如何利用ruby procs动态执行数据库查询

Question

我有一个名为Bucket的模型，该模型具有此实例方法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

现在，此查询返回一组学生的学业成绩介于一系列值之间

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

我从像这样的bucket实例中调用此方法bucket.populate_students_academicwise(mentor)

我想否定该查询，也就是说，返回一组学习成绩不在一定范围内的学生。 我所能想到的就是创建另一个对上述查询运行否定的方法。 所以我有另一种方法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

现在，此查询返回一组学习成绩ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ?范围值ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ?之间的学生ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ? ROUND(AVG(marks_obtained)/AVG(marks_total)*100) NOT BETWEEN ? AND ?

我该如何调用第一个方法Bucket#populate_students_academicwise(mentor)并在其上附加一个否定方法bucket.populate_students_academicwise(mentor).negate ，该方法将调用proc来否定查询？

Answer 1

因此，您想基本上同时具有这两种功能，并且仍然以DRY方式拥有它们？

我会说您应该使用默认参数。

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

你内在的方法

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

通过少量的查询操作，您可以根据参数获得NOT（或没有NOT），而无需担心proc。