Question

I am trying to persist a large class called an Authorizer which holds a reference to a database connection and a container of other objects representing the result of a complicated set of database queries. I want to serialize the expensive to build parts of this object in a session. Then when I need to ask the Authorizer a question I want to wake the Authorizer object up instead of building a new one for each page. I am writing a custom handler to temporarily store this object in a database table. I understand that the magic method __sleep() is usually used to handle choosing which parts of the object to store and then __wakeup() is used to restore the database connection.

This is where I get fuzzy. I think serialize() and unserialize() are supposed to work instead of the constructor and destructor, but I can’t quite understand how they interact with __sleep() and __wakeup(). Then I got to the part of the manual describing the serializable interface and thought OK I will be able to implement this and be sure I have this right. Then I read that classes which implement this interface no longer support __sleep() and __wakeup()! That was the only part of this whole thing I really understood >:-{ I couldn’t find any examples at all of how to properly implement this interface.

So my question is what is the preferred way to implement serialization in a completely object oriented system? Is the serializable interface meant to replace an older method? What is the purpose of having two different sets of functions (_sleep()/_wakeup() and serialize()/unserialize())?

Answer 1

__sleep and __wakeup are called by the default serialize/unserialize methods to prepare the object for serialization. This works in the case where the default PHP method does close to what you need and you simply need to perform some cleanup around the process.

If you’re implementing the Serializable interface, then there’s no need for these methods are you’re declaring that you are implementing the entirety of the serialization process yourself. So any work which would normally be done in __sleep would be incorporated into serialize, and the same with __wakeup and unserialize.