Make CI comparator smarter

CHANGES.rst

@@ -4,6 +4,12 @@ Changelog
 Here you can see the full list of changes between each SQLAlchemy-Utils release.
 
 
+0.29.4 (2015-01-31)
+^^^^^^^^^^^^^^^^^^^
+
+- Made CaseInsensitiveComparator not cast already lowercased types to lowercase
+
+
 0.29.3 (2015-01-24)
 ^^^^^^^^^^^^^^^^^^^
 

sqlalchemy_utils/operators.py

@@ -1,17 +1,41 @@
 import sqlalchemy as sa
 
 
+def inspect_type(mixed):
+    if isinstance(mixed, sa.orm.attributes.InstrumentedAttribute):
+        return mixed.property.columns[0].type
+    elif isinstance(mixed, sa.orm.ColumnProperty):
+        return mixed.columns[0].type
+    elif isinstance(mixed, sa.Column):
+        return mixed.type
+
+
+def is_case_insensitive(mixed):
+    try:
+        return isinstance(
+            inspect_type(mixed).comparator,
+            CaseInsensitiveComparator
+        )
+    except AttributeError:
+        try:
+            return issubclass(
+                inspect_type(mixed).comparator_factory,
+                CaseInsensitiveComparator
+            )
+        except AttributeError:
+            return False
+
+
 class CaseInsensitiveComparator(sa.Unicode.Comparator):
     @classmethod
     def lowercase_arg(cls, func):
         def operation(self, other, **kwargs):
+            operator = getattr(sa.Unicode.Comparator, func)
             if other is None:
-                return getattr(sa.Unicode.Comparator, func)(
-                    self, other, **kwargs
-                )
-            return getattr(sa.Unicode.Comparator, func)(
-                self, sa.func.lower(other), **kwargs
-            )
+                return operator(self, other, **kwargs)
+            if not is_case_insensitive(other):
+                other = sa.func.lower(other)
+            return operator(self, other, **kwargs)
         return operation
 
     def in_(self, other):

tests/test_case_insensitive_comparator.py

@@ -42,3 +42,8 @@ class TestCaseInsensitiveComparator(TestCase):
             '"user".email NOT IN (lower(:lower_1), lower(:lower_2))'
             in str(query)
         )
+
+    def test_does_not_apply_lower_to_types_that_are_already_lowercased(self):
+        assert str(self.User.email == self.User.email) == (
+            '"user".email = "user".email'
+        )