% rake rails:freeze:edge

% rails edge_080518
% cd edge_080518/rails
% git clone git://github.com/rails/rails.git

rake time:zones:*

% ./script/generate model person name:string age:integer gender:integer
% rake db:migrate

>> Person.create :name => 'person 1', :age => 20, :gender => 1

    >> Person.create do |p|
    >>   p.name = 'person 2'
    >>   p.age = 30
    >>   p.gender = 2
    >> end

    >> Person.create :name => 'person 3', :age => 3, :gender => 1

class Person < ActiveRecord::Base
      # Hashで conditions。基本形。
      named_scope :male, :conditions => {:gender => 1}
      named_scope :female, :conditions => {:gender => 2}
      # Stringで conditions。
      named_scope :adult, :conditions => 'age >= 20'
      # Procで scopeを定義した形。例がへぼくてすいません。
      named_scope :name_start_with_p, lambda { {:conditions => ["name like ?", 'p%']} }
      # Proc方式だと scopeに引数も渡せる。
      named_scope :older_than, lambda {|n| {:conditions => ['age >= ?', n]} }
      # さっきのへぼい例もこれなら実用的。
      named_scope :name_start_with, lambda {|s| {:conditions => ["name like ?", "#{s}%"]} }
    end

>> Person.male
  Person Load (0.000603)   SELECT * FROM "people" WHERE ("people"."gender" = 1)
>> Person.adult
  Person Load (0.000596)   SELECT * FROM "people" WHERE (age >= 20)
>> Person.older_than(7)
  Person Load (0.000651)   SELECT * FROM "people" WHERE (age >= 7)

>> Person.female.adult
      Person Load (0.000494)   SELECT * FROM "people" WHERE ((age >= 20) AND ("people"."gender" = 2))

>> Person.older_than(10).female.name_start_with('松').count
  SQL (0.000375)   SELECT count(*) AS count_all FROM "people" WHERE (((name like '松%') AND ("people"."gender" = 2)) AND (age >= 10))

>> pp Person.scopes
{:male => #<Proc:0x017ead50@/Users/matsuda/railstokyo/edge080518/vendor/rails/activerecord/lib/active_record/named_scope.rb:87>,
 :name_start_with => #<Proc:0x017ead50@/Users/matsuda/railstokyo/edge080518/vendor/rails/activerecord/lib/active_record/named_scope.rb:87>,
 :female => #<Proc:0x017ead50@/Users/matsuda/railstokyo/edge080518/vendor/rails/activerecord/lib/active_record/named_scope.rb:87>,
 :adult => #<Proc:0x017ead50@/Users/matsuda/railstokyo/edge080518/vendor/rails/activerecord/lib/active_record/named_scope.rb:87>,
 :name_start_with_p => #<Proc:0x017ead50@/Users/matsuda/railstokyo/edge080518/vendor/rails/activerecord/lib/active_record/named_scope.rb:87>,
 :scoped => #<Proc:0x017ead50@/Users/matsuda/railstokyo/edge080518/vendor/rails/activerecord/lib/active_record/named_scope.rb:87>,
 :older_than => #<Proc:0x017ead50@/Users/matsuda/railstokyo/edge080518/vendor/rails/activerecord/lib/active_record/named_scope.rb:87>}

def self.search(params)
  exec_scopes = []
  if params[:is_male]
    exec_scopes << [:male, nil]
  end
  if params[:age_min]
    exec_scopes << [:older_than, params[:age_min]]
  end
  # (中略)
end

exec_scopes_string = exec_scopes.map {|s| "#{s[0]}(#{s[1]})"}.join('.')

eval "Person.#{exec_scopes_string}"

exec_scopes.inject(Person) {|p, s| scopes[s[0]].call p, *s[1]}

# 複数の引数。
    named_scope :age_between, lambda {|from, to| {:conditions => ['age between ? and ?', from, to]} }

def self.search(params)
      exec_scopes = []  # [実行するスコープ, [引数の配列]] な配列
      exec_scopes << [Person.scopes[:male], nil] if params[:is_male]
      exec_scopes << [Person.scopes[:older_than], params[:age_min]] if params[:age_min]
      exec_scopes << [Person.scopes[:age_between], [params[:age_between][0], params[:age_between][1]]] if params[:age_between]
      # あとは、こんな調子で他の paramsたちの解釈をずらずらと書く。ここでは省略。

      # これが呼び出し部
      exec_scopes.reverse.inject(Person) {|p, s| s[0].call p, *s[1]}.all
    end

>> Person.search({:is_male => true, :age_between => [10, 30]})
      Person Load (0.000518)   SELECT * FROM "people" WHERE (("people"."gender" = 1) AND (age between 10 and 30))