Sending objects values as IN statement in Rails - ruby-on-rails

Question

I'm working on a Newsfeed action. I have active friendships and i would like to find the posts only of those friendships to create the newsfeed.
This is the code i currently have:
#active_friendships = current_user.active_friendships
#posts = Post.where({ :user_id => [5,8,16] }).order("created_at DESC")
I don't know how to send the #active_friendships.user_id values to the IN in the second line. At the moment the code is only worked because it has hardcoded the user_id of my active friends (5,8,16).
(If i do a debug #active_friendships) i get the 3 objects with their ids, but i still don't know how to send them to the IN in the second line as the ids to look for.
--
- !ruby/object:Friendship
attributes:
created_at: 2010-10-06 22:27:54.620007
updated_at: 2010-10-07 00:19:10.329799
id: 182
user_id: 8
status: 1
friend_id: 5
attributes_cache: {}
changed_attributes: {}
destroyed: false
marked_for_destruction: false
new_record: false
previously_changed: {}
readonly: false
- !ruby/object:Friendship
attributes:
created_at: 2010-10-07 19:13:10.617959
updated_at: 2010-10-07 19:13:17.097514
id: 192
user_id: 16
status: 1
friend_id: 5
attributes_cache: {}
changed_attributes: {}
destroyed: false
marked_for_destruction: false
new_record: false
previously_changed: {}
readonly: false
- !ruby/object:Friendship
attributes:
created_at: 2010-10-10 04:12:48.931120
updated_at: 2010-10-10 04:12:56.960752
id: 214
user_id: 8
status: 1
friend_id: 5
attributes_cache: {}
changed_attributes: {}
destroyed: false
marked_for_destruction: false
new_record: false
previously_changed: {}
readonly: false
Many thanks in advance

Answer 1

You can try this:
#posts = Post.where(:user_id => #active_friendships.map(&:friend_id)
).order("created_at DESC"
But better way of implementing this is to add an association
class User
has_many :active_friendships, :class_name => "Friendship", :conditions = {...}
has_many :active_friend_posts, :through => :active_friendships,
:source => :friend_posts
end
class Friendship
belongs_to :user
belongs_to :friend, :class_name => "User"
has_many :friend_posts, :class_name => "Post",
:primary_key => :freind_id, :foreign_key => :post_id
end
class Post
belongs_to :user
end
Now you can do the following:
current_user.active_friend_posts.order("created_at DESC")

Answer 2

I'm new at this, but could you collect all of the Friendship.user_id's into an array and then pass that in the where clause?
#friends_userids = current_user.active_friendships.collect { |x| x.user_id }
#posts = Post.where({ :user_id => #friends_userids }).order("created_at DESC")

Answer 3

I had a similar issue. This is how I implemented it:
ids = #active_friendships.map { |x| x.user_id }
ids = ids.join(",")
#posts = Post.all(:conditions => ["posts.user_id in (#{ids})"]).order("created_at DESC")
This creates an array of all user IDs from #active_friendships and then joins them into a string with a comma as a separator. Then I simply passed this to the :conditions parameter.
It's not as elegant as I like but it works.
Hope this helps.

Answer 4

Rails has a special method for getting an array of associated ids. You should be able to do this in one line something like this:
#posts = Post.where(:user_id => current_user.active_friendship_ids).order("created_at DESC")
Whenever you're dealing with has_many and has_many :through relationships, you have access to the association_ids method, which won't return the full objects. Check out the full api here:
http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html