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lazy_columns

lazy_columns is a Rails plugin that lets you specify columns to be loaded lazily in your Active Record models.

By default, Active Records loads all the columns in each model instance. This plugin lets you specify columns to be excluded by default. It is intended for scenarios where you have large attributes and don't want to load them in every operation because of performance.

Notice that a much better approach is moving those columns to new models, since Rails loads related models lazily by default. This plugin is an easy workaround.

Installation

In your Gemfile

gem 'lazy_columns'

Usage

Use lazy_load in your Active Record models to define which column or columns should be loaded lazily:

class Action < ActiveRecord::Base
  lazy_load :comments

  attr_accessible :comments, :title
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" 

How the plugin works

This plugin does two things:

• Modify the default scope of the model so that it fetches all the attributes except the marked as lazy.
• Define an accessor method per lazy attribute that will reload the corresponding column under demand.

Eager loading of attributes defined as lazy

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 .select() in the initial query. For example:

Action.select(:comments).all 

Credits

• I learned about the possibility of using a default scope to exclude columns in this answer by Chris Hoffman in stackoverflow.