Business or Domain Logic

Since business and domain logic is not required, nor encouraged, to go in your data models, where does it go?

It can go anywhere you like - Brut is not currently prescriptive.

Overview

It's recommended that you place classes in app/src/back_end. Any directory created in there will be auto-loaded by Brut/Zeitwerk based on its rules. This means that classes in any directory in app/src/back_end should not be namespaced.

For example, if you have commands and queries, you may want them in app/src/back_end/commands and app/src/back_end/queries, respectively. In this case, NewOrganizationCommand would go in app/src/back_end/commands/new_organization_command.rb and AccountQuery would go in app/src/back_end/queries/account_query.rb

Or, you could could organize them into app/src/back_end/business_logic/commands and app/src/back_end/business_logic/queries. In that case, Commands::NewOrganization would be expected in app/src/back_end/business_logic/commands/new_organization.rb and Queries::Account would be expected in app/src/back_end/business_logic/queries/account.rb.

How you organize it is up to you.

Testing

Tests can be written using RSpec in the usual way. Spec files should be in specs/back_end/path/to/class.spec.rb. Note that Brut expects Spec files to end in .spec.rb and not_spec.rb.

There is nothing special about the tests for your domain logic. Write them however you need to.

Recomended Practices

This could be an entire series of books. The main recommendation is to take a light approach and don't immediately install complex frameworks or libraries unless you know you need them.

Something somewhere in your business logic will need to interface with your front-end. The simplest way to do that is to allow form objects to be passed into your back-end. The second simplest way is to pass form values into your back-end.

You are strongly discouraged from having your front-end locate data models and pass those to your back-end. This can be done while prototyping and for fast iteration on a concept, but generally you do not want to query your database from your handlers or pages just to pass the results into a back-end class.

Exposing data models to the front-end is generally OK, as that is sometimes what you need to do.

Technical Notes

IMPORTANT

Technical Notes are for deeper understanding and debugging. While we will try to keep them up-to-date with changes to Brut's internals, the source code is always more correct.

Last Updated May 7, 2025

Creating universal abstractions from business logic is difficult. Brut is unlikely to do this. If it does, it will be after much analysis of exsiting patterns and only if it helps avoid mistakes and increases developer throughput.