rewriting SQL query in rails ActiveRecord language ?

Is there any way to write this working query :

  Admin.select("DISTINCT `admins`.*").joins("LEFT OUTER JOIN
`admins_roles` ON `admins_roles`.`admin_id` =
`admins`.`id`").joins("LEFT OUTER JOIN `roles` ON
`admins_roles`.`role_id` = `roles`.`id`").where("roles.resource_type
IS NULL AND roles.name = ?", "manager")

in Rails ActiveRecord "dialect" ?

I tried ( Admins and Roles are associated w an HMABT association

Admin.joins(:roles).where(:roles => {:resource_type => "", :name
=> :manager})
this doesn't work

If I only write :
Admin.joins(:roles).where(:roles => {:name => :manager})
this works, but I get all ;manager with any resource_type

thanks for feedback

just SOLVED it ... :resource_type => "" is wrong should
be :resource_type => nil,
I'll change my glasses