Ticket #3283: empty_in_clause.patch

query.py

@@ -25 +25 @@
 # Larger values are slightly faster at the expense of more storage space.
 GET_ITERATOR_CHUNK_SIZE = 100
 
+class EmptyInClause(Exception):
+    pass
+
 ####################
 # HELPER FUNCTIONS #
 ####################
@@ -168 +171 @@
         extra_select = self._select.items()
 
         cursor = connection.cursor()
-        select, sql, params = self._get_sql_clause()
+
+        try:
+            select, sql, params = self._get_sql_clause()
+        except EmptyInClause:
+            raise StopIteration
+
         cursor.execute("SELECT " + (self._distinct and "DISTINCT " or "") + ",".join(select) + sql, params)
         fill_cache = self._select_related
         index_end = len(self.model._meta.fields)
@@ -192 +200 @@
         counter._offset = None
         counter._limit = None
         counter._select_related = False
-        select, sql, params = counter._get_sql_clause()
+
+        try:
+            select, sql, params = counter._get_sql_clause()
+        except EmptyInClause:
+            return 0
+
         cursor = connection.cursor()
         if self._distinct:
             id_col = "%s.%s" % (backend.quote_name(self.model._meta.db_table),
@@ -523 +536 @@
             field_names = [f.attname for f in self.model._meta.fields]
 
         cursor = connection.cursor()
-        select, sql, params = self._get_sql_clause()
+
+        try:
+            select, sql, params = self._get_sql_clause()
+        except EmptyInClause:
+            raise StopIteration
+
         select = ['%s.%s' % (backend.quote_name(self.model._meta.db_table), backend.quote_name(c)) for c in columns]
         cursor.execute("SELECT " + (self._distinct and "DISTINCT " or "") + ",".join(select) + sql, params)
         while 1:
@@ -545 +563 @@
         if self._field.null:
             self._where.append('%s.%s IS NOT NULL' % \
                 (backend.quote_name(self.model._meta.db_table), backend.quote_name(self._field.column)))
-        select, sql, params = self._get_sql_clause()
+
+        try:
+            select, sql, params = self._get_sql_clause()
+        except EmptyInClause:
+            raise StopIteration
+
         sql = 'SELECT %s %s GROUP BY 1 ORDER BY 1 %s' % \
             (backend.get_date_trunc_sql(self._kind, '%s.%s' % (backend.quote_name(self.model._meta.db_table),
             backend.quote_name(self._field.column))), sql, self._order)
@@ -645 +687 @@
         if in_string:
             return '%s%s IN (%s)' % (table_prefix, field_name, in_string)
         else:
-            # Most backends do not accept an empty string inside the IN
-            # expression, i.e. cannot do "WHERE ... IN ()".  Since there are
-            # also some backends that do not accept "WHERE false", we instead
-            # use an expression that always evaluates to False.
-            return '0=1'
+            raise EmptyInClause
     elif lookup_type == 'range':
         return '%s%s BETWEEN %%s AND %%s' % (table_prefix, field_name)
     elif lookup_type in ('year', 'month', 'day'):