尝试将Rails 5.0.7升级至5.2失败：Bundler未更新版本

Hey there, I’ve been in your exact spot before—trying to bump Rails versions and having Bundler refuse to budge. Let’s break down why this is happening and fix it step by step:

1. Fix Your Gemfile’s Rails Version Constraint #

The most common culprit is a strict version lock in your Gemfile. If it looks like either of these:

gem 'rails', '5.0.7' # Exact version lock
gem 'rails', '~> 5.0' # Only allows patch updates within 5.0.x

Bundler will never upgrade to 5.2. You need to loosen the constraint to target the 5.2 series:

gem 'rails', '~> 5.2' # Allows any 5.2.x patch release
# Or specify the latest 5.2 patch version directly:
gem 'rails', '5.2.8.1'

2. Clear Bundler’s Cache & Force a Fresh Update #

Sometimes old cached gems or locked dependencies get in the way. Run these commands in order:

• First, clean out cached gems: bundle clean --force
• Then, update Rails specifically: bundle update rails

If you still see the same message, check the output closely—Bundler will often hint at dependency conflicts that are blocking the upgrade.

3. Resolve Dependency Conflicts #

Other gems in your project might be tied to older Rails versions. For example, a gem that explicitly requires Rails 5.1 or lower will prevent Bundler from upgrading to 5.2. To find these conflicts:

• Run bundle update rails and read the error messages carefully (they’ll name the problematic gems)
• Use bundle outdated to see which gems have newer versions that support Rails 5.2
• For each conflicting gem, update its version in your Gemfile to a Rails 5.2-compatible release, then re-run bundle update

4. Reset Your Gemfile.lock (Last Resort) #

If your lock file is holding onto old constraints stubbornly, you can try resetting it:

1. Make a backup of Gemfile.lock (just in case something breaks)
2. Delete the original Gemfile.lock
3. Run bundle install to let Bundler re-resolve all dependencies from scratch using your updated Gemfile

Note: This will update all your gems to their latest compatible versions, so test thoroughly afterward.

5. Run rails app:update Correctly #

Remember: rails app:update only updates your app’s configuration files and generators—it doesn’t install the new Rails version. You need to get Bundler to install Rails 5.2 first (using the steps above), then run rails app:update to sync your app with the new version’s defaults.

Give these steps a shot, and if you run into specific dependency errors, feel free to share them and I’ll help you work through them!

内容的提问来源于stack exchange，提问作者Rahul