Find unused items

This works, but I am sure there is a better way todo this:

  # GET /posts/1/edit
  def edit
    @post = Post.find(params[:id])
    # Find user galleries that have not been used in posts yet
    usergalleries = Array.new
    @post.user.galleries.each do |pug|
      usergalleries << pug.id
    end
    userpostgalleries = Array.new
    @post.user.posts.each do |pup|
      userpostgalleries << pup.gallery_id
    end
    aug = usergalleries - userpostgalleries
    @availableusergalleries = @post.user.galleries.find
(:all, :conditions => { :id => aug })
  end

Any ideas?

Regards
Arwed

Quoting arwed <af@bbp.biz>:

This works, but I am sure there is a better way todo this:

  # GET /posts/1/edit
  def edit
    @post = Post.find(params[:id])
    # Find user galleries that have not been used in posts yet
    usergalleries = Array.new
    @post.user.galleries.each do |pug|
      usergalleries << pug.id
    end
    userpostgalleries = Array.new
    @post.user.posts.each do |pup|
      userpostgalleries << pup.gallery_id
    end
    aug = usergalleries - userpostgalleries
    @availableusergalleries = @post.user.galleries.find
(:all, :conditions => { :id => aug })
  end

Any ideas?

# @post = Post.find(params[:id])
     @post = Post.find(params[:id], :include => {:user => [:galleries, :posts]})

# One database call instead of many. I think this is correct form, but
# have no easy way to test it.

# # Find user galleries that have not been used in posts yet
# usergalleries = Array.new
# @post.user.galleries.each do |pug|
# usergalleries << pug.id
# end
     user_galleries = @post.user.galleries.map{|pug| pug[:id]}

# I find pug[:id] more reliable than pug.id; the latter in some contexts is
# interpreted as the Object id, instead of the primary key/ID from the
# database and a deprecation warning is given.

# userpostgalleries = Array.new
# @post.user.posts.each do |pup|
# userpostgalleries << pup.gallery_id
# end
     user_post_galleries = @post.user.posts.map{|pup| pup.gallery_id}

     aug = usergalleries - userpostgalleries
# @availableusergalleries = @post.user.galleries.find(:all, :conditions =>
{ :id => aug })
     @availableusergalleries = @post.user.galleries.find(aug)

# ActiveRecord.find will take an array of IDs.

Another way that takes less memory (if speed is of more concern, benchmark
both):

    aug = @post.user.galleries.map{|pug| pug[:id]}
    @post.user.posts.each{|pup| aug.delete(pup.gallery_id)}

    @availableusergalleries = Gallery.find(aug)

HTH,
  Jeffrey

Hi Jeffrey,

thanks a lot for your help.
You made my day!

Regards
Arwed