CODEWITHSUNDEEP
mysqlruby-on-rails
Hommer Smith
Hommer Smith

Reputation: 27852

When does Rails perform the query and loads into memory?

If I have a User table and House table and I do this:

users = User.where(status: 3)

homes = Home.joins(:user).merge(users)

On the first assignation am I performing a query already? Or it waits until the second to perform the query? Or it does it when you actually try to access any of those results? How does Rails manage to know when to perform the query?

Upvotes: 1

Views: 1642

Answers (1)

mr. Holiday
mr. Holiday

Reputation: 1800

The where method returns an ActiveRecord::Relation object, and by itself this object does not issue a database query. It's where you use this object that matters. join method as well lazy loads the database query by utilising the associated table, but only loading the Home table into memory as the associated User table is not required. Afterwards you have merge, what merge method does is a simple way of using a named scope on a joined model. Something like 

class Home < ActiveRecord::Base
  has_many :users
end

class User < ActiveRecord::Base
  belongs_to :home

  scope :available, ->{ where(available: true) }
end

Upvotes: 1

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