diff -r 000000000000 -r 0d40e90630ef web/lib/django/db/models/sql/expressions.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/web/lib/django/db/models/sql/expressions.py	Wed Jan 20 00:34:04 2010 +0100
@@ -0,0 +1,88 @@
+from django.core.exceptions import FieldError
+from django.db import connection
+from django.db.models.fields import FieldDoesNotExist
+from django.db.models.sql.constants import LOOKUP_SEP
+
+class SQLEvaluator(object):
+    def __init__(self, expression, query, allow_joins=True):
+        self.expression = expression
+        self.opts = query.get_meta()
+        self.cols = {}
+
+        self.contains_aggregate = False
+        self.expression.prepare(self, query, allow_joins)
+
+    def as_sql(self, qn=None):
+        return self.expression.evaluate(self, qn)
+
+    def relabel_aliases(self, change_map):
+        for node, col in self.cols.items():
+            self.cols[node] = (change_map.get(col[0], col[0]), col[1])
+
+    #####################################################
+    # Vistor methods for initial expression preparation #
+    #####################################################
+
+    def prepare_node(self, node, query, allow_joins):
+        for child in node.children:
+            if hasattr(child, 'prepare'):
+                child.prepare(self, query, allow_joins)
+
+    def prepare_leaf(self, node, query, allow_joins):
+        if not allow_joins and LOOKUP_SEP in node.name:
+            raise FieldError("Joined field references are not permitted in this query")
+
+        field_list = node.name.split(LOOKUP_SEP)
+        if (len(field_list) == 1 and
+            node.name in query.aggregate_select.keys()):
+            self.contains_aggregate = True
+            self.cols[node] = query.aggregate_select[node.name]
+        else:
+            try:
+                field, source, opts, join_list, last, _ = query.setup_joins(
+                    field_list, query.get_meta(),
+                    query.get_initial_alias(), False)
+                col, _, join_list = query.trim_joins(source, join_list, last, False)
+
+                self.cols[node] = (join_list[-1], col)
+            except FieldDoesNotExist:
+                raise FieldError("Cannot resolve keyword %r into field. "
+                                 "Choices are: %s" % (self.name,
+                                                      [f.name for f in self.opts.fields]))
+
+    ##################################################
+    # Vistor methods for final expression evaluation #
+    ##################################################
+
+    def evaluate_node(self, node, qn):
+        if not qn:
+            qn = connection.ops.quote_name
+
+        expressions = []
+        expression_params = []
+        for child in node.children:
+            if hasattr(child, 'evaluate'):
+                sql, params = child.evaluate(self, qn)
+            else:
+                sql, params = '%s', (child,)
+
+            if len(getattr(child, 'children', [])) > 1:
+                format = '(%s)'
+            else:
+                format = '%s'
+
+            if sql:
+                expressions.append(format % sql)
+                expression_params.extend(params)
+
+        return connection.ops.combine_expression(node.connector, expressions), expression_params
+
+    def evaluate_leaf(self, node, qn):
+        if not qn:
+            qn = connection.ops.quote_name
+
+        col = self.cols[node]
+        if hasattr(col, 'as_sql'):
+            return col.as_sql(qn), ()
+        else:
+            return '%s.%s' % (qn(col[0]), qn(col[1])), ()