resort

Resort provides sorting capabilities to your Rails (4+) models.

Install

$ gem install resort

Or in your Gemfile:

gem 'resort'

Rationale

Most other sorting plugins work with an absolute position attribute that sets the weight of a given element within a tree. This field has no semantic sense, since "84" by itself gives you absolutely no information about an element's position or its relations with other elements of the tree.

Resort is implemented like a linked list, rather than relying on absolute position values. This way, every model references a next element, which seems a bit more sensible :)

Usage

First, run the migration for the model you want to Resort:

$ rails generate resort:migration product
$ rake db:migrate

Then in your Product model:

class Product < ActiveRecord::Base
  resort!
end

NOTE: By default, Resort will treat all products as a single big tree. If you wanted to limit the tree scope, i.e. treating every ProductLine as a separate tree of sortable products, you must override the siblings method:

class Product < ActiveRecord::Base
  resort!

  def siblings
    # Tree contains only products from my own product line
    self.product_line.products
  end
end

Concurrency

Multiple users modifying the same list at the same time could be a problem, so it's always a good practice to wrap the changes in a transaction:

Product.transaction do
  my_product.append_to(another_product)
end

API

Every time a product is created, it will be appended after the last element.

Moreover, now a product responds to the following methods:

first? — Returns true if the element is the first of the tree.
append_to(other_element) — Appends the element after another element.
prepend — Moves the element to the beginning of the list (sets it as first).
next — Returns the next element in the list.
previous — Returns the previous element in the list.

And the class Product has a new scope named ordered that returns the products in order.

Examples

Given our Product example defined before, we can do things like:

Getting products in order:

Product.first_in_order # returns the first ordered product.
Product.last_in_order # returns the last ordered product.
Product.ordered # returns all products ordered as an Array, not a Relation!

Find ordered products with scopes or conditions:

Product.where('price > 10').ordered # => Ordered array of products with price > 10
Product.with_custom_scope.ordered # => Ordered array of products with your custom conditions

Modify the list of products:

product = Product.create(:name => 'Bread')
product.first? # => true

another_product = Product.create(:name => 'Milk')
yet_another_product = Product.create(:name => 'Salami')

yet_another_product.append_to(product) # puts the products right after the first one

Product.ordered.map(&:name) # => ['Bread', 'Salami', 'Milk']

Check neighbours:

product = Product.create(:name => 'Bread')
second_product = Product.create(:name => 'Milk')
third_product = Product.create(:name => 'Salami')

second_product.previous.name # => 'Bread'
second_product.next.name # => 'Salami'

third_product.next # => nil

Maybe you need different orders depending on the product vendor:

class Product < ActiveRecord::Base
  resort!

  belongs_to :vendor

  def siblings
    self.vendor.products
  end
end

bread = Product.create(:name => 'Bread', :vendor => Vendor.where(:name => 'Bread factory').first)
bread.first? # => true

milk = Product.create(:name => 'Milk', :vendor => Vendor.where(:name => 'Cow world').first)
milk.first? # => true

# bread and milk aren't neighbours

Under the hood

Run the test suite by typing:

rake

You can also build the documentation with the following command:

rake docs

Note on Patches/Pull Requests

Fork the project.
Make your feature addition or bug fix.
Add tests for it. This is important so I don't break it in a future version unintentionally.
Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
Send us a pull request. Bonus points for topic branches.

usetrio/resort