Ruby on Rails 6.1: What's New, Release History & Support Lifecycle

What Is New in Ruby on Rails 6.1

How does Rails 6.1 improve database connection handling and sharding?

Rails 6.1 introduces per-database connection switching and native horizontal sharding support.

• Set config.active_record.legacy_connection_handling = false to enable the new API.
• Use connected_to on an abstract class to switch only the desired database role.
• Horizontal sharding is now possible because a model can have separate connections per role.

class ReportingBase < ApplicationRecord
  self.abstract_class = true
  connects_to database: { writing: :primary, reading: :primary_replica }
end

ReportingBase.connected_to(role: :reading) do
  # All queries inside this block use the replica only
end

How can I prevent N+1 queries with the new strict loading feature?

Strict loading forces all associations to be eager-loaded, raising an error if a lazy load occurs.

• Enable globally with ActiveRecord::Base.strict_loading! or per-model with strict_loading!.
• When a lazy load is attempted, Rails raises ActiveRecord::StrictLoadingViolationError, letting you catch N+1 problems early.

# Enable strict loading for the whole app
ActiveRecord::Base.strict_loading!

user = User.first          # raises if any association is not preloaded

What options does Rails 6.1 give for model inheritance and background destruction?

Delegated types replace STI for concrete super-classes, and destroy associations can now be queued to a background job.

• Delegated types let the superclass have its own table while each subclass lives in a separate table.
• Use dependent: :destroy_async to offload heavy deletions to Active Job.

class Vehicle < ApplicationRecord
  delegated_type :vehicle_type, types: %w[Car Truck], dependent: :destroy
end

class Car < ApplicationRecord; end
class Truck < ApplicationRecord; end

class Post < ApplicationRecord
  has_many :comments, dependent: :destroy_async
end

What query behavior changes should I be aware of in Active Record 6.1?

Where.not now generates NAND predicates, and scope-leakage bugs have been fixed.

• where.not produces NOT (cond1 AND cond2) instead of separate != clauses.
• Creating records inside a scoped create block no longer leaks the scope to class-level queries.
• Named scopes no longer inherit the caller's scope, preventing accidental double-filtering.

User.where.not(name: "Jon", role: "admin")
# => SELECT ... WHERE NOT (name = 'Jon' AND role = 'admin')

What are the notable updates to Action View, Active Storage and Active Model errors?

Action View now requires a compiled method container, preload link headers can be disabled, Active Storage adds a new upload API, and Active Model errors are objects.

• ActionView subclasses must implement #compiled_method_container.
• Set config.action_view.preload_links_header = false to stop automatic Link headers.
• ActiveStorage introduces Blob.create_and_upload and a service_name column (run the migration generated by rails app:update).
• Model errors are now instances of ActiveModel::Errors with a queryable API.