如何利用ruby procs動態執行數據庫查詢

Question

我有一個名為Bucket的模型，該模型具有此實例方法Bucket#populate_students_academicwise(mentor)

def populate_students_academicwise(mentor)
  student_ids = Mark.find(:all,
    :joins => self.student_current_klass,
    :conditions => ["marks.subject_id = ? AND st.klass_id = ? AND marks.klass_id = ? AND u.account_enabled IS TRUE AND sub.active IS TRUE AND k.active IS TRUE", mentor.subject_id, mentor.klass_id, mentor.klass_id],
    :group => "marks.student_id",
    :having => ["ROUND(AVG(marks_obtained)/AVG(marks_total)*100) BETWEEN ?  AND  ?", min_range, max_range]).collect(&:student_id)

  self.assign_students(student_ids)
end

現在，此查詢返回一組學生的學業成績介於一系列值之間

ROUND(AVG(marks_obtained)/AVG(marks_total)*100) BETWEEN ?  AND  ?)

我從像這樣的bucket實例中調用此方法bucket.populate_students_academicwise(mentor)

我想否定該查詢，也就是說，返回一組學習成績不在一定范圍內的學生。 我所能想到的就是創建另一個對上述查詢運行否定的方法。 所以我有另一種方法Bucket#negate_populate_students_academicwise(mentor)

def negate_populate_students_academicwise(mentor)
    Mark.find(:all,
      :joins => self.student_current_klass,
      :conditions => ["marks.subject_id = ? AND st.klass_id = ? AND marks.klass_id = ? AND u.account_enabled IS TRUE AND sub.active IS TRUE AND k.active IS TRUE", mentor.subject_id, mentor.klass_id, mentor.klass_id],
      :group => "marks.student_id",
      :having => ["ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ?  AND  ?", min_range, max_range]).collect(&:student_id)
end

現在，此查詢返回一組學習成績ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ?范圍值ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ?之間的學生ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ? ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ?

我該如何調用第一個方法Bucket#populate_students_academicwise(mentor)並在其上附加一個否定方法bucket.populate_students_academicwise(mentor).negate ，該方法將調用proc來否定查詢？

Answer 1

因此，您想基本上同時具有這兩種功能，並且仍然以DRY方式擁有它們？

我會說您應該使用默認參數。

bucket.populate_students_academicwise(mentor) # dont negate
bucket.populate_students_academicwise(mentor,false) # negate

你內在的方法

def populate_students_academicwise(mentor,in_range = true)
  student_ids = Mark.find(:all,
                   :joins => self.student_current_klass,
                   :conditions => ["marks.subject_id = ? AND st.klass_id = ? AND marks.klass_id = ? AND u.account_enabled IS TRUE AND sub.active IS TRUE AND k.active IS TRUE", mentor.subject_id, mentor.klass_id, mentor.klass_id],
                   :group => "marks.student_id",
                   :having => ["ROUND(AVG(marks_obtained)/AVG(marks_total)*100) #{'NOT' if !in_range} BETWEEN ?  AND  ?", min_range, max_range]).collect(&:student_id)
  self.assign_students(student_ids)
end

通過少量的查詢操作，您可以根據參數獲得NOT（或沒有NOT），而無需擔心proc。