Run build_runner for existing sqlite database

Question

i am working on a flutter app which will have localDB for Native and Web. For that i am using drift - 2.16.0 dependency package.We can create database class and table structures then if we call the build_runner it will automatically generate the 'example.g.dart' file for us.How can we achieve the same for existing sqlite database.

database file added into project like below in pubspec.yaml

flutter:
  assets:
    - assets/example.db