Generally when trying to store objects in the session, in files or pass them through sockets, the object can be referenced as being of the __PHP_Incomplete_Class class, this is because the correct way to store and retrieve an object in session and also in other cases) is to use the functions serialize() and unserialize() .

Note: It is interesting to note that in many cases (with the%% flag disabled in session.auto_start ), it is necessary to include the definition of the class before the call to the function php.ini .

In addition to the above, it is important to remember that PHP returns a __php_incomplete_class instance when you call the unserialize function on a string that contains a serialization of a class that does not exist in the current context.

For example:

• Create class X
• Serialize its instance with serialize(new X) .
• Copy the result of it to string . is something like O:1:"X":0:{} .
• Delete the class X .
• Call unserialize('O:1:"X":0:{}') , without class X being declared.

PHP will return the following:

object(__PHP_Incomplete_Class)#198 (1) {
  ["__PHP_Incomplete_Class_Name"]=>
  string(1) "X"
}

With class class X {} being declared in the document that used unserialize , this would be returned:

object(X)#202 (0) {
}

Care

You should take care when saving certain types of data in session. For example, suppose you saved the user information logged in through an object:

$_SESSION['usuario'] = Usuario::find(1); // retorna uma instância de Usuario

If for some reason, because of a maintenance, you have changed the name of the class Usuario to UsuarioSite , for example, the user who has the saved session, before updating your maintenance, will have problems with the __php_incomplete_class , due to non existence of the reference (class) Usuario .