Rails .where（）屬性不爲NULL

Question

我有一個Page模型，其中包含許多與SectionRevision到current_revision關聯的Section模型。從Page模型中，我試圖選擇所有Sections，其中current_revision.parent_section_id不是零。

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 

而且Page模型：

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基於寫成：Rails where condition using NOT NULL和目前生產空數組。它不能正確檢測「parent_section_id」是否爲空。

如何正確書寫Page.top_level_sections？

Answer 1

試試這個：

self.sections.includes(:current_revision). 
    where("section_revisions.parent_secti‌​on_id IS NOT NULL")