Eager Loading with "has many through" -- do I need Arel? - ruby-on-rails

Question

I have three tables: users, members, projects. The middle is a join table expressing a has-many-through between the other two tables; and it has some attributes of interest, including join_code and activated.
More expansively:
class User < ActiveRecord::Base
has_many :members
has_many :projects, :through => :members
end
class Member < ActiveRecord::Base
belongs_to :user
belongs_to :project
# has a column called join_code
# has a column called activated
# Note that this class can be thought of as "membership"
end
class Project < ActiveRecord::Base
has_many :members
has_many :users, :through => :members
end
Goal: Given a particular user, I want a query that will get all the projects, and eager load only the member records that link those projects to the user.
So far I have this method in user.rb that does a query:
def live_projects
self.projects.order("projects.name").includes(:members).where(:members => {:join_code => nil, :activated => true})
end
But it's not enough. I'd like to then be able to do this in the view code:
<% current_user.live_projects.each do |project| %>
<li project_id="<%= project.id %>">
<% member = project.member %>
(Do something with that member record here)
<%= project.name %>
<% end %>
</li>
<% end %>
Here, normally, I'd have project.members, but in my context I'm only interested in that one member record that links back to the user.
Here is what I think the raw SQL should look like
select projects.*, members.*
from projects inner join members on projects.id = members.project_id
where members.user_id = X and members.join_code is null and members.activated = 't';
How to do that in Arel (or ActiveRecord)?

Answer 1

I may have something of an answer here, namely that the ActiveRecord code I wrote seems pretty reasonable. Again, here's that query:
def live_projects
self.projects.order("projects.name").includes(:members).where(:members => {:join_code => nil, :activated => true})
end
On a run through the UI with sample data it generates this output from Rails server:
Project Load (0.6ms) SELECT "projects".* FROM "projects" INNER JOIN "members" ON "projects".id = "members".project_id WHERE "members"."join_code" IS NULL AND "members"."activated" = 't' AND (("members".user_id = 3)) ORDER BY projects.name
Member Load (2.0ms) SELECT "members".* FROM "members" WHERE ("members".project_id IN (50,3,6,37,5,1))
Then later in the view code I can do this:
<% current_user.live_projects.each do |project| %>
<li project_id="<%= project.id %>" class="<%= 'active' if project == #project %>">
<% member = project.members.detect { |member| member.user_id == current_user.id } %>
(Do something with that member record here)
</li>
<% end %>
That expression to get the member record is pretty ugly in the view, but select is an Array method, not a query, and no extra DB hits other than the two shown above appear in the output from Rails server. Thus I guess my n+1 problem is solved.

Answer 2

Add an association called live_members on the Project class.
class Project < ActiveRecord::Base
has_many :live_members, :class_name => "Member",
:conditions => {:join_code => nil, :activated => true}
has_many :members
has_many :users, :through => :members
end
Add an association called live_projects on the User class.
class User < ActiveRecord::Base
has_many :members
has_many :projects, :through => :members
has_many :live_projects, :through => :members, :source => :project,
:include => :live_member, :order => "projects.name"
end
Now you can:
user.live_projects

Answer 3

It seems that you expect there to be at most one active member linking each user to a project. If this is the case the following should work:
In member.rb:
scope :live, where(:join_code => nil, :activated => true)
In user.rb:
def live_projects_with_members
members.live.includes(:project).group_by(&:project)
end
In your view:
<% current_user.live_projects_with_members.each do |project, members| %>
<% member = members.first %>
<li project_id="<%= project.id %>" class="<%= 'active' if project == #project %>">
(Do something with that member record here)
</li>
<% end %>
If you then want to add an extra join for your usage stats you can do this:
def live_projects_with_members
members.live.includes(:project, :stats).group_by(&:project)
end