Add source to existing layer in mapbox GL - asynchronous

Question

The title pretty much says what I intend to do.
I am using Firebase as backend for markers on a map and use the on('child_added') method to monitor these. For every node on a specific location in the database, the on('child_added') will fire once.
This also applies to new nodes being created, hence this is perfect for asynchronously adding new markers to the map as they are added to the database.
In order display these on a map, mapbox GL requires me to transform the data to geojson, create a source and then add this source to a layer. The code below shows this and it actually displays the markers on the map.
markersRef.on('child_added', function(childSnapshot) { //fires once for every child node
var currentKey = childSnapshot.key; //the key of current child
var entry = childSnapshot.val(); //the value of current child
//creates a geojson object from child
var geojson = {
"type": "FeatureCollection",
"features": [{
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [entry.position.long, entry.position.lat]
}
}],
"properties": {
title: entry.title,
text: entry.text
}
};
//creates a source with the geojson object from above
map.addSource(currentKey, { //currentKey is the name of this source
"type": "geojson",
"data": geojson,
cluster: true //clusters the points in this source
});
//adds the source defined above to a layer that will be displayed on a map
map.addLayer({
"id": currentKey, // Sets id as current child's key
"source": currentKey, // The source layer defined above
});
});
The problem is that the markers will be in individual sources, making them appear on different layers. Therefore, I cannot cluster them or e.g. search across them.
What I look for is a way to add a source to an existing layer. This would enable me to create a layer outside the on('child_added') method and then add the sources to this layer.
I have looked at the mapbox GL docs but I cannot find anything in there that will enable me to do this. It seems very limited in this respect compared to mapbox js.
I see this as a pretty important feature and don't understand why this is not possible. I hope some of you have a workaround or a way to achieve asynchronously adding markers to a map in mapbox GL.

Answer 1

I have the same problem. I did some searching on this and I found the setData attribute for GeoJSONSource:
https://www.mapbox.com/mapbox-gl-js/api/#geojsonsource#setdata
map.addSource("points", markers);
map.addLayer({
"id": "points",
"type": "symbol",
"source": "points",
"layout": {
"icon-image": "{icon}-15",
"icon-allow-overlap": true,
"icon-ignore-placement": true,
"icon-size": 2,
"icon-offset": [0, -10],
}
});
Then later I update the source, without creating a new layer like so:
map.getSource('points').setData(newMarkers)
So this updates the source without creating a new layer. Then you can search over this layer. The only problem I encountered was that setData erases all the previous data (there is no "addData" functionality) so you need to save the previous markers and add them again. Let me know if you find a workaround for this.

Answer 2

As the documentation at https://www.mapbox.com/mapbox-gl-js/api/#geojsonsource states: A GeoJSON data object or a URL to one. The latter is preferable in the case of large GeoJSON files.
What happens here is that geojson sources loaded via a url are loaded using a background thread worker so they do not affect the main thread, basically always load your data via url or a mapbox style to offload all JSON parsing and layer loading to another thread. Thus anytime you have a change event fired from your firebase monitoring you can simply reload the url you are using to initially load the source.
In addition, the founder of Leaflet and amazing Mapbox Developer Vladimir Agafonkin discusses this here: https://github.com/mapbox/mapbox-gl-js/issues/2289, and it is essentially what they do in their real-time example: https://www.mapbox.com/mapbox-gl-js/example/live-geojson/.
Furthermore, here is an example with socket.io I use client side:
const url = {server url that retrieves geojson},
socket = {setup all your socket initiation, etc};
socket.on('msg', function(data) {
if (data) {
//Here is where you can manipulate the JSON object returned from the socket server
console.log("Message received is: %s", JSON.stringify(data));
if(data.fetch){
map.getSource('stuff').setData(url)
}
} else {
console.log("Message received is empty: so it is %s", JSON.stringify(data));
}
});
map.on('load', function(feature) {
map.addSource('events', {
type: 'stuff',
data: url
});
map.addLayer({
"id": "events",
"type": "symbol",
"source": "events",
"layout": {
"icon-image": "{icon}"
}
});
});