1) Fixed bugs

2) Edited the docs
3) Added test for prewhere

docs/querysets.md

@@ -17,21 +17,29 @@ The `filter` and `exclude` methods are used for filtering the matching instances
 
     >>> qs = Person.objects_in(database)
     >>> qs = qs.filter(first_name__startswith='V').exclude(birthday__lt='2000-01-01')
-    >>> qs.conditions_as_sql()
+    >>> qs.conditions_as_sql(qs._where)
     u"first_name LIKE 'V%' AND NOT (birthday < '2000-01-01')"
 
 It is possible to specify several fields to filter or exclude by:
 
     >>> qs = Person.objects_in(database).filter(last_name='Smith', height__gt=1.75)
-    >>> qs.conditions_as_sql()
+    >>> qs.conditions_as_sql(qs._where)
     u"last_name = 'Smith' AND height > 1.75"
 
 For filters with compound conditions you can use `Q` objects inside `filter` with overloaded operators `&` (AND), `|` (OR) and `~` (NOT):
 
     >>> qs = Person.objects_in(database).filter((Q(first_name='Ciaran', last_name='Carver') | Q(height_lte=1.8)) & ~Q(first_name='David'))
-    >>> qs.conditions_as_sql()
+    >>> qs.conditions_as_sql(qs._where)
     u"((first_name = 'Ciaran' AND last_name = 'Carver') OR height <= 1.8) AND (NOT (first_name = 'David'))"
 
+By default conditions from `filter` and `exclude` methods are add to `WHERE` clause. 
+For better aggregation performance you can add them to `PREWHERE` section using `prewhere=True` parameter
+
+    >>> qs = Person.objects_in(database)
+    >>> qs = qs.filter(first_name__startswith='V', prewhere=True)
+    >>> qs.conditions_as_sql(qs._prewhere)
+    u"first_name LIKE 'V%'"
+    
 There are different operators that can be used, by passing `<fieldname>__<operator>=<value>` (two underscores separate the field name from the operator). In case no operator is given, `eq` is used by default. Below are all the supported operators.
 
 | Operator       | Equivalent SQL                               | Comments                           |

src/infi/clickhouse_orm/query.py

@@ -189,14 +189,14 @@ class Q(object):
         Checks if there are any conditions in Q object
         :return: Boolean
         """
-        return bool(self._fovs or self._l_child or self._r_child)
+        return not bool(self._fovs or self._l_child or self._r_child)
 
     @classmethod
     def _construct_from(cls, l_child, r_child, mode):
         q = Q()
         q._l_child = l_child
         q._r_child = r_child
-        q._mode = mode # AND/OR
+        q._mode = mode  # AND/OR
         return q
 
     def _build_fov(self, key, value):
@@ -209,14 +209,17 @@ class Q(object):
     def to_sql(self, model_cls):
         if self._fovs:
             sql = ' {} '.format(self._mode).join(fov.to_sql(model_cls) for fov in self._fovs)
+        elif self._l_child and self._r_child:
+            sql = '({}) {} ({})'.format(self._l_child.to_sql(model_cls), self._mode, self._r_child.to_sql(model_cls))
+        elif self._l_child or self._r_child:
+            # Return existing condition
+            sql = (self._l_child or self._r_child).to_sql(model_cls)
         else:
-            if self._l_child and self._r_child:
-                sql = '({}) {} ({})'.format(
-                        self._l_child.to_sql(model_cls), self._mode, self._r_child.to_sql(model_cls))
-            else:
-                return '1'
+            sql = '1'
+
         if self._negate:
             sql = 'NOT (%s)' % sql
+
         return sql
 
     def __or__(self, other):
@@ -303,7 +306,7 @@ class QuerySet(object):
         distinct = 'DISTINCT ' if self._distinct else ''
 
         params = (distinct, self.select_fields_as_sql(), self._model_cls.table_name())
-        sql = u'SELECT %s%s\nFROM `%s`\n' % params
+        sql = u'SELECT %s%s\nFROM `%s`' % params
 
         if self._prewhere_q:
             sql += '\nPREWHERE ' + self.conditions_as_sql(self._prewhere_q)
@@ -320,7 +323,7 @@ class QuerySet(object):
         if self._limits:
             sql += '\nLIMIT %d, %d' % self._limits
 
-        return
+        return sql
 
     def order_by_as_sql(self):
         """
@@ -335,10 +338,7 @@ class QuerySet(object):
         """
         Returns the contents of the query's `WHERE` or `PREWHERE` clause as a string.
         """
-        if q_object:
-            return u' AND '.join([q.to_sql(self._model_cls) for q in q_object])
-        else:
-            return u''
+        return q_object.to_sql(self._model_cls)
 
     def count(self):
         """
@@ -378,8 +378,8 @@ class QuerySet(object):
         condition = copy(self._where_q)
         qs = copy(self)
 
-        if q:
-            condition &= q
+        for q_obj in q:
+            condition &= q_obj
 
         if kwargs:
             condition &= Q(**kwargs)
@@ -487,7 +487,8 @@ class AggregateQuerySet(QuerySet):
         self._grouping_fields = grouping_fields
         self._calculated_fields = calculated_fields
         self._order_by = list(base_qs._order_by)
-        self._q = list(base_qs._q)
+        self._where_q = base_qs._where_q
+        self._prewhere_q = base_qs._prewhere_q
         self._limits = base_qs._limits
         self._distinct = base_qs._distinct
 

tests/test_querysets.py

@@ -11,7 +11,7 @@ from datetime import date, datetime
 try:
     Enum # exists in Python 3.4+
 except NameError:
-    from enum import Enum # use the enum34 library instead
+    from enum import Enum  # use the enum34 library instead
 
 
 class QuerySetTestCase(TestCaseWithData):
@@ -29,6 +29,13 @@ class QuerySetTestCase(TestCaseWithData):
         self.assertEqual(count, expected_count)
         self.assertEqual(qs.count(), expected_count)
 
+    def test_prewhere(self):
+        # We can't distinguish prewhere and where results, it affects performance only.
+        # So let's control prewhere acts like where does
+        qs = Person.objects_in(self.database)
+        self.assertTrue(qs.filter(first_name='Connor', prewhere=True))
+        self.assertFalse(qs.filter(first_name='Willy', prewhere=True))
+
     def test_no_filtering(self):
         qs = Person.objects_in(self.database)
         self._test_qs(qs, len(data))