Add Rails 8.1 compatibility improvements

[takaokouji]

Summary

This PR adds Rails 8.1 compatibility improvements while maintaining full backward compatibility with earlier Rails versions (6.1, 7.0, 7.1).

Based on the excellent work by @simps614 in upstream PR cerebris#1485.

Changes

1. CSV gem dependency

• File: Gemfile
• Change: Added csv gem for Rails 8.1+ (removed from standard library)
• Reason: Required by lib/jsonapi/acts_as_resource_controller.rb:3

2. HTTP status code compatibility

• Files: lib/jsonapi/exceptions.rb, test/controllers/controller_test.rb, test/test_helper.rb, test/helpers/functional_helpers.rb
• Change: Updated :unprocessable_entity to conditionally use :unprocessable_content for Rails 8.0+
• Reason: Avoid deprecation warnings in Rails 8.0+ while maintaining backward compatibility
• Implementation:
  • Added unprocessable_status helper method in JSONAPI::Exceptions::Error and test helpers
  • Updated test assertions to use the helper method
  • Uses :unprocessable_content when Rails::VERSION::MAJOR >= 8

3. Database adapter improvements

• File: test/unit/active_relation_resource_finder/join_manager_test.rb
• Change: Simplified db_true helper to use ActiveRecord::Base.connection.quoted_true
• Reason: More concise, database-agnostic approach

Backward Compatibility

All changes maintain full backward compatibility:

• Rails 6.1, 7.0, 7.1: Uses :unprocessable_entity (existing behavior)
• Rails 8.0, 8.1+: Uses :unprocessable_content (avoids deprecation warnings)

Testing

All tests pass with Rails 6.1, 7.0, 8.0, and 8.1:

# Rails 6.1
docker-compose run rails-6.1
# ✅ 704 runs, 8832 assertions, 0 failures, 0 errors, 0 skips

# Rails 7.0
docker-compose run rails-7.0
# ✅ 704 runs, 8832 assertions, 0 failures, 0 errors, 0 skips

# Rails 8.0
docker-compose run rails-8.0
# ✅ 704 runs, 8838 assertions, 0 failures, 0 errors, 0 skips
# ✅ No :unprocessable_entity deprecation warnings

# Rails 8.1
docker-compose run rails-8.1
# ✅ 704 runs, 8838 assertions, 0 failures, 0 errors, 0 skips
# ✅ No :unprocessable_entity deprecation warnings

Credits

Based on the work by @simps614 (Cassie Simpson) in cerebris#1485.

Related Issues

• Upstream PR: Rails 8_1 Compatibility cerebris/jsonapi-resources#1485
• Upstream Issue: Rails 8.1: jsonapi_resources DSL fails to generate relationship routes due to Resource#initialize signature change cerebris/jsonapi-resources#1479