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|
# frozen-string-literal: true
module Sequel
module Plugins
# This plugin allows you to add filters on a per object basis that
# restrict updating or deleting the object. It's designed for cases
# where you would normally have to drop down to the dataset level
# to get the necessary control, because you only want to delete or
# update the rows in certain cases based on the current status of
# the row in the database. The main purpose of this plugin is to
# avoid race conditions by relying on the atomic properties of database
# transactions.
#
# class Item < Sequel::Model
# plugin :instance_filters
# end
#
# # These are two separate objects that represent the same
# # database row.
# i1 = Item.first(id: 1, delete_allowed: false)
# i2 = Item.first(id: 1, delete_allowed: false)
#
# # Add an instance filter to the object. This filter is in effect
# # until the object is successfully updated or deleted.
# i1.instance_filter(delete_allowed: true)
#
# # Attempting to delete the object where the filter doesn't
# # match any rows raises an error.
# i1.delete # raises Sequel::NoExistingObject
#
# # The other object that represents the same row has no
# # instance filters, and can be updated normally.
# i2.update(delete_allowed: true)
#
# # Even though the filter is now still in effect, since the
# # database row has been updated to allow deleting,
# # delete now works.
# i1.delete
#
# This plugin sets the require_modification flag on the model,
# so if the model's dataset doesn't provide an accurate number
# of matched rows, this could result in invalid exceptions being raised.
module InstanceFilters
# Exception class raised when updating or deleting an object does
# not affect exactly one row.
Error = Sequel::NoExistingObject
# Set the require_modification flag to true for the model.
def self.configure(model)
model.require_modification = true
end
module InstanceMethods
# Clear the instance filters after successfully destroying the object.
def after_destroy
super
clear_instance_filters
end
# Clear the instance filters after successfully updating the object.
def after_update
super
clear_instance_filters
end
# Freeze the instance filters when freezing the object
def freeze
instance_filters.freeze
super
end
# Add an instance filter to the array of instance filters
# Both the arguments given and the block are passed to the
# dataset's filter method.
def instance_filter(*args, &block)
instance_filters << [args, block]
end
private
# If there are any instance filters, make sure not to use the
# instance delete optimization.
def _delete_without_checking
if @instance_filters && !@instance_filters.empty?
_delete_dataset.delete
else
super
end
end
# Duplicate internal structures when duplicating model instance.
def initialize_copy(other)
super
@instance_filters = other.send(:instance_filters).dup
self
end
# Lazily initialize the instance filter array.
def instance_filters
@instance_filters ||= []
end
# Apply the instance filters to the given dataset
def apply_instance_filters(ds)
instance_filters.inject(ds){|ds1, i| ds1.where(*i[0], &i[1])}
end
# Clear the instance filters.
def clear_instance_filters
instance_filters.clear
end
# Apply the instance filters to the dataset returned by super.
def _delete_dataset
apply_instance_filters(super)
end
# Apply the instance filters to the dataset returned by super.
def _update_dataset
apply_instance_filters(super)
end
# Only use prepared statements for update and delete queries
# if there are no instance filters.
def use_prepared_statements_for?(type)
if type == :update && !instance_filters.empty?
false
else
super if defined?(super)
end
end
end
end
end
end
|
