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# frozen-string-literal: true
module Sequel
module Plugins
# This plugin implements optimistic locking mechanism on Microsoft SQL Server
# using a timestamp/rowversion column to ensure that concurrent updates are
# detected and previous changes are not automatically overridden. This is
# best implemented by a code example:
#
# class Person < Sequel::Model
# plugin :mssql_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 column of timestamp or rowversion. The plugin uses a default
# name of timestamp for this columns, but you can override that using the
# :lock_column option:
#
# plugin :mssql_optimistic_locking, lock_column: :column_name
#
# This plugin relies on the instance_filters plugin.
module MssqlOptimisticLocking
# 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 (default: :timestamp)
def self.configure(model, opts=OPTS)
model.lock_column = opts[:lock_column] || :timestamp
end
module ClassMethods
# The timestamp/rowversion column containing the version for the current row.
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=>Sequel.blob(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
# Remove the lock column from the columns to update.
# SQL Server automatically updates the lock column value, and does not like
# it to be assigned.
def _save_update_all_columns_hash
v = @values.dup
cc = changed_columns
Array(primary_key).each{|x| v.delete(x) unless cc.include?(x)}
v.delete(model.lock_column)
v
end
# Add an OUTPUT clause to fetch the updated timestamp when updating the row.
def _update_without_checking(columns)
ds = _update_dataset
lc = model.lock_column
rows = ds.clone(ds.send(:default_server_opts, :sql=>ds.output(nil, [Sequel[:inserted][lc]]).update_sql(columns))).all
values[lc] = rows.first[lc] unless rows.empty?
rows.length
end
end
end
end
end
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