Why Does Firebase Event Return Empty Object On Second And Subsequent Events?

I have a Python Firebase SDK on the server, which writes to Firebase real-time DB. I have a Javascript Firebase client on the browser, which registers itself as a listener for 'chi

Solution 1:

I found the answer. Like most things, it turned out to be simple, but took a couple of days to find. Maybe this will save someone else.

On the docs page: http://firebase.google.com/docs/database/admin/save-data#section-push

"In JavaScript and Python, the pattern of calling push() and then immediately calling set() is so common that the Firebase SDK lets you combine them by passing the data to be set directly to push() as follows..."

I suggest the wording should emphasize that you must do it that way.

The earlier Python example on the same page doesn't work:

new_post_ref = posts_ref.push()
new_post_ref.set({
    'author': 'gracehop',
    'title': 'Announcing COBOL, a New Programming Language'
})

A separate empty push() followed by set(data) as in this example, won't work for Python and Javascript because in those cases the push() implicitly also does a set() and so an empty push triggers unwanted event listeners with empty data, and the set(data) didn't trigger an event with data, either.

In other words, the code in the question:

new_post_ref = posts_ref.push()
new_post_ref.set(data)

must be:

new_post_ref = posts_ref.push(data)

with set() not explicitly called.

Since this push() code happens only when new objects are written to FB, the initial download to the client wasn't affected.

Though the documentation may be trying to convey the evolution of the design, it fails to point out that only the last Python and Javascript example given will work and the others shouldn't be used.