From bd3d4e1df9087ffe8a1799b30b5a09d870511653 Mon Sep 17 00:00:00 2001
From: Derek Anderson <derek@hvst.com>
Date: Fri, 21 Apr 2017 14:07:48 -0500
Subject: [PATCH 1/3] impl prefetched

---
 peewee.py                             | 10 +++++++
 playhouse/tests/test_query_results.py | 39 +++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/peewee.py b/peewee.py
index ae092b5bd..7286cb48d 100644
--- a/peewee.py
+++ b/peewee.py
@@ -5175,6 +5175,16 @@ def save(self, force_insert=False, only=None):
     def is_dirty(self):
         return bool(self._dirty)
 
+    def prefetched(self, fk):
+        '''
+            Accepts a ForeignKeyField.
+            Returns true/false representing if accessing this attribute will trigger a database query. 
+        '''
+        if not isinstance(self, fk.model_class):
+          raise AttributeError('ForeignKeyField %s is not part of this model.' % fk)
+        if getattr(self, fk.db_column) is None: return True
+        return fk.name in self._obj_cache
+
     @property
     def dirty_fields(self):
         return [f for f in self._meta.sorted_fields if f.name in self._dirty]
diff --git a/playhouse/tests/test_query_results.py b/playhouse/tests/test_query_results.py
index 3d726a61c..b7c6c0fb2 100644
--- a/playhouse/tests/test_query_results.py
+++ b/playhouse/tests/test_query_results.py
@@ -484,6 +484,45 @@ def test_aliasing_values(self):
         self.assertEqual(results, [('u1', 'u1'), ('u2', 'u2')])
 
 
+class TestPrefetchDetection(ModelTestCase):
+    requires = [Parent, Child, Orphan]
+
+    def setUp(self):
+        super(TestPrefetchDetection, self).setUp()
+        u1 = Parent.create(data='u1')
+        u2 = Child.create(parent=u1, data='u2')
+        u3 = Orphan.create(data='u3')
+
+    def test_prefetched(self):
+        u2 = (Child
+             .select(Child, Parent)
+             .join(Parent)
+             .first())
+        self.assertTrue(u2.prefetched(Child.parent))
+
+    def test_not_prefetched(self):
+        u2 = Child.select().first()
+        self.assertFalse(u2.prefetched(Child.parent))
+
+    def test_prefetched_null(self):
+        u3 = (Orphan
+             .select(Orphan, Parent)
+             .join(Parent, JOIN.LEFT_OUTER)
+             .first())
+        self.assertTrue(u3.prefetched(Orphan.parent))
+
+    def test_not_prefetched_null(self):
+        u3 = Orphan.select().first()
+        # even though it's not joined, we know the model
+        # is null because the FK value is null.
+        self.assertTrue(u3.prefetched(Orphan.parent))
+
+    def test_prefetched_nonsense(self):
+        u1 = Parent.select().first()
+        with self.assertRaises(AttributeError):
+          u1.prefetched(Orphan.parent)
+
+
 class TestJoinedInstanceConstruction(ModelTestCase):
     requires = [Blog, User, Relationship]
 

From fab9771f1cdadedc8f32f1face2d3406f85a349b Mon Sep 17 00:00:00 2001
From: Derek Anderson <derek@hvst.com>
Date: Fri, 21 Apr 2017 14:42:42 -0500
Subject: [PATCH 2/3] impl prefetched for reverse relationships

---
 peewee.py                             | 10 ++++++----
 playhouse/tests/test_query_results.py |  9 +++++++--
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/peewee.py b/peewee.py
index 7286cb48d..29fc64612 100644
--- a/peewee.py
+++ b/peewee.py
@@ -5180,10 +5180,12 @@ def prefetched(self, fk):
             Accepts a ForeignKeyField.
             Returns true/false representing if accessing this attribute will trigger a database query. 
         '''
-        if not isinstance(self, fk.model_class):
-          raise AttributeError('ForeignKeyField %s is not part of this model.' % fk)
-        if getattr(self, fk.db_column) is None: return True
-        return fk.name in self._obj_cache
+        if isinstance(self, fk.model_class):
+            if getattr(self, fk.db_column) is None: return True
+            return fk.name in self._obj_cache
+        if isinstance(self, fk.rel_model):
+            return isinstance(getattr(self, fk._get_related_name()), list)
+        raise AttributeError('ForeignKeyField %s is not related to this model.' % fk)
 
     @property
     def dirty_fields(self):
diff --git a/playhouse/tests/test_query_results.py b/playhouse/tests/test_query_results.py
index b7c6c0fb2..1e6c7ee25 100644
--- a/playhouse/tests/test_query_results.py
+++ b/playhouse/tests/test_query_results.py
@@ -518,9 +518,14 @@ def test_not_prefetched_null(self):
         self.assertTrue(u3.prefetched(Orphan.parent))
 
     def test_prefetched_nonsense(self):
-        u1 = Parent.select().first()
+        u2 = Child.select().first()
         with self.assertRaises(AttributeError):
-          u1.prefetched(Orphan.parent)
+          u2.prefetched(Orphan.parent)
+
+    def test_prefetched_set(self):
+        u2 = Parent.ALL.plus(Child.parent).first()
+        self.assertTrue(u2.prefetched(Child.parent))
+
 
 
 class TestJoinedInstanceConstruction(ModelTestCase):

From 6b55503f710523db7fa764d3e4532b312aa5dc2d Mon Sep 17 00:00:00 2001
From: Derek Anderson <derek@hvst.com>
Date: Fri, 21 Apr 2017 14:45:02 -0500
Subject: [PATCH 3/3] python2.6 fix

---
 playhouse/tests/test_query_results.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/playhouse/tests/test_query_results.py b/playhouse/tests/test_query_results.py
index 1e6c7ee25..0795b478f 100644
--- a/playhouse/tests/test_query_results.py
+++ b/playhouse/tests/test_query_results.py
@@ -519,8 +519,9 @@ def test_not_prefetched_null(self):
 
     def test_prefetched_nonsense(self):
         u2 = Child.select().first()
-        with self.assertRaises(AttributeError):
+        def f():
           u2.prefetched(Orphan.parent)
+        self.assertRaises(AttributeError, f)
 
     def test_prefetched_set(self):
         u2 = Parent.ALL.plus(Child.parent).first()