orderBy method
Implementation
List<Map<String, dynamic>> orderBy(String field, {bool descending = false}) {
final sortedDocuments = collection.values.toList()
..sort((a, b) => a[field].compareTo(b[field]));
return List<Map<String, dynamic>>.from(descending
? sortedDocuments.reversed.toList()
: sortedDocuments.toList());
}