rails-error-prevention_skill

Overview

This skill provides an expert checklist to prevent common Rails runtime errors before writing code. It focuses on ViewComponents, GROUP BY/Postgres grouping issues, method exposure between layers, N+1 detection, nil guards, and controller/template mistakes. Follow it as a pre-flight to catch mistakes early and avoid runtime debugging.

How this skill works

The skill inspects your planned change against a set of verification steps: check component templates and public methods, ensure helper usage is delegated, validate GROUP BY queries for non-aggregated columns, verify eager-loading patterns to avoid N+1, and confirm controller/view render expectations. It provides concrete shell and Ruby snippets to run in your project and a short checklist for each area to enforce before coding.

When to use it

• Creating or modifying a ViewComponent (ensure template & helpers)
• Writing ActiveRecord GROUP BY or aggregation queries
• Building views that call component methods or service methods
• Debugging undefined method / NoMethodError related to nil or exposure
• Investigating N+1 queries or ambiguous column errors
• Adding or changing controller actions and view templates

Best practices

• Always verify component template pattern (inline vs file) before creating a component
• List view calls and match them to public component methods before writing view code
• Prefix Rails helpers with helpers. inside ViewComponents or delegate them explicitly
• For GROUP BY: include every non-aggregated column in GROUP BY and avoid includes/preload with grouping
• Detect and fix N+1 by using includes/preload/eager_load appropriately and test in console
• Use safe navigation, guard clauses, and early returns to prevent nil-related NoMethodError

Example use cases

• Before adding a new dashboard component: confirm .rb and template exist, list required methods, add delegations or wrappers
• Before converting reports to grouped SQL: ensure selected columns are aggregated or grouped and remove includes from the grouped query
• When a view raises undefined method for component: run the grep checks to list missing methods and add them to the component
• When logs show repeated user queries: add includes(:user) or preload and re-run the console test
• Before adding a controller action: ensure a template exists or the action explicitly renders or redirects