ActiverecordLazyColumns

activerecord_lazy_columns is a gem that lets you specify columns to be loaded lazily in your Active Record models.

By default, Active Record loads all the columns in each model instance. This gem lets you specify columns to be excluded by default. This is useful to reduce the memory taken by Active Record when loading records that have large columns if those particular columns are actually not required most of the time. In this situation it can also greatly reduce the database query time because loading large BLOB/TEXT columns generally means seeking other database pages since they are not stored wholly in the record's page itself.

Notice that a better approach can be moving those columns to new models, since Active Record loads related models lazily by default. This gem is an easy workaround.

• ruby 3.2+
• activerecord 7.2+

Add this line to your application's Gemfile:

gem "activerecord_lazy_columns"

Use lazy_columns in your Active Record models to define which columns should be loaded lazily:

class Action < ApplicationRecord
  lazy_columns :comments
end

Now, when you fetch some action, the comments are not loaded:

Action.create!(title: "Some action", comments: "Some comments") # => <Action id: 1...>
action = Action.find(1) # => <Action id: 1, title: "Some action">

And if you try to read the comments attribute, it will be loaded into the model:

action.comments # => "Some comments"
action # => <Action id: 1, title: "Some action", comments: "Some comments"

This gem does two things:

• Modifies the default_scope of the model so that it fetches all the attributes except the ones marked as lazy.
• Defines a reader method per lazy attribute that will load the corresponding column under demand.

The first time you access a lazy attribute, a new database query will be executed to load it. If you are going to operate on a number of objects and want to have the lazy attributes eagerly loaded, use Active Record's .select() in the initial query. For example:

Action.select(:comments)

Thanks to the lazy_columns gem for the original idea.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/fatkodima/activerecord_lazy_columns.

The gem is available as open source under the terms of the MIT License.