The Sequel Gem: Everything About Scopes

sequel_scopes.rb

# (I recommend understanding the basics of this first: http://sequel.jeremyevans.net/rdoc/files/doc/object_model_rdoc.html)

# Extending the underlying dataset  (http://sequel.jeremyevans.net/rdoc/files/README_rdoc.html#label-Extending+the+underlying+dataset)

# The recommended way to implement table-wide logic by defining methods on the dataset using dataset_module:

    class Post < Sequel::Model
      dataset_module do
        def posts_with_few_comments
          where{num_comments < 30}
        end

        def clean_posts_with_few_comments
          posts_with_few_comments.delete
        end
      end
    end

# This allows you to have access to your model API from filtered datasets as well:

    Post.where(:category => 'ruby').clean_posts_with_few_comments

# Sequel models also provide a subset class method that creates a dataset method with a simple filter:

    class Post < Sequel::Model
      subset(:posts_with_few_comments){num_comments < 30}
      subset :invisible, Sequel.~(:visible)
    end

# Model  ((http://www.rubydoc.info/gems/sequel/Sequel/Model))

  DATASET_METHODS   : Class methods added to model that call the method of the same name on the dataset
                      Dataset::ACTION_METHODS + Dataset::QUERY_METHODS

# Model::ClassMethods  (http://www.rubydoc.info/gems/sequel/Sequel/Model/ClassMethods)

  #subset(name, *args, &block) ⇒ Object

#   Sets up a dataset method that returns a filtered dataset. Sometimes thought of as a scope, and like most dataset methods, they can be chained. For example:

      Topic.subset(:joes, :username.like('%joe%'))
      Topic.subset(:popular){num_posts > 100}
      Topic.subset(:recent){created_on > Date.today - 7}

#   Allows you to do `Topic.joes.recent.popular` to get topics with a username that includes joe that have more than 100 posts and were created less than 7 days ago.
#   Both the args given and the block are passed to Dataset#filter.
#   This method creates dataset methods that do not accept arguments.
#   To create dataset methods that accept arguments, you should use define a method directly inside a #dataset_module block.

# Model::DatasetModule  (http://www.rubydoc.info/gems/sequel/Sequel/Model/DatasetModule)

#  This Module subclass is used by Model.dataset_module to add dataset methods to classes.
#  It adds a couple of features standard Modules, allowing you to use the same subset method you can call on Model,
#    as well as making sure that public methods added to the module automatically have class methods created for them.

  #subset(name, *args, &block) ⇒ Object

#    Define a named filter for this dataset, see Model.subset for details.

# ActiveRecord -- named_scope  (http://sequel.jeremyevans.net/rdoc/files/doc/active_record_rdoc.html#label-named_scope)

#  For a pure filter, you can use subset:

    Album.subset(:debut, :position => 1)
    Album.subset(:gold){copies_sold > 500000}

#  For anything more complex, you can use dataset_module:

    Album.dataset_module do
      def by_artist(artist_id)
        where(:artist_id=>artist_id)
      end

      def by_release_date
        order(:release_date)
      end
    end