Presenters

What it is

A Presenter (sometimes called a Decorator or View Object) wraps a model and adds display-only logic: formatted strings, conditional CSS classes, labels for enum values, HTML-safe output. It lives in the view layer and keeps the model clean.

Presenters are a better home for display logic than:

• Fat view helpers (hard to discover, no OO)
• Model methods like formatted_created_at (models shouldn't know about display)
• ERB conditionals repeated across multiple views

Would a fat model / helper do?

Use a helper if the formatting is generic and reused across many different models (e.g. time_ago_in_words). Keep it on the model if it's about domain state, not display. Extract a presenter when:

• A model has 3+ display-only methods (formatted dates, label strings, CSS classes)
• The same model is displayed differently in different contexts (list vs. detail view)
• Your helper module for one model is growing past 20 lines