Ruby-on-rails 如何从Rails中的名称字符串实例化类？
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How to instantiate class from name string in Rails?
提问by Vjatseslav Gedrovits
How we can instantiate class from it's name string in Ruby-on-Rails?
我们如何从 Ruby-on-Rails 中的名称字符串实例化类？
For example we have it's name in database in format like "ClassName" or "my_super_class_name".
例如，我们在数据库中以“ClassName”或“my_super_class_name”等格式存储它的名称。
How we can create object from it?
我们如何从中创建对象？
Solution:
解决方案：
Was looking for it myself, but not found, so here it is. Ruby-on-Rails API Method
自己也在找，没找到，所以来了。 Ruby-on-Rails API 方法
name = "ClassName"
instance = name.constantize.new
It can be even not formatted, we can user string method .classify
它甚至可以不格式化，我们可以使用字符串方法.classify
name = "my_super_class"
instance = name.classify.constantize.new
Of course maybe this is not very 'Rails way', but it solves it's purpose.
当然，也许这不是“Rails 方式”，但它解决了它的目的。
回答by Eugene Rourke
klass = Object.const_get "ClassName"
about class methods
关于类方法
class KlassExample
def self.klass_method
puts "Hello World from Class method"
end
end
klass = Object.const_get "KlassExample"
klass.klass_method
irb(main):061:0> klass.klass_method
Hello World from Class method
回答by maninalift
Others may also be looking for an alternative that does not throw an error if it fails to find the class. safe_constantizeis just that.
其他人也可能正在寻找一种替代方法，如果无法找到类，则不会抛出错误。safe_constantize就是这样。
class MyClass
end
"my_class".classify.safe_constantize.new # #<MyClass:0x007fec3a96b8a0>
"omg_evil".classify.safe_constantize.new # nil
回答by Pushp Raj Saurabh
You can simply convert a string and initialize a class out of it by:
您可以简单地转换一个字符串并通过以下方式初始化一个类：
klass_name = "Module::ClassName"
klass_name.constantize
To initialize a new object:
初始化一个新对象：
klass_name.constantize.new
I hope this turns out to be helpful. Thanks!
我希望这会有所帮助。谢谢！
回答by RubesMN
I'm surprised nobody is considering security and hacking in their responses. Instantiation of an arbitrary string that likely came even indirectly from user input is asking for trouble and hacking. We all should/must be whitelisting unless we're sure the string is fully controlled and monitored
我很惊讶没有人在他们的回复中考虑安全性和黑客攻击。甚至可能间接来自用户输入的任意字符串的实例化是自找麻烦和黑客攻击。我们都应该/必须加入白名单，除非我们确定字符串是完全控制和监控的
def class_for(name)
{
"foo" => Foo,
"bar" => Bar,
}[name] || raise UnknownClass
end
class_for(name_wherever_this_came_from).create!(params_somehow)
How you would know the appropriate params arbitrarily without having a whitelist would be challenging but you get the idea.
如何在没有白名单的情况下任意知道适当的参数将具有挑战性，但您明白了。
