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Created August 31, 2018 14:25
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The Sequel Gem: Everything About Scopes
# (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
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