使用带有.includes down和up多个嵌套级别的.where IN子句在Rails 3.1中查找一组ID

Question

我想按学生班级筛选家长电子邮件地址列表。

以下是我的模型的简化：

Class District
 has_many :schools
 has_many :families
 has_many :children, :through => :families
 has_many :parents, :through => :families
 has_many :enrollments, :through => :children
end


Class Enrollments
 belongs_to :child
 belongs_to :classroom
end

电子邮件地址与家长记录相关联，我想按教室ID数组过滤电子邮件。

我可以让它工作：

idees = [49, 50]
current_district = District.first
@emails = current_district.parents.includes(:family => { :children => { :enrollments => {:classroom => { :program => :location }}}}).where("family_id IN (?)", idees)
# Returns families with ID 49 and 50

但我不能让这样的东西工作

idees = [49, 50]
current_district = District.first
@emails = current_district.parents.includes(:family => { :children => { :enrollments => {:classroom => { :program => :location }}}}).where("family.children.enrollments.classroom_id IN (?)", idees)
# Returns: PGError: ERROR:  cross-database references are not implemented: family.children.enrollment.classroom_id

我做错了什么?或者有没有另一种更好的方法来编写这个查询？

Answer 1

下面这行就是问题所在。

where("family.children.enrollments.classroom_id IN (?)", idees)

将其更改为：

where("enrollments.classroom_id IN (?)", idees)