Fix filter() stopping one short in some situations.

Author: coleifer

peewee.py

@@ -8750,7 +8750,8 @@ def convert_dict_to_node(self, qdict):
                 # direct FK lookup is all that is required.
                 model_attr = getattr(curr, key)
             else:
-                for piece in key.split('__'):
+                pieces = key.split('__')
+                for i, piece in enumerate(pieces):
                     try:
                         model_attr = getattr(curr, piece, None)
                     except Exception:
@@ -8762,7 +8763,9 @@ def convert_dict_to_node(self, qdict):
                             break
                     else:
                         model_attr = getattr(curr, piece)
-                        if value is not None and isinstance(model_attr, fks):
+                        # Follow an fk only when a piece remains, the last
+                        # one compares the fk column itself.
+                        if i < len(pieces) - 1 and isinstance(model_attr, fks):
                             curr = model_attr.rel_model
                             joins.append(model_attr)
             accum.append(op(model_attr, value))

tests/model_sql.py

@@ -406,6 +406,22 @@ def test_filter_join(self):
             'INNER JOIN "users" AS "ua" ON ("t1"."user_id" = "ua"."id") '
             'WHERE ("ua"."username" = ?)'), ['huey'])
 
+        # A path ending in None still walks to the last model.
+        query = Tweet.select(Tweet.content).filter(user__username=None)
+        self.assertSQL(query, (
+            'SELECT "t1"."content" FROM "tweet" AS "t1" '
+            'INNER JOIN "users" AS "t2" ON ("t1"."user_id" = "t2"."id") '
+            'WHERE ("t2"."username" IS NULL)'), [])
+
+        # A path ending on a foreign key compares the column and does not
+        # join the related model.
+        for value, clause, params in ((None, 'IS NULL', []), (3, '= ?', [3])):
+            query = Favorite.select(Favorite.id).filter(tweet__user=value)
+            self.assertSQL(query, (
+                'SELECT "t1"."id" FROM "favorite" AS "t1" '
+                'INNER JOIN "tweet" AS "t2" ON ("t1"."tweet_id" = "t2"."id") '
+                'WHERE ("t2"."user_id" %s)' % clause), params)
+
     def test_filter_with_or_across_joins(self):
         query = (Tweet
                  .select(Tweet.content)

tests/models.py

@@ -7630,6 +7630,8 @@ def assertNames(q, expected):
 
         assertNames(DFGC.filter(dfc__df=a), ['a1-1', 'a1-2', 'a2-1'])
         assertNames(DFGC.filter(dfc__df=a.id), ['a1-1', 'a1-2', 'a2-1'])
+        assertNames(DFGC.filter(dfc__df=None), [])
+        assertNames(DFGC.filter(dfc__df__name=None), [])
 
         q = DFC.select().join(DF)
         assertNames(q.filter(df=a), ['a1', 'a2'])