rails-upgrade-3-to-4

To safely upgrade a legacy Rails 3 app to Rails 4, follow a phased upgrade path moving sequentially from 3.2 to 4.0, then 4.1, and finally 4.2. This hop sequence prevents skipping critical intermediate changes and avoids breaking API regressions.

The best way to migrate attr_accessible to strong parameters is using the protected_attributes_continued gem as a transitional bridge. This avoids risky all-at-once rewrites by providing a safe, phased transition from legacy mass-assignment protection to strong parameters.

Upgrading to Rails 4 can break existing jQuery event handlers due to Turbolinks integration. You must apply compatibility fixes for Turbolinks during the upgrade process to ensure custom event handlers and existing frontend functionality continue working correctly.

To migrate background workers when upgrading to Rails 4.2, you transition them to Active Job. This upgrade process involves overhauling the asset pipeline and auditing gem compatibility for common Rails 3-era dependencies to ensure seamless background job execution.

You should not skip intermediate versions when upgrading a Rails 3.2 application. A safe upgrade requires sequencing through 4.0 and 4.1 before reaching 4.2 to ensure no critical intermediate changes are skipped and deprecated patterns are handled correctly.