gistfile1.rb

class User
  has_many :group_roles
  has_many :groups, :through=>:group_roles
end

class GroupRole
  belongs_to :user
  belongs_to :group
end

class Group
  has_many :group_roles
  has_many :users, :through=>:group_roles
end

group_arel = Group.where(:active=>true).where(:important=>'very')
groups = group_arel.to_a # returns [group, group, group]

user_sql = group_arel.joins(:users).select("users.*").to_sql
User.find_by_sql(user_sql) # return [user, user, user] for all the users of all the groups on #17

# What I'd like to be able to do
user_arel = User.take_everything_but_the_select_from(group_arel)
amended_user_arel = user_arel.where(:name=>"bob")
amended_user_arel.to_a # returns [user, user, user]

The group_arel on #16 represents a complex query that, when finally executed, returns all the Groups that match. However, the same query can be used to return all Users of all matching Groups by changing the select clause, as shown on line 19-20, but that's returning an array so it's not possible to do any further chaining on the arel.

What I'd like to be able to do is change the 'class' of the query object to return instances of User rather than Group. Is this possible?