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# frozen-string-literal: true
module Sequel
module Plugins
# This plugin implements a simple database-independent locking mechanism
# to ensure that concurrent updates do not override changes. This is
# best implemented by a code example:
#
# class Person < Sequel::Model
# plugin :optimistic_locking
# end
# p1 = Person[1]
# p2 = Person[1]
# p1.update(name: 'Jim') # works
# p2.update(name: 'Bob') # raises Sequel::NoExistingObject
#
# In order for this plugin to work, you need to make sure that the database
# table has a +lock_version+ column that defaults to 0. To change the column
# used, provide a +:lock_column+ option when loading the plugin:
#
# plugin :optimistic_locking, lock_column: :version
#
# This plugin relies on the instance_filters plugin.
module OptimisticLocking
# Exception class raised when trying to update or destroy a stale object.
Error = Sequel::NoExistingObject
def self.apply(model, opts=OPTS)
model.plugin(:optimistic_locking_base)
end
# Set the lock column
def self.configure(model, opts=OPTS)
model.lock_column = opts[:lock_column] || model.lock_column || :lock_version
end
module InstanceMethods
private
# Only update the row if it has the same lock version, and increment the
# lock version.
def _update_columns(columns)
lc = model.lock_column
lcv = get_column_value(lc)
columns[lc] = lcv + 1
super
set_column_value("#{lc}=", lcv + 1)
changed_columns.delete(lc)
nil
end
end
end
end
end
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