move_lower and move_higher not working returning nil

[shaileshkalamkar]

Hi,

I am using Rails 3.2.6 application with acts_as_list(0.1.6) gem included in my Gemfile.

I have the code as follows

class Product < ActiveRecord::Base
  attr_accessible :name, :price
  has_many :product_stores
  has_many :stores, :through => :product_stores, :order => 'product_stores.position'
end

class ProductStore < ActiveRecord::Base
  attr_accessible :position, :product_id, :store_id
  default_scope :order => 'position'

  belongs_to :store
  belongs_to :product

  acts_as_list :scope => :product
end

class Store < ActiveRecord::Base
  attr_accessible :description, :name
  has_many :product_stores
  has_many :products, :through => :product_stores, :order => 'product_stores.position'
end

I have position(integer) column in the product_stores table . But the move_lower and move_higher functions does not work returning nil and the product is not moved to any position without updating the position. e.g

ruby-1.9.2-p290 :008 > store.product_stores.where(:product_id => 2).first.move_lower
  ProductStore Load (0.2ms)  SELECT `product_stores`.* FROM `product_stores` WHERE `product_stores`.`store_id` = 1 AND `product_stores`.`product_id` = 2 LIMIT 1
  ProductStore Load (0.3ms)  SELECT `product_stores`.* FROM `product_stores` WHERE (`product_stores`.`product_id` = 2 AND position = 2) ORDER BY position LIMIT 1
 => nil 
ruby-1.9.2-p290 :009 > 

Hw to resolve it ?

[matthewfarrell]

I too had this problem after setting up acts_as_list when there was existing data in the table. It appears that move_lower/move_higher will not move an item if the position column value is null, or if only one item has a position. This makes sense, but is not immediately obvious. To resolve this, I set a default position for all items using a migration:

execute "UPDATE sortable_table SET position = id"

Source: http://nicholshayes.co.uk/blog/?p=344

[swanandp]

@shaileshparamisoft I think upgrading to latest should solve your problem.

[swanandp]

But if not, let me know.

[shaileshkalamkar]

@swanandp Yes, the issue has been resolved.
Thanks for you reply.

[daz]

I'm still getting nil when setting it up, because all my position columns are nil.

[mkolodziej]

I had a Category hierarchy in my app and had the same problem with null position values. I solved it by adding this method to the migration that created the position column:

  update_position_recursively(Category.roots)

  def update_position_recursively(categories)
    categories.each_with_index do |cat, idx|
      cat.update_attribute(:position, idx)
      update_position_recursively(cat.subcategories) unless cat.subcategories.empty?
    end
  end

This is assuming Category.roots would return all roots and that I have has_many :subcategories ... in my Category class

[redbar0n]

I fixed this problem by making a rake task (as DB updates generally shouldn't be done in migrations). See: https://stackoverflow.com/a/15531843/380607