Eager Load 间接关联 Rails

Question

关联如下：

#app/models/pet.rb
class Pet < ActiveRecord::Base
  belongs_to :pet_store
end

#app/models/pet_store.rb
class PetStore < ActiveRecord::Base
    has_many :pets, dependent: :destroy
    has_many :employees, dependent: :destroy
end

#app/models/employee.rb
class Employee < ActiveRecord::Base
  belongs_to :pet_store
end

我想做这样的事情，这会导致N + 1 错误：

@pets = Pet.where(species: "Dog").includes(:pet_store)
@pets.each do |pet|
  pet.pet_store.employees.each do |employee|
    puts employee.name
  end
end

这会导致 N+1 错误，因为必须对每个 employee 进行查询。我想eager load 间接关联employees。但是，我不能简单地includes(:employees)，因为pet 与employees 没有直接关联。如何做到这一点？

Answer 1

你可以：

@pets = Pet.includes(:pet_store => :employees)

Rails 查询语言指南很棒。这是docs on eager-loading。