When building real-world Rails apps, it’s common to hit the limits of traditional service objects. Here’s a practical breakdown of what you need to know — and what to do instead — based on our recent conversation.

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❓ Should I use .new or .for for services?

Use .for(config) when your service needs to select a subclass (e.g., inbound vs. outbound logic).

✅ Why .for is better here:

• It acts as a factory, returning the correct subclass.
• Avoids messy branching in controllers or the initializer.
• Keeps your API consistent (.fetch_and_persist_calls stays the same).
• Used in Rails itself (ActiveStorage::Service.for) and by trusted teams (like Thoughtbot).

Example: Nlpearl::ApiService.for(config) → returns InboundService or OutboundService based on direction.

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❓ What does “Instance Methods and Associations” mean?

Instead of putting logic in a service object, you can:

• Add instance methods directly to your model
• Use ActiveRecord associations to access related data
• Encapsulate logic where it belongs (next to the data)

✅ Benefit: Calling order.checkout is more natural than CheckoutService.new(order).call.

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❓ What if my model becomes too fat?

According to this article, when a model gets too bloated:

👇 Do this instead of writing service objects:

• ✅ Extract behavior into Concerns
• ✅ Use POROs (Plain Old Ruby Objects)
• ✅ Add meaningful instance methods
• ✅ Rely on ActiveRecord associations to reduce logic complexity
• 🚫 Avoid cramming everything into .call service objects unless absolutely needed

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❓ Aren’t POROs and service objects the same?

No — but they overlap.

• PORO = Any plain Ruby class (e.g., Money, Coordinate, MessageParser)
• Service object = A PORO used for a specific process (e.g., CreateBooking, SyncTickets)
• Not all POROs are service objects, but all service objects are POROs.

✅ Tip: Don’t overuse .call. Break logic into small POROs or model methods where possible.

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✅ Summary

Situation	Best Practice
Selecting between inbound/outbound	Use .for(config) factory method
Adding call logic	Use model_instance.checkout instead of service
Fat models	Extract to Concerns or POROs
Business process	Small, focused service object (only if needed)
General reusable logic	Use POROs (not necessarily service objects)