push method
Generates a new child location using a unique key and returns a DatabaseReference to it. This is useful when the children of a Firebase Database location represent a list of items.
The unique key generated by childByAutoId: is prefixed with a client-generated timestamp so that the resulting list will be chronologically-sorted.
Implementation
DatabaseReference push() {
final String key = PushIdGenerator.generatePushChildName();
final List<String> childPath = List<String>.from(_pathComponents)..add(key);
return DatabaseReference._(_database, childPath);
}