Rails 3, HABTM how to query with conditions - ruby-on-rails

Question

I have Awards and Categories, joined with Awards_Categories
I have 2 Categories.
I need to find all the Awards that have Category.id = 1, but not Category.id =2. Some categories have one or the other, some have just one. I want a list of the Awards that have category 1 but not category 2.
I have a scope:
scope :in_categories, lambda { |categories|
joins(:categories).
where(:awards_categories => { :category_id => categories } ).
select("DISTINCT awards.*")
}
And this works with a query like:
#awardsall = Award.in_categories([1 && 2]).order("name ASC")
I have tried
#awards_store = Award.in_categories([1]).order("name ASC")
With:
<% #awards_store.each do |store| %>
<li><%= link_to store.name, award_path(store), :title => store.info %> |
<% store.categories.each do |cat| %>
<%= cat.id%>
<% end %>
</li>
<% end %>
EDIT---
I know the block is not what I need. it is just my attempt at finding a way to make it work.
And while this lists all the awards, and all the award categories its still grabbing awards that have category.id = 2 because some awards have both
any ideas?

Answer 1

Sorry, didn't test it, but the main idea is to count the rows in the connecting table.
scope :in_categories, lambda { |*categories|
joins(:categories).
where(:awards_categories => { :category_id => categories } ).
where("(select count(distinct category_id) from awards_categories where category_id in (?)) = ?", categories, categories.size)
}
and use it this way:
#awardsall = Award.in_categories(1, 2).order("name ASC")
#awards_store = Award.in_categories(1).order("name ASC")
If you have a model for awards_categories, then it will look better:
scope :in_categories, lambda { |*categories|
joins(:categories).
where(:awards_categories => { :category_id => categories } ).
where("#{AwardCategory.where(:category_id => categories).count("distinct category_id").to_sql}=#{categories.size}")
}