Discussion: make apps optional — Rails-style flat project structure

[papilip]

Context

Coming from a Rails background, the Marten app system feels restrictive for small to medium projects. In our production project (subscriptions, donations, e-commerce, admin dashboard), we ended up with:

• auth/ — logical, isolated domain
• abonnements/ — became a catch-all (subscriptions, donations, orders, cart, shop, signup)
• admin/ — back-office

The abonnements app grew organically and would benefit from being split, but adding more apps means more boilerplate (app.cr files, migration dependencies, template nesting).

Proposal: allow flat project structure without apps

Rails doesn't require apps — models, controllers, and views live directly in the project. Marten already has a MainConfig (label `main`) for the root `src/` directory. The remaining friction is:

1. Table name prefix

Currently, models in `src/` get `main_` prefix (`main_user`, `main_order`). For the main app, no prefix would be more natural:

```crystal

Current: main_user

Desired: user (or configurable)

```

Suggestion: `MainConfig` should default to an empty prefix. Or allow per-app prefix configuration:

```crystal
class App < Marten::App
label :my_app
db_table_prefix "" # no prefix
end
```

2. Migrations in src/migrations/

Models in `src/` should have their migrations in `src/migrations/` (already supported via `MainConfig`).

3. Templates in src/templates/

This already works — `src/templates/` is a default template directory.

Rails → Marten comparison

Rails	Marten (current)	Marten (proposed)
`app/models/user.rb`	`src/apps/auth/models/user.cr`	`src/models/user.cr`
`app/controllers/users_controller.rb`	`src/apps/auth/handlers/users_handler.cr`	`src/handlers/users_handler.cr`
`app/views/users/`	`src/apps/auth/templates/auth/`	`src/templates/users/`
`db/migrate/`	`src/apps/auth/migrations/`	`src/migrations/`
No app file needed	`src/apps/auth/app.cr` required	No app file needed

Impact

This would be a non-breaking change:

• Existing apps continue to work exactly as before
• The flat structure is opt-in for new/simple projects
• Complex projects can still use apps for isolation

Questions

• Should `MainConfig` default to no prefix?
• Should there be a CLI option: `marten new project --flat` vs `marten new project --apps`?
• How should `marten new app` behave in a flat project?

[ellmetha]

Hey! 👋

Thanks for the thoughtful proposal. I totally see where you’re coming from, especially with a Rails background.

That said, applications in Marten are a core design choice and not meant to be optional. The framework intentionally encourages splitting code into apps to enforce clear boundaries and avoid “catch-all” structures as projects grow (similar to Django).

While using only the main app is possible for very small projects, it’s more of a convenience than a recommended structure. Introducing a flat mode (no apps, no prefixes, etc.) would go against this philosophy and add complexity by supporting two different project organization modes.

More broadly, Marten is not meant to be a clone of Rails or to specifically accommodate Rails conventions. While it takes inspiration from frameworks like Ruby on Rails and Django, it ultimately follows its own principles and design decisions.