Given these models
class Category < ActiveRecord
has_many :category_assignments
has_many :posts, :through => :category_assignments
end
class CategoryAssignment < ActiveRecord::Base
belongs_to :post
belongs_to :category
# Has boolean column 'featured'
end
class Post < ActiveRecord::Base
has_many :category_assignments
has_many :categories, :through => :category_assignments
end
I want to add a named_scope to Post that will return all featured
posts. But the semantics of this named_scope vary depending upon
whether I am calling the named scope on Post or on category.posts:
Post.featured
is simple enough. The definition
named_scope :featured,
:joins => :category_assignments,
:conditions => {:category_assignments.featured => true }
will return all posts for which any associated category_assignment
record has featured = true.
But when I take a category instance and call category.posts.featured I
want to get all of the posts which are featured *in that category*,
which requires restricting by category_id. To do this properly the
named_scope code needs to be able to determine whether it's being
called in a context in which category_assignments has already been
joined (and/or whether a category_id is specified in the conditions).
I have not figured out how to do this.
If I can detect whether or not the named_scope is being called within
the context of an association then I can do something like the
following, which changes named_scope semantics based on whether or not
a category _argument_ is explicitly provided:
named_scope :featured, lambda { |*args|
if (category = args.first)
{ :joins => :category_assignments,
:conditions => {:category_id => category.id,
:featured => true} }
else
{ :joins => :category_assignments,
:conditions => {:featured => true} }
end
}
Is there some way to inspect a joins or conditions hash to determine
association state from within a named_scope? And if so, is it reliable
regardless of the order of named_scope stacking (i.e. will it work for
either category.posts.other.named.scopes.featured or
category.posts.featured.other.named.scopes)?
Thanks,
Sven
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