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# frozen-string-literal: true
module Sequel
module Plugins
# The accessed_columns plugin records which columns have been
# accessed for a model instance. This is useful if you are
# looking to remove other columns from being SELECTed by the
# dataset that retrieved the instance, which can significantly
# improve performance:
#
# a = Album[1]
# a.accessed_columns # []
# a.name
# a.accessed_columns # [:name]
# a.artist_id
# a.accessed_columns # [:name, :artist_id]
#
# Note that this plugin should probably not be used in production,
# as it causes a performance hit.
#
# Usage:
#
# # Make all model subclass instances record accessed columns (called before loading subclasses)
# Sequel::Model.plugin :accessed_columns
#
# # Make the Album instances record accessed columns
# Album.plugin :accessed_columns
module AccessedColumns
module InstanceMethods
# Record the column access before retrieving the value.
def [](c)
(@accessed_columns ||= {})[c] = true unless frozen?
super
end
# Clear the accessed columns when saving.
def after_save
super
@accessed_columns = nil
end
# The columns that have been accessed.
def accessed_columns
@accessed_columns ? @accessed_columns.keys : []
end
# Copy the accessed columns when duping and cloning.
def initialize_copy(other)
other.instance_variable_set(:@accessed_columns, Hash[@accessed_columns]) if @accessed_columns
super
end
private
# Clear the accessed columns when refreshing.
def _refresh(_)
@accessed_columns = nil
super
end
end
end
end
end
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