Rails Anti-Patterns

A guide to recognizing and fixing common anti-patterns in Rails applications. Each reference file shows what to avoid (Bad), explains why it's problematic, and demonstrates the correct approach (Good).

Controller Anti-Patterns

Business logic in controllers, non-RESTful route proliferation, and synchronous external calls in the request cycle.

• Fat Controller — Extract business logic to service objects (see service-patterns skill).
• Non-RESTful Custom Actions — Model state changes as nested RESTful resources instead of adding custom member actions.
• Blocking External Calls — Move external API calls to background jobs to keep requests fast and resilient.

For detailed Bad/Good examples, see references/controller-antipatterns.md.

Model Anti-Patterns

God objects, callback-driven side effects, invisible query scoping, and misused concerns.

• God Object — Extract focused modules, service objects, and query objects instead of accumulating unrelated responsibilities.
• Callback Hell — Reserve callbacks for data integrity operations intrinsic to the model. Orchestrate side effects in service objects.
• default_scope Abuse — Use explicit named scopes instead of default_scope, which applies silently to every query.
• Concerns as Junk Drawers — Keep concerns small, cohesive, and reusable. Splitting a god object across files does not fix the design.

For detailed Bad/Good examples, see references/model-antipatterns.md.

Query & Association Anti-Patterns

Tight coupling through deep object graphs, inefficient Ruby-side processing, and N+1 queries.

• Law of Demeter Violations — Use delegate instead of reaching deep into object graphs.
• Processing in Ruby Where SQL Suffices — Let the database filter, sort, and aggregate. See active-record-patterns skill.
• Missing Eager Loading (N+1) — Use includes, preload, or eager_load. See rails-performance skill.

For detailed Bad/Good examples, see references/query-antipatterns.md.

View & Hotwire Anti-Patterns

Logic-heavy templates, hidden partial dependencies, nil gymnastics, and misuse of Turbo/Stimulus. See hotwire-patterns skill for correct Hotwire patterns.

• Logic-Heavy Views — Extract conditional logic to helpers, presenters, or model methods.
• Instance Variables in Partials — Use strict locals (Rails 7.1+) to make dependencies explicit.
• Nil Gymnastics — Use the Null Object pattern or handle nil at the data layer.
• Turbo Streams When Frames Suffice — Use Turbo Frames for simple in-place updates.
• Stimulus for Everything — Let the server render HTML; use Turbo to deliver it.
• Ignoring Turbo Drive Compatibility — Use Stimulus controllers instead of DOMContentLoaded listeners.

For detailed Bad/Good examples, see references/view-antipatterns.md.

Background Job Anti-Patterns

Non-idempotent jobs, race conditions from enqueueing inside transactions, and serialization issues.

• Non-Idempotent Jobs — Add guard clauses and idempotency keys. Jobs will be retried.
• Enqueueing Inside Transactions — Enqueue after the transaction commits, or use after_commit.
• Complex Objects as Job Arguments — Pass only primitive IDs and let the job load fresh data.

For detailed Bad/Good examples, see references/job-antipatterns.md.

Migration Anti-Patterns

Fragile migrations that mix concerns or depend on application code.

• Mixing Schema and Data Migrations — Separate structural changes from data backfills into distinct migrations.
• Referencing Models in Migrations — Use raw SQL or inline model stubs instead of application model classes.

For detailed Bad/Good examples, see references/migration-antipatterns.md.

Quick Reference

Anti-Pattern	Fix
Fat controller	Extract to service object
Non-RESTful actions	Model as nested resources
Blocking external calls	Move to background jobs
God object	Extract concerns, services, and query objects
Callback hell	Use service objects for orchestration
default_scope	Use explicit named scopes
Concerns as junk drawers	Keep concerns small and cohesive
Law of Demeter violations	Use delegate
Ruby where SQL suffices	Use ActiveRecord query methods
N+1 queries	Use includes, preload, or eager_load
Logic-heavy views	Extract to helpers or presenters
Instance vars in partials	Use strict locals
Nil gymnastics	Null Object pattern
Streams when Frames suffice	Use Turbo Frames for in-place updates
Stimulus for everything	Let Turbo Drive and Frames handle navigation
DOMContentLoaded listeners	Use Stimulus controllers
Non-idempotent jobs	Add guard clauses and idempotency keys
Enqueueing inside transactions	Enqueue after commit
Complex objects as job args	Pass primitive IDs only
Mixed schema/data migrations	Separate into distinct migrations
Model classes in migrations	Use raw SQL or inline stubs

Additional Resources

Reference Files

For detailed Bad/Good code examples organized by category:

• references/controller-antipatterns.md — Fat controllers, non-RESTful actions, blocking calls
• references/model-antipatterns.md — God objects, callbacks, default_scope, concerns
• references/query-antipatterns.md — Law of Demeter, Ruby vs SQL, N+1 queries
• references/view-antipatterns.md — Logic-heavy views, partials, nil handling, Hotwire misuse
• references/job-antipatterns.md — Idempotency, transaction timing, serialization
• references/migration-antipatterns.md — Schema/data mixing, model references

Related Skills

• service-patterns — Service object, form object, and interactor patterns
• hotwire-patterns — Correct Turbo Frames, Turbo Streams, and Stimulus patterns
• active-record-patterns — Query and association patterns
• rails-performance — Eager loading and optimization strategies