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