关于异常：Ruby自定义错误类：message属性的继承

Ruby custom error classes: inheritance of the message attribute

我似乎找不到关于自定义异常类的很多信息。

我所知道的

您可以声明您的自定义错误类并让它从StandardError继承，所以它可以是rescued：

1 2	class MyCustomError < StandardError end

这允许您使用以下方法提升它：

1	raise MyCustomError,"A message"

稍后，在救援时得到这个信息

1 2	rescue MyCustomError => e puts e.message # =>"A message"

我不知道的

我想给我的异常一些自定义字段，但我想从父类继承message属性。我在阅读这个主题时发现，@message不是异常类的实例变量，所以我担心我的继承将不起作用。

有人能告诉我更多细节吗？如何使用object属性实现自定义错误类？以下是否正确：

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class MyCustomError < StandardError
attr_reader :object
def initialize(message, object)
super(message)
@object = object
end
end

然后：

1	raise MyCustomError.new(anObject),"A message"

得到：

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rescue MyCustomError => e
puts e.message # =>"A message"
puts e.object # => anObject

它能工作吗？如果能，这是正确的做事方式吗？

相关讨论

考虑到Exception的Ruby核心文档(所有其他错误都是从该文档继承的)所描述的关于#message的内容。

Returns the result of invoking exception.to_s. Normally this returns
the exception’s message or name. By supplying a to_str method,
exceptions are agreeing to be used where Strings are expected.

http://ruby doc.org/core-1.9.3/exception.html method-i-message

我会选择重新定义to_s/to_str或初始值设定项。下面是一个例子，我们希望以一种大多数人都能读懂的方式，知道当一个外部服务未能完成某些事情时。

注意：下面的第二个策略使用rails-pretty-string方法，例如demodualize，这可能有点复杂，因此在异常情况下可能不明智。如果需要，还可以向方法签名添加更多参数。

凌驾于战略之上，而不是凌驾于战略之上，它的工作方式不同

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module ExternalService

class FailedCRUDError < ::StandardError
def to_s
'failed to crud with external service'
end
end

class FailedToCreateError < FailedCRUDError; end
class FailedToReadError < FailedCRUDError; end
class FailedToUpdateError < FailedCRUDError; end
class FailedToDeleteError < FailedCRUDError; end
end

控制台输出

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begin; raise ExternalService::FailedToCreateError; rescue => e; e.message; end
# =>"failed to crud with external service"

begin; raise ExternalService::FailedToCreateError, 'custom message'; rescue => e; e.message; end
# =>"failed to crud with external service"

begin; raise ExternalService::FailedToCreateError.new('custom message'); rescue => e; e.message; end
# =>"failed to crud with external service"

raise ExternalService::FailedToCreateError
# ExternalService::FailedToCreateError: failed to crud with external service

重写初始化策略

这是最接近我在Rails中使用的实现的策略。如上所述，它使用demodualize、underscore和humanizeActiveSupport方法。但这可以很容易地消除，就像以前的策略一样。

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module ExternalService
class FailedCRUDError < ::StandardError
def initialize(service_model=nil)
super("#{self.class.name.demodulize.underscore.humanize} using #{service_model.class}")
end
end

class FailedToCreateError < FailedCRUDError; end
class FailedToReadError < FailedCRUDError; end
class FailedToUpdateError < FailedCRUDError; end
class FailedToDeleteError < FailedCRUDError; end
end

控制台输出

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begin; raise ExternalService::FailedToCreateError; rescue => e; e.message; end
# =>"Failed to create error using NilClass"

begin; raise ExternalService::FailedToCreateError, Object.new; rescue => e; e.message; end
# =>"Failed to create error using Object"

begin; raise ExternalService::FailedToCreateError.new(Object.new); rescue => e; e.message; end
# =>"Failed to create error using Object"

raise ExternalService::FailedCRUDError
# ExternalService::FailedCRUDError: Failed crud error using NilClass

raise ExternalService::FailedCRUDError.new(Object.new)
# RuntimeError: ExternalService::FailedCRUDError using Object

演示工具

这是一个演示，演示上述实现的救援和消息传递。引发异常的类是对Cloudinary的一个伪API。只需将上述策略之一转储到Rails控制台中，然后执行此操作。

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require 'rails' # only needed for second strategy

module ExternalService
class FailedCRUDError < ::StandardError
def initialize(service_model=nil)
@service_model = service_model
super("#{self.class.name.demodulize.underscore.humanize} using #{@service_model.class}")
end
end

class FailedToCreateError < FailedCRUDError; end
class FailedToReadError < FailedCRUDError; end
class FailedToUpdateError < FailedCRUDError; end
class FailedToDeleteError < FailedCRUDError; end
end

# Stub service representing 3rd party cloud storage
class Cloudinary

def initialize(*error_args)
@error_args = error_args.flatten
end

def create_read_update_or_delete
begin
try_and_fail
rescue ExternalService::FailedCRUDError => e
e.message
end
end

private def try_and_fail
raise *@error_args
end
end

errors_map = [
# Without an arg
ExternalService::FailedCRUDError,
ExternalService::FailedToCreateError,
ExternalService::FailedToReadError,
ExternalService::FailedToUpdateError,
ExternalService::FailedToDeleteError,
# Instantiated without an arg
ExternalService::FailedCRUDError.new,
ExternalService::FailedToCreateError.new,
ExternalService::FailedToReadError.new,
ExternalService::FailedToUpdateError.new,
ExternalService::FailedToDeleteError.new,
# With an arg
[ExternalService::FailedCRUDError, Object.new],
[ExternalService::FailedToCreateError, Object.new],
[ExternalService::FailedToReadError, Object.new],
[ExternalService::FailedToUpdateError, Object.new],
[ExternalService::FailedToDeleteError, Object.new],
# Instantiated with an arg
ExternalService::FailedCRUDError.new(Object.new),
ExternalService::FailedToCreateError.new(Object.new),
ExternalService::FailedToReadError.new(Object.new),
ExternalService::FailedToUpdateError.new(Object.new),
ExternalService::FailedToDeleteError.new(Object.new),
].inject({}) do |errors, args|
begin
errors.merge!( args => Cloudinary.new(args).create_read_update_or_delete)
rescue => e
binding.pry
end
end

if defined?(pp) || require('pp')
pp errors_map
else
errors_map.each{ |set| puts set.inspect }
end

你的想法是对的，但你称之为错误的方式。应该是

1	raise MyCustomError.new(an_object,"A message")