Added a database-backed cache backend, along with a tool in django-admin to

create the necessary table structure.  This closes #515; thanks again, 
Eugene!


git-svn-id: http://code.djangoproject.com/svn/django/trunk@692 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/bin/django-admin.py

@@ -6,6 +6,7 @@ import os, sys
 ACTION_MAPPING = {
     'adminindex': management.get_admin_index,
     'createsuperuser': management.createsuperuser,
+    'createcachetable' : management.createcachetable,
 #     'dbcheck': management.database_check,
     'init': management.init,
     'inspectdb': management.inspectdb,
@@ -23,7 +24,7 @@ ACTION_MAPPING = {
     'validate': management.validate,
 }
 
-NO_SQL_TRANSACTION = ('adminindex', 'dbcheck', 'install', 'sqlindexes')
+NO_SQL_TRANSACTION = ('adminindex', 'createcachetable', 'dbcheck', 'install', 'sqlindexes')
 
 def get_usage():
     """
@@ -79,6 +80,11 @@ def main():
         except NotImplementedError:
             sys.stderr.write("Error: %r isn't supported for the currently selected database backend.\n" % action)
             sys.exit(1)
+    elif action == 'createcachetable':
+        try:
+            ACTION_MAPPING[action](args[1])
+        except IndexError:
+            parser.print_usage_and_exit()
     elif action in ('startapp', 'startproject'):
         try:
             name = args[1]

django/core/cache.py

@@ -15,10 +15,9 @@ The CACHE_BACKEND setting is a quasi-URI; examples are:
     memcached://127.0.0.1:11211/    A memcached backend; the server is running
                                     on localhost port 11211.
 
-    sql://tablename/                A SQL backend.  If you use this backend,
+    db://tablename/                 A database backend in a table named 
-                                    you must have django.contrib.cache in
+                                    "tablename". This table should be created
-                                    INSTALLED_APPS, and you must have installed
+                                    with "django-admin createcachetable".
-                                    the tables for django.contrib.cache.
 
     file:///var/tmp/django_cache/   A file-based cache stored in the directory
                                     /var/tmp/django_cache/.
@@ -55,7 +54,7 @@ arguments are:
 For example:
 
     memcached://127.0.0.1:11211/?timeout=60
-    sql://tablename/?timeout=120&max_entries=500&cull_percentage=4
+    db://tablename/?timeout=120&max_entries=500&cull_percentage=4
 
 Invalid arguments are silently ignored, as are invalid values of known
 arguments.
@@ -351,6 +350,83 @@ class _FileCache(_SimpleCache):
     def _key_to_file(self, key):
         return os.path.join(self._dir, urllib.quote_plus(key))
 
+#############
+# SQL cache #
+#############
+
+import base64
+from django.core.db import db
+from datetime import datetime
+
+class _DBCache(_Cache):
+    """SQL cache backend"""
+    
+    def __init__(self, table, params):
+        _Cache.__init__(self, params)
+        self._table = table
+        max_entries = params.get('max_entries', 300) 
+        try: 
+            self._max_entries = int(max_entries) 
+        except (ValueError, TypeError): 
+            self._max_entries = 300 
+        cull_frequency = params.get('cull_frequency', 3) 
+        try: 
+            self._cull_frequency = int(cull_frequency) 
+        except (ValueError, TypeError): 
+            self._cull_frequency = 3 
+        
+    def get(self, key, default=None):
+        cursor = db.cursor()
+        cursor.execute("SELECT key, value, expires FROM %s WHERE key = %%s" % self._table, [key])
+        row = cursor.fetchone()
+        if row is None:
+            return default
+        now = datetime.now()
+        if row[2] < now:
+            cursor.execute("DELETE FROM %s WHERE key = %%s" % self._table, [key])
+            db.commit()
+            return default
+        return pickle.loads(base64.decodestring(row[1]))
+        
+    def set(self, key, value, timeout=None):
+        if timeout is None:
+            timeout = self.default_timeout
+        cursor = db.cursor()
+        cursor.execute("SELECT COUNT(*) FROM %s" % self._table)
+        num = cursor.fetchone()[0]
+        now = datetime.now().replace(microsecond=0)
+        exp = datetime.fromtimestamp(time.time() + timeout).replace(microsecond=0)
+        if num > self._max_entries:
+            self._cull(cursor, now)
+        encoded = base64.encodestring(pickle.dumps(value, 2)).strip()
+        cursor.execute("SELECT key FROM %s WHERE key = %%s" % self._table, [key])
+        if cursor.fetchone():
+            cursor.execute("UPDATE %s SET value = %%s, expires = %%s WHERE key = %%s" % self._table, [encoded, str(exp), key])
+        else:
+            cursor.execute("INSERT INTO %s (key, value, expires) VALUES (%%s, %%s, %%s)" % self._table, [key, encoded, str(exp)])
+        db.commit()
+        
+    def delete(self, key):
+        cursor = db.cursor()
+        cursor.execute("DELETE FROM %s WHERE key = %%s" % self._table, [key])
+        db.commit()
+        
+    def has_key(self, key):
+        cursor = db.cursor()
+        cursor.execute("SELECT key FROM %s WHERE key = %%s" % self._table, [key])
+        return cursor.fetchone() is not None
+        
+    def _cull(self, cursor, now):
+        if self._cull_frequency == 0:
+            cursor.execute("DELETE FROM %s" % self._table)
+        else:
+            cursor.execute("DELETE FROM %s WHERE expires < %%s" % self._table, [str(now)])
+            cursor.execute("SELECT COUNT(*) FROM %s" % self._table)
+            num = cursor.fetchone()[0]
+            if num > self._max_entries:
+                cursor.execute("SELECT key FROM %s ORDER BY key LIMIT 1 OFFSET %%s" % self._table, [num / self._cull_frequency])
+                cursor.execute("DELETE FROM %s WHERE key < %%s" % self._table, [cursor.fetchone()[0]])
+        
 ##########################################
 # Read settings and load a cache backend #
 ##########################################
@@ -362,6 +438,7 @@ _BACKENDS = {
     'simple'    : _SimpleCache,
     'locmem'    : _LocMemCache,
     'file'      : _FileCache,
+    'db'        : _DBCache,
 }
 
 def get_cache(backend_uri):

django/core/management.py

@@ -621,3 +621,35 @@ def runserver(addr, port):
     from django.utils import autoreload
     autoreload.main(inner_run)
 runserver.args = '[optional port number, or ipaddr:port]'
+
+def createcachetable(tablename):
+    "Creates the table needed to use the SQL cache backend"
+    from django.core import db, meta
+    fields = (
+        meta.CharField(name='key', maxlength=255, unique=True, primary_key=True),
+        meta.TextField(name='value'),
+        meta.DateTimeField(name='expires', db_index=True),
+    )
+    table_output = []
+    index_output = []
+    for f in fields:
+        field_output = [f.column, db.DATA_TYPES[f.__class__.__name__] % f.__dict__]
+        field_output.append("%sNULL" % (not f.null and "NOT " or ""))
+        if f.unique:
+            field_output.append("UNIQUE")
+        if f.primary_key:
+            field_output.append("PRIMARY KEY")
+        if f.db_index:
+            unique = f.unique and "UNIQUE " or ""
+            index_output.append("CREATE %sINDEX %s_%s ON %s (%s);" % (unique, tablename, f.column, tablename, f.column))
+        table_output.append(" ".join(field_output))
+    full_statement = ["CREATE TABLE %s (" % tablename]
+    for i, line in enumerate(table_output):
+        full_statement.append('    %s%s' % (line, i < len(table_output)-1 and ',' or ''))
+    full_statement.append(');')
+    curs = db.db.cursor()
+    curs.execute("\n".join(full_statement))
+    for statement in index_output:
+        curs.execute(statement)
+    db.db.commit()
+createcachetable.args = "[tablename]"

docs/cache.txt

@@ -29,10 +29,20 @@ Examples:
     memcached://127.0.0.1:11211/    A memcached backend; the server is running
                                     on localhost port 11211.
 
+    db://tablename/                 A database backend in a table named 
+                                    "tablename". This table should be created
+                                    with "django-admin createcachetable".
+
+    file:///var/tmp/django_cache/   A file-based cache stored in the directory
+                                    /var/tmp/django_cache/.
+
     simple:///                      A simple single-process memory cache; you
                                     probably don't want to use this except for
                                     testing. Note that this cache backend is
                                     NOT threadsafe!
+                                        
+    locmem:///                      A more sophisticaed local memory cache;
+                                    this is multi-process- and thread-safe.
     ==============================  ===========================================
 
 All caches may take arguments -- they're given in query-string style.  Valid

docs/django-admin.txt

@@ -40,6 +40,14 @@ your admin's index page. See `Tutorial 2`_ for more information.
 
 .. _Tutorial 2: http://www.djangoproject.com/documentation/tutorial2/
 
+createcachetable [tablename]
+----------------------------
+
+Creates a cache table named ``tablename`` for use with the database cache
+backend.  See the `cache documentation`_ for more information.
+
+.. _cache documentation: http://www.djangoproject.com/documentation/cache/
+
 createsuperuser
 ---------------