Rails 4 → 5 Upgrade

Rails 4.2 → 5.0 is one of the biggest API breaks in the past decade. params stop being a Hash. Strong parameters become mandatory. ApplicationRecord arrives. Treat as a multi-month project for a non-trivial app.

The opinion

Dual-boot with next_rails. Hop 4.2 → 5.0 → 5.1 → 5.2. Ruby 2.2.2+ required for the whole 5.0–5.2 series (Rails' own gemspec never raised the floor within Rails 5). Budget weeks-to-months for a non-trivial app.

The hop sequence

4.2 → 5.0 → 5.1 → 5.2

Core patterns

Pattern 1: 4.2 → 5.0 — the breaking changes

Required code changes: