acts_as_list methods on has_many through

[lsarni]

I'm using a has_many through relationship with a join table, like it was explained in some other issues and Stackoverflow.

This is how my models look like:

class Update < ActiveRecord::Base
  has_many :links, through: 'update_links'
  has_many :update_links
end

class Link < ActiveRecord::Base
  has_many :collections, through: 'update_links', foreign_key: 'update_id'
  has_many :update_links
end

class UpdateLink < ActiveRecord::Base
  default_scope { order :position }
  belongs_to :collection, foreign_key: 'update_id', class_name: 'Update'
  belongs_to :link
  acts_as_list scope: :update
end

But if I try to use any of the acts_as_list methods like this:

update.links.last.move_to_top
  Link Load (1.1ms)  SELECT  "links".* FROM "links" INNER JOIN "update_links" ON "links"."id" = "update_links"."link_id" WHERE "update_links"."update_id" = $1  ORDER BY "update_links"."position" DESC, update_links.position DESC LIMIT 1  [["update_id", 1]]
NoMethodError: undefined method `position' for #<Link:0x007fcd53f93210>

I saw this workaround but since it's quite an old post I was wondering if the library has been extended to be usable on this cases.

I made some changes to the workaround so it works with all the methods and had to add a primary_key to my join table (since many of the list methods call it):

  def method_missing(symbol, *args, &block)
    if acts_as_list_method?(symbol)
      pass_method_to_update_links(symbol, args.shift, *args)
    else
      super
    end
  end

  def pass_method_to_update_links(symbol, link, *args)
    raise "A link is needed" unless link.kind_of? Link
    move_link = self.update_links.find_by(link: link)
    move_link.send(symbol, *args) if move_link
  end

  def acts_as_list_method?(symbol)
    ActiveRecord::Acts::List::InstanceMethods.instance_methods.include?(symbol.to_sym)
  end

That way instead of doing list_item.move_higher I do collection.move_higher(list_item).

But if there is a built in way of doing this I would much prefer that.

[brendon]

Hi @lsarni, that's a mind bender. Do you only have a position column on the join table? or also on the links table?

acts_as_list assumes the column exists on the table that the model represents. And you're right, I'm pretty sure it also assumes a primary key column, though that might be more via rails.

[lsarni]

I have the position column on the join table, it wouldn't make sense for it to be on the links table since a link can be in a different position depending on the update.

And the primary key is requested in quite a few of the list methods defined by the library, for example higher_items here

With the stated workaround I managed to get al the methods working correctly. Maybe, if there isn't an out of the box solution, adding a flag to state that we are working on a join table and include this behaviour could be a good improvement.

[brendon]

I see, what if you just called the methods directly on the join association:

link = update.links.last # Or whatever you want to select
update.update_links.where(link: link).first.move_to_top

It's a bit messy, but should do the trick. What do you think?

[lsarni]

I have tried it out, and I get this error:

NoMethodError:   UpdateLink Load (0.7ms)  SELECT "update_links".* FROM "update_links" WHERE "update_links"."update_id" = $1 AND "update_links"."link_id" = 10805  ORDER BY "update_links"."position" ASC  [["update_id", 1]]
undefined method `move_to_top' for #<UpdateLink::ActiveRecord_AssociationRelation:0x007f9bb07902e0>
	from /Users/lucia/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/activerecord-4.2.5/lib/active_record/relation/delegation.rb:136:in `method_missing'
	from /Users/lucia/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/activerecord-4.2.5/lib/active_record/relation/delegation.rb:99:in `method_missing'
	from (irb):11
	from /Users/lucia/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/console.rb:110:in `start'
	from /Users/lucia/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/console.rb:9:in `start'
	from /Users/lucia/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:68:in `console'
	from /Users/lucia/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
	from /Users/lucia/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/railties-4.2.5/lib/rails/commands.rb:17:in `<top (required)>'
	from bin/rails:4:in `require'
	from bin/rails:4:in `<main>'

The same happens for the other methods.

[swanandp]

acts_as_list scope: :update

Shouldn't this be acts_as_list scope: :collection ?

undefined method `move_to_top' for #UpdateLink::ActiveRecord_AssociationRelation:0x007f9bb07902e0

You need update.update_links.where(link: link).first.move_to_top

.where returns an collection object (it could well be a collection of one item, as in this case), but to get to the actual record, you need to call .first.

[lsarni]

@swanandp you're right, I was missing the first.

It works regardless of whether the scope is :update or :collection.

It is pretty messy, but it's is exactly what the workaround does so I'm going to keep that on my project so it looks neater. But feel free to close the issue.

[swanandp]

Glad it's working.

[brendon]

I think the scope should be :update since that's the foreign key name (update_id). That's for spotting my error @swanandp :D

[lsarni]

I just noticed that this won't work for insert_at since in this case update.update_links.where(link: link) returns nil because the link isn't part of the list yet.

[brendon]

Instead of using insert_at just specify the position you want to create the record at. Other items will be shuffled around accordingly when the item is created.