Add force_instant_defaults listener

sqlalchemy_utils/listeners.py

@@ -17,3 +17,20 @@ def coercion_listener(mapper, class_):
             listener,
             retval=True
         )
+
+
+def instant_defaults_listener(target, args, kwargs):
+    for key, column in sa.inspect(target.__class__).columns.items():
+        if column.default is not None:
+            if callable(column.default.arg):
+                setattr(target, key, column.default.arg(target))
+            else:
+                setattr(target, key, column.default.arg)
+
+
+def coerce_data_types(mapper=sa.orm.mapper):
+    sa.event.listen(mapper, 'mapper_configured', coercion_listener)
+
+
+def force_instant_defaults(mapper=sa.orm.mapper):
+    sa.event.listen(mapper, 'init', instant_defaults_listener)

tests/test_instant_defaults_listener.py

@@ -0,0 +1,26 @@
+from datetime import datetime
+import sqlalchemy as sa
+from sqlalchemy_utils.listeners import force_instant_defaults
+from tests import TestCase
+
+
+force_instant_defaults()
+
+
+class TestInstantDefaultListener(TestCase):
+    def create_models(self):
+        class Article(self.Base):
+            __tablename__ = 'article'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255), default=u'Some article')
+            created_at = sa.Column(sa.DateTime, default=datetime.now)
+
+        self.Article = Article
+
+    def test_assigns_defaults_on_object_construction(self):
+        article = self.Article()
+        assert article.name == u'Some article'
+
+    def test_callables_as_defaults(self):
+        article = self.Article()
+        assert isinstance(article.created_at, datetime)