Method: ActiveRecord::QueryMethods#includes

Defined in:

lib/active_record/relation/query_methods.rb

#includes(*args) ⇒ Object

Specify relationships to be included in the result set. For example:

users = User.includes(:address)
users.each do |user|
  user.address.city
end

allows you to access the address attribute of the User model without firing an additional query. This will often result in a performance improvement over a simple join.

You can also specify multiple relationships, like this:

users = User.includes(:address, :friends)

Loading nested relationships is possible using a Hash:

users = User.includes(:address, friends: [:address, :followers])

conditions

If you want to add string conditions to your included models, you’ll have to explicitly reference them. For example:

User.includes(:posts).where('posts.name = ?', 'example')

Will throw an error, but this will work:

User.includes(:posts).where('posts.name = ?', 'example').references(:posts)

Note that #includes works with association names while #references needs the actual table name.

If you pass the conditions via hash, you don’t need to call #references explicitly, as #where references the tables for you. For example, this will work correctly:

User.includes(:posts).where(posts: { name: 'example' })

# File 'lib/active_record/relation/query_methods.rb', line 146

def includes(*args)
  check_if_method_has_arguments!(:includes, args)
  spawn.includes!(*args)
end