我有一个Page包含许多Section模型的模型，这些模型与SectionRevisionthrough相关联current_revision。从Page模型中，我试图选择所有不为零Sections的地方。current_revision.parent_section_id
Section模型：
class Section < ActiveRecord::Base
belongs_to :page
has_many :revisions, :class_name => 'SectionRevision', :foreign_key => 'section_id'
has_many :references
has_many :revisions, :class_name => 'SectionRevision',
:foreign_key => 'section_id'
belongs_to :current_revision, :class_name => 'SectionRevision', :foreign_key => 'current_revision_id'
delegate :position, to: :current_revision
def set_current_revision
self.current_revision = self.revisions.order('created_at DESC').first
end
def children
Section.includes(:current_revision).where(:section_revisions => {:parent_section_id => self.id})
end
end
和Page型号：
class Page < ActiveRecord::Base
belongs_to :parent, :class_name => 'Page', :foreign_key => 'parent_page_id'
has_many :children, :class_name => 'Page', :foreign_key => 'parent_page_id'
belongs_to :page_image, :class_name => 'Image', :foreign_key => 'page_image_id'
has_many :sections
validates_uniqueness_of :title, :case_sensitive => false
def top_level_sections
self.sections.includes(:current_revision).where(:section_revisions => {:parent_section_id => "IS NOT NULL"})
end
end
Page.top_level_sections编写基于：Rails where condition using NOT NULL并且当前产生一个空数组。它不能正确检测“parent_section_id”是否不为空。
如何Page.top_level_sections正确书写？