在Ruby on Rails中指定关系的条件

has_many :administrators, :class_name => \"User\", :conditions => \"role_id = 4\"

\"role_id = 4\"

SELECT *
FROM users u, roles r
WHERE u.role_id = r.id
AND r.role = \"Admin\"

has_many :administrators, :class_name => \"User\", :conditions => { :role => {:name => \"Admin\"}}

has_many :administrators, :class_name => \"User\", :conditions => {:roles => {:name => \"Admin\"}}, :include => :role

has_many :administrators, :class_name => \"User\", :conditions => \"role_id = #{Role.find(:name => \'Admin\')}\"