Added broken-object support.

Broken objects are objects who's class has gone away, typically
because modules or classes have been removed or moved.

src/ZODB/broken.py

+##############################################################################
+#
+# Copyright (c) 2004 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+"""Broken object support
+
+$Id: broken.py,v 1.1 2004/02/25 12:31:40 jim Exp $
+"""
+
+import sys
+import persistent
+
+broken_cache = {}
+
+class Broken(object):
+    """Broken object base class
+
+       Broken objects are placeholders for objects that can no longer be
+       created because their class has gone away.
+
+       Broken objects don't really do much of anything, except hold their
+       state.   The Broken class is used as a base class for creating
+       classes in leu of missing classes::
+
+         >>> Atall = type('Atall', (Broken, ), {'__module__': 'not.there'})
+
+       The only thing the class can be used for is to create new objects::
+
+         >>> Atall()
+         <broken not.there.Atall instance>
+         >>> Atall().__Broken_newargs__
+         ()
+         >>> Atall().__Broken_initargs__
+         ()
+
+         >>> Atall(1, 2).__Broken_newargs__
+         (1, 2)
+         >>> Atall(1, 2).__Broken_initargs__
+         (1, 2)
+
+         >>> a = Atall.__new__(Atall, 1, 2)
+         >>> a
+         <broken not.there.Atall instance>
+         >>> a.__Broken_newargs__
+         (1, 2)
+         >>> a.__Broken_initargs__
+
+       You can't modify broken objects::
+
+         >>> a.x = 1
+         Traceback (most recent call last):
+         ...
+         BrokenModified: Can't change broken objects
+
+       But you can set their state::
+
+         >>> a.__setstate__({'x': 1, })
+
+       You can pickle broken objects::
+
+         >>> r = a.__reduce__()
+         >>> len(r)
+         3
+         >>> r[0] is rebuild
+         True
+         >>> r[1]
+         ('not.there', 'Atall', 1, 2)
+         >>> r[2]
+         {'x': 1}
+
+         >>> import cPickle
+         >>> a2 = cPickle.loads(cPickle.dumps(a, 1))
+         >>> a2
+         <broken not.there.Atall instance>
+         >>> a2.__Broken_newargs__
+         (1, 2)
+         >>> a2.__Broken_initargs__
+         >>> a2.__Broken_state__
+         {'x': 1}
+
+       """
+
+    __Broken_state__ = __Broken_initargs__ = None
+
+    __name__ = 'bob XXX'
+
+    def __new__(class_, *args):
+        result = object.__new__(class_)
+        result.__dict__['__Broken_newargs__'] = args
+        return result
+
+    def __init__(self, *args):
+        self.__dict__['__Broken_initargs__'] = args
+
+    def __reduce__(self):
+        """We pickle broken objects in hope of being able to fix them later
+        """
+        return (rebuild,
+                ((self.__class__.__module__, self.__class__.__name__)
+                 + self.__Broken_newargs__),
+                self.__Broken_state__,
+                )
+
+    def __setstate__(self, state):
+        self.__dict__['__Broken_state__'] = state
+        
+    def __repr__(self):
+        return "<broken %s.%s instance>" % (
+            self.__class__.__module__, self.__class__.__name__)
+
+    def __setattr__(self, name, value):
+        raise BrokenModified("Can't change broken objects")
+
+def find_global(modulename, globalname, Broken=Broken):
+    """Find a global object, returninga broken class if it can't be found
+
+       This function looks up global variable in modules::
+
+         >>> import sys
+         >>> find_global('sys', 'path') is sys.path
+         True
+
+       If an object can't be found, a broken class is returned::
+
+         >>> broken = find_global('ZODB.not.there', 'atall')
+         >>> issubclass(broken, Broken)
+         True
+         >>> broken.__module__
+         'ZODB.not.there'
+         >>> broken.__name__
+         'atall'
+
+       Broken classes are cached::
+
+         >>> find_global('ZODB.not.there', 'atall') is broken
+         True
+
+       If we "repair" a missing global::
+
+         >>> class ZODBnotthere:
+         ...     atall = []
+
+         >>> sys.modules['ZODB.not'] = ZODBnotthere
+         >>> sys.modules['ZODB.not.there'] = ZODBnotthere
+
+       we can then get the repaired value::
+
+         >>> find_global('ZODB.not.there', 'atall') is ZODBnotthere.atall
+         True
+
+       Of course, if we beak it again::
+
+         >>> del sys.modules['ZODB.not']
+         >>> del sys.modules['ZODB.not.there']
+
+       we get the broken value::
+
+         >>> find_global('ZODB.not.there', 'atall') is broken
+         True
+
+       """
+    try:
+        __import__(modulename)
+    except ImportError:
+        pass
+    else:
+        module = sys.modules[modulename]
+        try:
+            return getattr(module, globalname)
+        except AttributeError:
+            pass
+
+    try:
+        return broken_cache[(modulename, globalname)]
+    except KeyError:
+        pass
+
+    class_ = type(globalname, (Broken, ), {'__module__': modulename})
+    broken_cache[(modulename, globalname)] = class_
+    return class_
+
+def rebuild(modulename, globalname, *args):
+    """Recreate a broken object, possibly recreating the missing class
+
+       This functions unpickles broken objects::
+
+         >>> broken = rebuild('ZODB.notthere', 'atall', 1, 2)
+         >>> broken
+         <broken ZODB.notthere.atall instance>
+         >>> broken.__Broken_newargs__
+         (1, 2)
+
+       If we "repair" the brokenness::
+
+         >>> class notthere: # fake notthere module
+         ...     class atall(object):
+         ...         def __new__(self, *args):
+         ...             ob = object.__new__(self)
+         ...             ob.args = args
+         ...             return ob
+         ...         def __repr__(self):
+         ...             return 'atall %s %s' % self.args
+
+         >>> sys.modules['ZODB.notthere'] = notthere
+
+         >>> rebuild('ZODB.notthere', 'atall', 1, 2)
+         atall 1 2
+
+         >>> del sys.modules['ZODB.notthere']
+
+       """
+    class_ = find_global(modulename, globalname)
+    return class_.__new__(class_, *args)
+        
+class BrokenModified(TypeError):
+    """Attempt to modify a broken object
+    """
+
+class PersistentBroken(Broken, persistent.Persistent):
+    r"""Persistent broken objects
+
+        Persistent broken objects are used for broken objects that are
+        also persistent.  In addition to having to track the original
+        object data, they need to handle persistent meta data.
+
+        Persistent broken classes are created from existing broken classes
+        using the persistentBroken, function::
+
+          >>> Atall = type('Atall', (Broken, ), {'__module__': 'not.there'})
+          >>> PAtall = persistentBroken(Atall)
+
+        (Note that we always get the *same* persistent broken class
+         for a given broken class::
+
+          >>> persistentBroken(Atall) is PAtall
+          True
+          
+         )
+
+        Persistent broken classes work a lot like broken classes::
+
+          >>> a = PAtall.__new__(PAtall, 1, 2)
+          >>> a
+          <persistent broken not.there.Atall instance None>
+          >>> a.__Broken_newargs__
+          (1, 2)
+          >>> a.__Broken_initargs__
+          >>> a.x = 1
+          Traceback (most recent call last):
+          ...
+          BrokenModified: Can't change broken objects
+
+        Unlike regular broken objects, persistent broken objects keep
+        track of persistence meta data:
+
+          >>> a._p_oid = '\0\0\0\0****'
+          >>> a
+          <persistent broken not.there.Atall instance '\x00\x00\x00\x00****'>
+
+        and persistent broken objects aren't directly picklable:
+
+          >>> a.__reduce__()
+          Traceback (most recent call last):
+          ...
+          BrokenModified: """ \
+        r"""<persistent broken not.there.Atall instance '\x00\x00\x00\x00****'>
+
+        but you can get their state:
+
+          >>> a.__setstate__({'y': 2})
+          >>> a.__getstate__()
+          {'y': 2}
+
+        """
+
+    def __new__(class_, *args):
+        result = persistent.Persistent.__new__(class_)
+        result.__dict__['__Broken_newargs__'] = args
+        return result
+
+    def __reduce__(self, *args):
+        raise BrokenModified(self)
+
+    def __getstate__(self):
+        return self.__Broken_state__
+
+    def __setattr__(self, name, value):
+        if name.startswith('_p_'):
+            persistent.Persistent.__setattr__(self, name, value)
+        else:
+            raise BrokenModified("Can't change broken objects")
+        
+    def __repr__(self):
+        return "<persistent broken %s.%s instance %r>" % (
+            self.__class__.__module__, self.__class__.__name__,
+            self._p_oid)
+
+    def __getnewargs__(self):
+        return self.__Broken_newargs__
+
+def persistentBroken(class_):
+    try:
+        return class_.__dict__['__Broken_Persistent__']
+    except KeyError:
+        class_.__Broken_Persistent__ = (
+            type(class_.__name__,
+                 (PersistentBroken, class_),
+                 {'__module__': class_.__module__},
+                 )
+            )
+        return class_.__dict__['__Broken_Persistent__']

src/ZODB/serialize.py

@@ -86,14 +86,16 @@ import cPickle
 import cStringIO
 import logging
 
+
 from persistent import Persistent
 from persistent.wref import WeakRefMarker, WeakRef
+from ZODB import broken
+from ZODB.broken import Broken
 from ZODB.POSException import InvalidObjectReference
 
-# Might to update or redo to reflect weakrefs
+# Might to update or redo coptimizations to reflect weakrefs:
 # from ZODB.coptimizations import new_persistent_id
 
-
 def myhasattr(obj, name, _marker=object()):
     """Make sure we don't mask exceptions like hasattr().
 
@@ -369,13 +371,20 @@ class BaseObjectReader:
             if isinstance(klass, tuple):
                 # Old module_name, class_name tuple
                 klass = self._get_class(*klass)
+
             if args is None:
-                return klass.__new__(klass)
-            else:
-                return klass.__new__(klass, *args)
+                args = ()
         else:
             # Definately new style direct class reference
-            return klass.__new__(klass)
+            args = ()
+
+        if issubclass(klass, Broken):
+            # We got a broken class. We might need to make it
+            # PersistentBroken
+            if not issubclass(klass, broken.PersistentBroken):
+                klass = broken.persistentBroken(klass)
+
+        return klass.__new__(klass, *args)
 
     def getState(self, pickle):
         unpickler = self._get_unpickler(pickle)
@@ -420,16 +429,37 @@ class ConnectionObjectReader(BaseObjectReader):
     def _get_class(self, module, name):
         return self._factory(self._conn, module, name)
 
+    def _get_unpickler(self, pickle):
+        unpickler = BaseObjectReader._get_unpickler(self, pickle)
+        factory = self._factory
+        conn = self._conn
+
+        def find_global(modulename, name):
+            return factory(conn, modulename, name)
+
+        unpickler.find_global = find_global
+
+        return unpickler
+
     def _persistent_load(self, oid):
         if isinstance(oid, tuple):
             # Quick instance reference.  We know all we need to know
             # to create the instance w/o hitting the db, so go for it!
             oid, klass = oid
+
             obj = self._cache.get(oid, None) # XXX it's not a dict
             if obj is not None:
                 return obj
+
             if isinstance(klass, tuple):
                 klass = self._get_class(*klass)
+
+            if issubclass(klass, Broken):
+                # We got a broken class. We might need to make it
+                # PersistentBroken
+                if not issubclass(klass, broken.PersistentBroken):
+                    klass = broken.persistentBroken(klass)
+
             try:
                 obj = klass.__new__(klass)
             except TypeError:

src/ZODB/tests/testBroken.py

+##############################################################################
+#
+# Copyright (c) 2004 Zope Corporation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.0 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+"""Test broken-object suppport
+
+$Id: testBroken.py,v 1.1 2004/02/25 12:31:41 jim Exp $
+"""
+
+import sys
+import unittest
+import persistent
+from transaction import get_transaction
+from doctest import DocTestSuite
+from ZODB.tests.util import DB
+
+def test_integration():
+    """Test the integration of broken object support with the databse:
+
+    >>> db = DB()
+
+    We'll create a fake module with a class:
+    
+    >>> class NotThere:
+    ...     Atall = type('Atall', (persistent.Persistent, ),
+    ...                  {'__module__': 'ZODB.not.there'})
+
+    And stuff this into sys.modules to simulate a regular module:
+
+    >>> sys.modules['ZODB.not.there'] = NotThere
+    >>> sys.modules['ZODB.not'] = NotThere
+
+    Now, we'll create and save an instance, and make sure we can
+    load it in another connection:
+
+    >>> a = NotThere.Atall()
+    >>> a.x = 1
+    >>> conn1 = db.open()
+    >>> conn1.root()['a'] = a
+    >>> get_transaction().commit()
+
+    >>> conn2 = db.open()
+    >>> a2 = conn2.root()['a']
+    >>> a2.__class__ is a.__class__
+    True
+    >>> a2.x
+    1
+
+    Now, we'll uninstall the module, simulating having the module
+    go away:
+
+    >>> del sys.modules['ZODB.not.there']
+
+    and we'll try to load the object in another connection:
+
+    >>> conn3 = db.open()
+    >>> a3 = conn3.root()['a']
+    >>> a3
+    <persistent broken ZODB.not.there.Atall instance """ \
+       r"""'\x00\x00\x00\x00\x00\x00\x00\x01'>
+
+    >>> a3.__Broken_state__
+    {'x': 1}
+    
+
+    >>> db.close()
+    """
+
+def test_suite():
+    return unittest.TestSuite((
+        DocTestSuite('ZODB.broken'),
+        DocTestSuite(),
+        ))
+
+if __name__ == '__main__': unittest.main()