Dynamic `named_scope` depending on certain criterias

dear all, i have a Student model that i've specified some name_scope in it, e.g. from_program, from_year, from_school, has_status, from_course, etc...

i开发者_如何学JAVAs there anyway that i can chain the different named_scope together dynamically depending on certain criterias during runtime?

for example, if the user accessing the data is from Finance, i want to be able to chain from_school and has_status together only. if the user is the lecturer, i want to be able to chain from_course, from_school together, and so on...

should i use named_scope? or should i just fall back to the good old way of specifying conditions?

thanks for your suggestions in advance! =) btw i'm using rails 2.3

I'm not sure, if I understood, but I think you could do something like this:

class Student

  named_scope from_program, lambda{|program| :conditions => {:program => program}}
  named_scope from_year, lambda{|year| :conditions => {:year => year}}
  named_scope has_status, lambda{|status| :conditions => {:status => status}}

  def self.from_finance(school, status)
    self.from_school(school).has_status(status)
  end

end

or more general

def self.get_students(params)
  scope = self
  [:program, :year, :school, :course].each do |s|
    scope = scope.send("from_#{s}", params[s]) if params[s].present?
  end
  scope = scope.has_status(params[:status]) if params[:status].present?
  scope
end

You can try something like this

  Class User extend ActiveRecord::Base
  belongs_to :semester

  named_scope :year, lambda { |*year|
    if year.empty? || year.first.nil?
      { :joins => :semester, :conditions => ["year = #{CURRENT_SEMESTER}"]}
    else
      { :joins => :semester, :conditions => ["year = #{year}"]}
    end
    }

  end

You can call like this

  User.year     # defaults to CURRENT_SEMESTER constant
  User.year()  # same as above
  User.year(nil)  # same as above; useful if passing a param value that may or may not exist, ie, param[:year]
  User.year(2010)

In the same way you can pass parameters