Modular code generation

By default, drift generates code from a single entrypoint - all tables, views and queries for a database are generated into a single part file. For larger projects, this file can become quite large, slowing down builds and the analyzer when it is re-generated. Drift supports an alternative and modular code-generation mode intended as an alternative for larger projects. With this setup, drift generates multiple files and automatically manages imports between them.

As a motivating example, consider a large drift project with many tables or views being split across different files:

lib/src/database/
├── database.dart
├── tables/
│   ├── users.drift
│   ├── settings.drift
│   ├── groups.drift
│   └── search.drift
└── views/
    ├── friends.drift
    └── categories.dart

While a modular structure (with imports in drift files) is helpful to structure sources, drift still generates everything into a single database.g.dart file. With a growing number of tables and queries, drift may need to generate tens of thousands of lines of code for data classes, companions and query results.

With its modular generation mode, drift instead generates sources for each input file, like this:

lib/src/database/
├── database.dart
├── database.drift.dart
├── tables/
│   ├── users.drift
│   ├── users.drift.dart
│   ├── settings.drift
│   ├── settings.drift.dart
│   └── ...
└── views/
    ├── friends.drift
    ├── friends.drift.dart
    ├── categories.dart
    └── categories.drift.dart

Enabling modular code generation

Note: A small example using modular code generation is also part of drift's repository.

As drift's modular code generation mode generates different file patterns than the default builder, it needs to be enabled explicitly. For this, create a build.yaml file in which you disable the default drift_dev build and enable the two builders for modular generation: drift_dev:analyzer and drift_dev:modular. They should both get the same options:

targets:
  $default:
    builders:
      drift_dev:
        # disable drift's default builder, we're using the modular setup
        # instead.
        enabled: false

      # Instead, enable drift_dev:analyzer and drift_dev:modular manually:
      drift_dev:analyzer:
        enabled: true
        options: &options
          # Drift build options, as per https://drift.simonbinder.eu/docs/advanced-features/builder_options/
          store_date_time_values_as_text: true
          named_parameters: true
          sql:
            dialect: sqlite
            options:
              version: "3.39"
              modules: [fts5]
      drift_dev:modular:
        enabled: true
        # We use yaml anchors to give the two builders the same options
        options: *options

What gets generated

With modular generation, drift generates standalone Dart libraries (Dart files without a part of statement). This also means that you no longer need part statements in your sources. Instead, you import the generated .drift.dart files. And of course, every private mixin/class previously generated under the part files will now be public. Replacing all _$ (notice the leading space) with $ (leading space here as well) should probably fix those problems there.

When it comes to using the generated code, not much is different: The API for the database and DAOs stays mostly the same. A big exception are how .drift files are handled in the modular generation mode. In the default builder, all queries in all drift files are generated as methods on the database. With modular code generation, drift generates an implicit database accessor reachable through getters from the database class. Consider a file user.drift like this:

CREATE TABLE users (
  id INTEGER NOT NULL,
  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
  name TEXT NOT NULL,
  is_admin BOOLEAN NOT NULL DEFAULT FALSE
);

findUsers($predicate = TRUE): SELECT * FROM users WHERE $predicate;

If such a users.drift file is included from a database, we no longer generate a findUsers method for the database itself. Instead, a users.drift.dart file contains a database accessor called UsersDrift which is implicitly added to the database. To call findUsers, you'd now call database.usersDrift.findUsers().