Question

我有以下课程：

class Car < ActiveRecord::Base

  has_many  :adverts, :dependent => :destroy
  has_many  :active_adverts, :class_name => 'Advert', :select => "adverts.id, adverts.availability_state, adverts.source_name, adverts.last_observed_at", :conditions => "availability_state = 'active'"

end

当我这样做：cars = Car.where(:brand => 'BMW').includes(:adverts)它工作正常，并返回我请求的汽车数组，广告正在急切加载。

如果我这样做：cars = Car.where(:brand => 'BMW').includes(:active_adverts)它似乎执行了预期的查询，但它返回了一个ActiveRecord::Relation对象，如果我问cars.first我得到：

NoMethodError: undefined method `each' for nil:NilClass
from /Users/nk/.rvm/gems/ruby-1.9.3-p194@au/gems/activerecord-3.2.13/lib/active_record/associations/preloader/association.rb:88:in `block in associated_records_by_owner'

我做错了什么？

PS。我按照她的建议：http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

它声明：

如果您确实希望只加载一个关联的某些成员通常更自然地包括具有条件的关联在其上定义：
class Post < ActiveRecord::Base
  has_many :approved_comments, :class_name => 'Comment', :conditions => ['approved = ?', true]
end
Post.includes（：approved_comments）这将加载帖子和急切加载 approved_comments关联，仅包含这些注释已被批准。

Answer 1

找到它，忘了在选择中选择外键car_id。

渴望加载条件关联

1 个答案: