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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::Plugins::OptimisticLocking::Error
#
# In order for this plugin to work, you need to make sure that the database
# table has a +lock_version+ column (or other column you name via the lock_column
# class level accessor) that defaults to 0.
#
# 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
# Load the instance_filters plugin into the model.
def self.apply(model, opts=OPTS)
model.plugin :instance_filters
end
# Set the lock_column to the :lock_column option, or :lock_version if
# that option is not given.
def self.configure(model, opts=OPTS)
model.lock_column = opts[:lock_column] || :lock_version
end
module ClassMethods
# The column holding the version of the lock
attr_accessor :lock_column
Plugins.inherited_instance_variables(self, :@lock_column=>nil)
end
module InstanceMethods
# Add the lock column instance filter to the object before destroying it.
def before_destroy
lock_column_instance_filter
super
end
# Add the lock column instance filter to the object before updating it.
def before_update
lock_column_instance_filter
super
end
private
# Add the lock column instance filter to the object.
def lock_column_instance_filter
lc = model.lock_column
instance_filter(lc=>get_column_value(lc))
end
# Clear the instance filters when refreshing, so that attempting to
# refresh after a failed save removes the previous lock column filter
# (the new one will be added before updating).
def _refresh(ds)
clear_instance_filters
super
end
# 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)
end
end
end
end
end
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