Provide a simple example of using dbm files ad ZODB storages.

src/ZODB/dbmStorage.py

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+# This software consists of contributions made by Digital Creations and
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+##############################################################################
+"""Very Simple dbm-based ZODB storage
+
+This storage provides for use of dbm files as storages that
+don't support versions or Undo.  This may be useful when implementing
+objects like hit counters that don't need or want to participate
+in undo or versions.
+"""
+__version__='$Revision: 1.1 $'[11:-2]
+
+import base64, POSException, time, string, utils
+
+from MappingStorage import MappingStorage
+from BaseStorage import BaseStorage
+import anydbm, os
+
+class anydbmStorage(MappingStorage):
+
+    def __init__(self, filename, flag='r', mode=0666):
+
+
+        BaseStorage.__init__(self, filename)
+        self._index=anydbm.open(filename, flag, mode)
+        self._tindex=[]
+        keys=self._index.keys()
+        if keys: self._oid=max(keys)
+
+    def getSize(self):
+        # This is a little iffy, since we aren't entirely sure what the file is
+        self._lock_acquire()
+        try:    
+            try:
+                return (os.stat(self.__name__+'.data')[6] +
+                        os.stat(self.__name__+'.dir')[6]
+                        )
+            except:
+                try: return os.stat(self.__name__)[6]
+                except: return 0
+        finally: self._lock_release()
+
+class gdbmStorage(anydbmStorage):
+
+    def __init__(self, filename, flag='r', mode=0666):
+
+        BaseStorage.__init__(self, filename)
+        import gdbm
+        self._index=index=gdbm.open(filename, flag[:1]+'f', mode)
+        self._tindex=[]
+
+        m='\0\0\0\0\0\0\0\0'
+        oid=index.firstkey()
+        while oid != None:
+            m=max(m, oid)
+            oid=index.nextkey(oid)
+
+        self._oid=m
+
+    def getSize(self):
+        self._lock_acquire()
+        try: return os.stat(self.__name__)[6]
+        finally: self._lock_release()
+
+    def pack(self, t, referencesf):
+        
+        self._lock_acquire()
+        try:    
+            # Build an index of *only* those objects reachable
+            # from the root.
+            index=self._index
+            rootl=['\0\0\0\0\0\0\0\0']
+            pop=rootl.pop
+            pindex={}
+            referenced=pindex.has_key
+            while rootl:
+                oid=pop()
+                if referenced(oid): continue
+    
+                # Scan non-version pickle for references
+                r=index[oid]
+                pindex[oid]=r
+                p=r[8:]
+                referencesf(p, rootl)
+
+            # Now delete any unreferenced entries:
+
+            deleted=[]
+            oid=index.firstkey()
+            while oid != None:
+                if not referenced(oid): deleted.append(oid)
+                oid=index.nextkey(oid)
+
+            pindex=referenced=None
+
+            for oid in deleted: del index[oid]
+
+            index.sync()
+            index.reorganize()
+    
+        finally: self._lock_release()
+
+
+    def _finish(self, tid, user, desc, ext):
+
+        index=self._index
+        for oid, p in self._tindex: index[oid]=p
+        index.sync()