module Sequel::Plugins::DefDatasetMethod::ClassMethods

If a block is given, define a method on the dataset (if the model currently has an dataset) with the given argument name using the given block. Also define a class method on the model that calls the dataset method. Stores the method name and block so that it can be reapplied if the model’s dataset changes.

If a block is not given, just define a class method on the model for each argument that calls the dataset method of the same argument name.

Using dataset_module is recommended over using this method. In addition to allowing more natural ruby syntax for defining methods manually, it also offers numerous helper methods that make defining common dataset methods more easily, as well as supporting dataset caching (assuming the arguments allow it).

# Add new dataset method and class method that calls it
Artist.def_dataset_method(:by_name){order(:name)}
Artist.where(Sequel[:name].like('A%')).by_name
Artist.by_name.where(Sequel[:name].like('A%'))

# Just add a class method that calls an existing dataset method
Artist.def_dataset_method(:paginate)
Artist.paginate(2, 10)

   # File lib/sequel/plugins/def_dataset_method.rb
50 def def_dataset_method(*args, &block)
51   raise(Error, "No arguments given") if args.empty?
52 
53   if block
54     raise(Error, "Defining a dataset method using a block requires only one argument") if args.length > 1
55     dataset_module{define_method(args.first, &block)}
56   else
57     args.each{|arg| def_model_dataset_method(arg)}
58   end
59 end

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, Sequel[: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#where.

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.

   # File lib/sequel/plugins/def_dataset_method.rb
83 def subset(*args, &block)
84   dataset_module{subset(*args, &block)}
85 end