Make pure-python Persistent only call jar.setstate() when it is a ghost instead of every time.

CHANGES.rst

@@ -4,6 +4,11 @@
 4.0.8 (Unreleased)
 ------------------
 
+- In pure-Python ``Persistent``, calling ``_p_activate`` no longer
+  corrupts the state of a non-ghost object, and it doesn't throw
+  ``POSKeyError`` if called on an object that has never been committed.
+  (PR #9)
+
 - In pure-Python ``Persistent``, avoid calling a subclass's ``__setattr__``
   at instance creation time. (PR #8)
 

persistent/persistence.py

@@ -330,14 +330,14 @@ class Persistent(object):
         """ See IPersistent.
         """
         before = self.__flags
-        if self.__flags is None:
+        if self.__flags is None or self._p_state < 0: # Only do this if we're a ghost
             self.__flags = 0
-        if self.__jar is not None and self.__oid is not None:
-            try:
-                self.__jar.setstate(self)
-            except:
-                self.__flags = before
-                raise
+            if self.__jar is not None and self.__oid is not None:
+                try:
+                    self.__jar.setstate(self)
+                except:
+                    self.__flags = before
+                    raise
 
     def _p_deactivate(self):
         """ See IPersistent.

persistent/tests/test_persistence.py

@@ -978,6 +978,19 @@ class _Persistent_Base(object):
         inst._p_activate() # noop from 'saved' state
         self.assertEqual(inst._p_status, 'saved')
 
+    def test__p_activate_only_sets_state_once(self):
+        inst, jar, OID = self._makeOneWithJar()
+        # No matter how many times we call _p_activate, it
+        # only sets state once, the first time
+        inst._p_invalidate() # make it a ghost
+        self.assertEqual(list(jar._loaded), [])
+
+        inst._p_activate()
+        self.assertEqual(list(jar._loaded), [OID])
+
+        inst._p_activate()
+        self.assertEqual(list(jar._loaded), [OID])
+
     def test__p_deactivate_from_unsaved(self):
         inst = self._makeOne()
         inst._p_deactivate()