From ae14380e21ce31b0b3408f357dc75c75a3e95be9 Mon Sep 17 00:00:00 2001
From: Konsta Vesterinen <konsta.vesterinen@gmail.com>
Date: Mon, 26 Oct 2015 14:16:58 +0200
Subject: [PATCH] Fix observer notification on column properties, fixes #138

---
 sqlalchemy_utils/__init__.py           |  2 +-
 sqlalchemy_utils/observer.py           | 34 +++++++++++++++-----------
 tests/observes/test_column_property.py | 27 ++++++++++++++++++++
 3 files changed, 48 insertions(+), 15 deletions(-)

diff --git a/sqlalchemy_utils/__init__.py b/sqlalchemy_utils/__init__.py
index de30ed3..9e2c582 100644
--- a/sqlalchemy_utils/__init__.py
+++ b/sqlalchemy_utils/__init__.py
@@ -93,4 +93,4 @@ from .types import (  # noqa
     WeekDaysType
 )
 
-__version__ = '0.31.0'
+__version__ = '0.31.1'
diff --git a/sqlalchemy_utils/observer.py b/sqlalchemy_utils/observer.py
index c109480..bd7c1de 100644
--- a/sqlalchemy_utils/observer.py
+++ b/sqlalchemy_utils/observer.py
@@ -154,7 +154,7 @@ from collections import defaultdict, Iterable, namedtuple
 
 import sqlalchemy as sa
 
-from sqlalchemy_utils.functions import getdotattr
+from sqlalchemy_utils.functions import getdotattr, has_changes
 from sqlalchemy_utils.path import AttrPath
 from sqlalchemy_utils.utils import is_sequence
 
@@ -236,7 +236,6 @@ class PropertyObserver(object):
                         )
 
     def gather_callback_args(self, obj, callbacks):
-        session = sa.orm.object_session(obj)
         for callback in callbacks:
             backref = callback.backref
 
@@ -246,19 +245,26 @@ class PropertyObserver(object):
                     root_objs = [root_objs]
 
                 for root_obj in root_objs:
-                    objects = getdotattr(
-                        root_obj,
-                        callback.fullpath,
-                        lambda obj: obj not in session.deleted
-                    )
+                    args = self.get_callback_args(root_obj, callback)
+                    if args:
+                        yield args
 
-                    yield (
-                        root_obj,
-                        callback.func,
-                        objects
-                    )
+    def get_callback_args(self, root_obj, callback):
+        session = sa.orm.object_session(root_obj)
+        objects = getdotattr(
+            root_obj,
+            callback.fullpath,
+            lambda obj: obj not in session.deleted
+        )
+        path = str(callback.fullpath)
+        if '.' in path or has_changes(root_obj, path):
+            return (
+                root_obj,
+                callback.func,
+                objects
+            )
 
-    def changed_objects(self, session):
+    def iterate_objects_and_callbacks(self, session):
         objs = itertools.chain(session.new, session.dirty, session.deleted)
         for obj in objs:
             for class_, callbacks in self.callback_map.items():
@@ -267,7 +273,7 @@ class PropertyObserver(object):
 
     def invoke_callbacks(self, session, ctx, instances):
         callback_args = defaultdict(lambda: defaultdict(set))
-        for obj, callbacks in self.changed_objects(session):
+        for obj, callbacks in self.iterate_objects_and_callbacks(session):
             args = self.gather_callback_args(obj, callbacks)
             for (root_obj, func, objects) in args:
                 if is_sequence(objects):
diff --git a/tests/observes/test_column_property.py b/tests/observes/test_column_property.py
index 8339f4b..058383a 100644
--- a/tests/observes/test_column_property.py
+++ b/tests/observes/test_column_property.py
@@ -1,4 +1,5 @@
 import sqlalchemy as sa
+from pytest import raises
 
 from sqlalchemy_utils.observer import observes
 from tests import TestCase
@@ -24,3 +25,29 @@ class TestObservesForColumn(TestCase):
         self.session.add(product)
         self.session.flush()
         assert product.price == 200
+
+
+class TestObservesForColumnWithoutActualChanges(TestCase):
+    dns = 'postgres://postgres@localhost/sqlalchemy_utils_test'
+
+    def create_models(self):
+        class Product(self.Base):
+            __tablename__ = 'product'
+            id = sa.Column(sa.Integer, primary_key=True)
+            price = sa.Column(sa.Integer)
+
+            @observes('price')
+            def product_price_observer(self, price):
+                raise Exception('Trying to change price')
+
+        self.Product = Product
+
+    def test_only_notifies_observer_on_actual_changes(self):
+        product = self.Product()
+        self.session.add(product)
+        self.session.flush()
+
+        with raises(Exception) as e:
+            product.price = 500
+            self.session.commit()
+        assert str(e.value) == 'Trying to change price'