Question

class student < ActiveRecord::Base
  has_many :projects

  def has_a_teacher_by_the_name_of(name)
    self.projects.any? { |project| project.teacher.exists?(:name => name) }
  end

end

class project < ActiveRecord::Base
  belongs_to :student
  has_one :teacher
end

class teacher < ActiveRecord::Base
  belongs_to :project
end

这不起作用，因为项目可能还没有教师，所以project.teacher会抛出错误：

当你没想到它时，你有一个零对象！评估nil.exists时发生错误？

Answer 1

您可以添加has_many :teachers, :through => :projects或将命名范围添加到Project：

class student < ActiveRecord::Base
  has_many :projects

  def has_a_teacher_by_the_name_of(name)
    self.projects.with_teacher.any? { |project| project.teacher.exists?(:name => name) }
  end

end

class project < ActiveRecord::Base
  belongs_to :student
  has_one :teacher
  scope :with_teacher, :conditions => 'teacher_id IS NOT NULL'
end

我该如何解决这个3模型的activerecord问题？

1 个答案: