ActiveRecord Count Question

Rails
1

In the language of my domain, a Community has many Media and a Media has
many Viewings. I’m drawing a blank trying to find a clean way to get the
count of unviewed Media by Community for a User.

def community
has_many :medias
end

def media
has_many :viewings
belongs_to :media
end

def viewing
belongs_to :media
belongs_to :user
end

def user
has_many :viewings
end

The trouble I’m having is finding a way to represent “not in” or “not
exists” sql constructs in an ActiveRecord query. If I were to manually
write out the query for a single community it might look like:

select count(*) from media where community_id = @community_id and not
exists (select * from viewings where user_id = @user_id and media_id =
media.media_id)

Any ideas on how to convert this into a beautiful, one-line statement in
ActiveRecord would be much appreciated.

2

If the number of media is small, you might just take the difference of
the “total media” and the “media viewed …”

(What are these media?)

Stephan

Jeff wrote:

In the language of my domain, a Community has many Media and a Media has
many Viewings. I’m drawing a blank trying to find a clean way to get the
count of unviewed Media by Community for a User.

def community
has_many :medias
end

def media
has_many :viewings
belongs_to :media
end

def viewing
belongs_to :media
belongs_to :user
end

def user
has_many :viewings
end

The trouble I’m having is finding a way to represent “not in” or “not
exists” sql constructs in an ActiveRecord query. If I were to manually
write out the query for a single community it might look like:

select count(*) from media where community_id = @community_id and not
exists (select * from viewings where user_id = @user_id and media_id =
media.media_id)

Any ideas on how to convert this into a beautiful, one-line statement in
ActiveRecord would be much appreciated.