Hive: generate adapters for classes in multiple .dart files

I have classes defined in individual files. I want to store all of the classes in a single Hive box. I cannot see how to register the adapters for the separate files and have them generated into a single .part file. Do I need to create a method and explicitly call the method to register the adapters? I've tried registering them in the Main() method of main file, but that doesn't work. After running build_runner, the additional adapters are not in the .part file.

CLASS A

import 'package:hive/hive.dart';
import 'package:my_project/class_b.dart';
import 'package:my_project/class_c.dart';
...
@HiveType(typeId: 0)
class ClassA {
  @HiveField(0)
  String string ="";
...
void main(List<String> arguments) async {
 var path = "assets/";
  Hive
..registerAdapter(ClassAAdapter());
..registerAdapter(ClassBAdapter()); //???
...
}

CLASS B

import 'package:hive/hive.dart';
    ...
    @HiveType(typeId: 1)
    class ClassB {
      @HiveField(0)
      String string ="";
    ...
void initAdapters() { //???
     var path = "assets/";
      Hive  // ??????
    ..registerAdapter(ClassBAdapter()); //???
}