Firebase: combine query and child event listener - firebase

Question

I have a structure similar to this
{
posts : {
post1Key: {
title : "First Post",
comments : {
comment1Key : {},
comment2Key : {},
comment3Key : {}
}
}
}
...
}
And I'm using the "child updated" events on the key "/posts/post1Key/comments" to listen for new comments.
How can I combine Firebase Query and the event listeners.
Edit: I know this is possible with Firebase, however, I'm using nativescript-plugin-firebase

Answer 1

You can very well combine a Query defined with an orderBy... method and a listener with the on() method: see detailed doc here
For example you could do something like
var query = db.ref('node1').orderByChild('firstName');
query.on('value', function(dataSnapshot) {
dataSnapshot.forEach(function(childSnapshot) {
var childKey = childSnapshot.key;
console.log(childKey);
var childData = childSnapshot.val();
console.log(childData);
});
});
Each time a new sub node is added under "node1" you will get the children list ordered by firstName

Answer 2

As at the time of writing, this isn't possible using the nativescript-plugin-firebase. The workaround is to do the sorting/filtering in the eventHandler after you have received the data.
var onChildEvent = function(result) {
//
// Sort: result.value here
//
};
// listen to changes in the /users path
firebase.addChildEventListener(onChildEvent, "/users").then(
function(listenerWrapper) {
var path = listenerWrapper.path;
var listeners = listenerWrapper.listeners; // an Array of listeners added
// you can store the wrapper somewhere to later call 'removeEventListeners'
}
);