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module Moneta
# Provides a fallback to a second store when an exception is raised
#
# @example Basic usage - catches any {IOError} and falls back to {Moneta::Adapters:Null}
# Moneta.build do
# use :Fallback
# adapter :Client
# end
#
# @example Specifying an exception to rescue
# Moneta.build do
# use :Fallback, rescue: Redis::CannotConnectError
# adapter :Redis
# end
#
# @example Specifying a different fallback
# Moneta.build do
# use :Fallback do
# # This is a new builder context
# adapter :Memory
# end
# adapter :File, dir: 'cache'
# end
#
# @api public
class Fallback < Wrapper
# @param [Moneta store] adapter The underlying store
# @param [Hash] options
# @option options [Moneta store] :fallback (:Null store) The store to fall
# back on
# @option options [Class|Array<Class>] :rescue ([IOError]) The list
# of exceptions that should be rescued
# @yieldreturn [Moneta store] Moneta store built using the builder API
def initialize(adapter, options = {}, &block)
super
@fallback =
if block_given?
::Moneta.build(&block)
elsif options.key?(:fallback)
options.delete(:fallback)
else
::Moneta::Adapters::Null.new
end
@rescue =
case options[:rescue]
when nil
[::IOError]
when Array
options[:rescue]
else
[options[:rescue]]
end
end
protected
def wrap(name, *args, &block)
yield
rescue => e
raise unless @rescue.any? { |rescuable| rescuable === e }
fallback(name, *args, &block)
end
def fallback(name, *args, &block)
result =
case name
when :values_at, :fetch_values, :slice
keys, options = args
@fallback.public_send(name, *keys, **options, &block)
else
@fallback.public_send(name, *args, &block)
end
# Don't expose the fallback class to the caller
if result == @fallback
self
else
result
end
end
end
end
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