Change translation hybrid expr

Change translation hybrid expression to return the current translation if it exists
and otherwise fallback to default translation.

CHANGES.rst

@@ -4,6 +4,12 @@ Changelog
 Here you can see the full list of changes between each SQLAlchemy-Utils release.
 
 
+0.30.1 (2015-05-xx)
+^^^^^^^^^^^^^^^^^^^
+
+- Make translation_hybrid expression work the same way as SQLAlchemy-i18n translation expressions
+
+
 0.30.0 (2015-04-15)
 ^^^^^^^^^^^^^^^^^^^
 

sqlalchemy_utils/i18n.py

@@ -1,3 +1,4 @@
+import sqlalchemy as sa
 from sqlalchemy.ext.hybrid import hybrid_property
 
 from .exceptions import ImproperlyConfigured
@@ -71,7 +72,11 @@ class TranslationHybrid(object):
         return setter
 
     def expr_factory(self, attr):
-        return lambda cls: attr
+        def expr(cls):
+            current_locale = self.cast_locale(cls, self.current_locale)
+            default_locale = self.cast_locale(cls, self.default_locale)
+            return sa.func.coalesce(attr[current_locale], attr[default_locale])
+        return expr
 
     def __call__(self, attr):
         return hybrid_property(

tests/test_translation_hybrid.py

@@ -1,4 +1,5 @@
 import sqlalchemy as sa
+from pytest import mark
 from sqlalchemy.dialects.postgresql import HSTORE
 
 from sqlalchemy_utils import TranslationHybrid
@@ -26,9 +27,6 @@ class TestTranslationHybrid(TestCase):
         city = self.City(name='Helsinki')
         assert city.name_translations['fi'] == 'Helsinki'
 
-    def test_hybrid_as_expression(self):
-        assert self.City.name == self.City.name_translations
-
     def test_if_no_translation_exists_returns_none(self):
         city = self.City()
         assert city.name is None
@@ -52,11 +50,18 @@ class TestTranslationHybrid(TestCase):
 
         assert city.name == 'Helsinki'
 
-    def test_hybrid_as_an_expression(self):
-        city = self.City(name_translations={'en': 'Helsinki'})
+    @mark.parametrize(
+        ('name_translations', 'name'),
+        (
+            ({'fi': 'Helsinki', 'en': 'Helsing'}, 'Helsinki'),
+            ({'en': 'Helsinki'}, 'Helsinki'),
+            ({'fi': 'Helsinki'}, 'Helsinki'),
+            ({}, None),
+        )
+    )
+    def test_hybrid_as_an_expression(self, name_translations, name):
+        city = self.City(name_translations=name_translations)
         self.session.add(city)
         self.session.commit()
 
-        assert city == self.session.query(self.City).filter(
-            self.City.name['en'] == 'Helsinki'
-        ).first()
+        assert self.session.query(self.City.name).scalar() == name