Help with ActiveRecord query - ruby-on-rails

Question

Models:
class User < ActiveRecord::Base
has_many :attendances
has_many :courses, :through => :attendances
end
class Course < ActiveRecord::Base
has_many :attendances
end
class Attendance < ActiveRecord::Base
belongs_to :user
belongs_to :course
end
Migrations:
create_table(:users) do |t|
t.string :name
end
create_table(:courses) do |t|
t.string :name
end
create_table(:attendances) do |t|
t.references :user, :course
t.date :date
end
Question
I would like to query:
a list of all courses
the date of a given user's last attendance (if any) for each course
What is the best way to tie the following together into a single query?
#courses = Course.all
#user = User.first
#attendances = #user.attendances.group('course_id').order('date DESC')
Note that there is a requirement to include courses that a user has not yet attended.
Any advice much appreciated.
Update
The result I am looking for is as follows:
Course Last attended
===============================
Some course 2011-03-09
More training Not Attended
Another course 2010-12-25
In SQL, I would write this query as:
SELECT * FROM courses AS c
LEFT OUTER JOIN attendances AS a ON a.course_id=c.id
WHERE a.user_id=1
GROUP BY a.course_id
ORDER BY a.date DESC;
I could always execute this SQL from within Rails, but I would prefer to avoid this and do things "the Rails way" if possible.

Answer 1

The "Rails-Way" is to define small finders in the model and then to chain them in the controllers.
In class Attendance you could define a new method
def self.last_attendance
maximum("date")
end
In class Corse ...
def self.ordered
order("name DESC")
end
And so on. In the controller then, you use them in different combinations. The big advantage of this approach is
Reusability of finder methods
Decoupling of classes
Better readability of code

Answer 2

Your has_many through relation should be like this:
class User < ActiveRecord::Base
has_many :attendances
has_many :courses, :through => :attendances
end
class Course < ActiveRecord::Base
has_many :attendances
has_many :users, :through => :attendances
end
class Attendance < ActiveRecord::Base
belongs_to :user
belongs_to :course
end
And please explain your problem. Because
#user.courses will give you only related courses
Course.all will give you all courses
Edited:
Course.find(:all, :joins => 'LEFT OUTER JOIN attendances ON attendances.course_id =
courses.id', :conditions => ['attendances.user_id = ?', 1], :group =>
'attendances.course_id', :order => 'attendances.date DESC')
I hope it will work for you.