如何将对象转换为字符串以用于ActiveRecord查询？ [英] How can I cast an object to string for use with ActiveRecord queries?
问题描述
我有一个用户，其中有一个 String 电子邮件属性。但是，当我在应用程序中处理电子邮件时，我发现最好先将其转换为（非持久性） Email 对象，如下所示：
I have a User, which has a String email attribute. However, when I'm dealing with an email in my app, I find it desirable to first convert it to a (non-persisted) Email object, like so:
class User < ActiveRecord::Base
def email
Email.new(self.read_attribute :email)
end
end
Email＃to_s 和 Email＃to_str 都被定义为只能是原始字符串（例如， foo@bar.com ），因此对于客户来说，无论他们是否处理电子邮件，它通常都是相当透明的或 String 。
Email#to_s and Email#to_str are both defined to be simply the original string (e.g., foo@bar.com), so it's usually pretty transparent to the client whether they're dealing with an Email or a String.
这在使用 ActiveRecord 分配属性时非常有效：
This works perfectly when assigning attributes with ActiveRecord:
> email = Email.new('foo@bar.com')
> user.email = email
ActiveRecord知道电子邮件属性是一个字符串，并相应地转换 Email 对象。令人费解的是，查询数据库时不会执行此操作：
ActiveRecord knows that the email attribute is a string and converts the Email object accordingly. Somewhat puzzlingly, it doesn't do this when querying the database:
> email = Email.new('foo@bar.com')
> User.find_by email: email
ActiveRecord::StatementInvalid: can't cast Email to string
显然，我可以打电话给
> User.find_by email: email.to_s
但是有没有办法使这种转换自动发生？ / p>
But is there a way to make this cast happen automatically?
推荐答案
这是负责任的对象，用于将对象强制转换为ActiveModel中的字符串。看看 serialize 方法：没有处理电子邮件的情况。
This is the responsible object for casting an object to a string in ActiveModel. Take a look at the serialize method there: it doesn't have a case for handling Email.
您可以添加一个通过扩展类：
You can add one by extending the class:
module EmailSupport
def serialize(value)
case value
when Email then value.to_s
else super
end
end
end
ActiveModel::Type::ImmutableString.include(EmailSupport)
User.find_by email: Email.new('foo@example.org')
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