports.newPost2 = require('./lib/new-post-2')(functions,firebase,rootRef,POSTS_PER_PAGE);
/functions/lib/new-post-2.js
module.exports = function(functions,firebase,rootRef,POSTS_PER_PAGE){
return functions.database.ref('/posts/{forum}/{board}/{thread}/{post}').onWrite(function(event){
// Only edit data when it is first created.
if (event.data.previous.exists()) {
return;
}
// Exit when the data is deleted.
if (!event.data.exists()) {
return;
}
var params = event.params;
var forum = params.forum;
var board = params.board;
var thread = params.thread;
var post = params.post;
//first increment the replies node of the thread.
rootRef.child('threads').child(forum).child(board).child(thread).child('replies').transaction(function(data) {
return data + 1;//increment reply count for thread.
}).then(function(snapshot){
//now, our snapshot should contain the updated value of replies.
var replies = snapshot.val();
//update the page count of the thread
rootRef.child('threads').child(forum).child(board).child(thread).child('pages').transaction(function(data) {
return Math.ceil(replies+1/POSTS_PER_PAGE);//replies is always +1 because OP of thread doesnt count as a reply.
});
//update the posts count for the board. this field is also updated by another firebase cloud function, when a thread is created
rootRef.child('forums').child(forum).child('boards').child(board).child('posts').transaction(function(data){
return data + 1;//increment post count for the board.
});
});
});
};
I'm worried about possibly racing while updating page count of thread and post count of board after the initial reply field is incremented on thread. I'm wondering if there is a safer way I can restructure this to update all 3 fields within the first transaction, if its possible.
