- Fixed potential issue where a custom subclass

of :class:`.FunctionElement` or other column element that incorrectly
states 'None' or any other invalid object as the ``.type``
attribute will report this exception instead of recursion overflow.
fixes #3485

3 files changed, 31 insertions, 3 deletions

diff --git a/doc/build/changelog/changelog_10.rst b/doc/build/changelog/changelog_10.rst
index 48626a525..c4d9ab448 100644
--- a/doc/build/changelog/changelog_10.rst
+++ b/doc/build/changelog/changelog_10.rst
@@ -20,6 +20,15 @@
 
     .. change::
         :tags: bug, sql
+        :tickets: 3485
+
+        Fixed potential issue where a custom subclass
+        of :class:`.FunctionElement` or other column element that incorrectly
+        states 'None' or any other invalid object as the ``.type``
+        attribute will report this exception instead of recursion overflow.
+
+    .. change::
+        :tags: bug, sql
         :pullreq: github:188
 
         Fixed bug where the modulus SQL operator wouldn't work in reverse
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index 27ecce2b0..41dfcf147 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -715,7 +715,14 @@ class ColumnElement(operators.ColumnOperators, ClauseElement):
 
     @util.memoized_property
     def comparator(self):
-        return self.type.comparator_factory(self)
+        try:
+            comparator_factory = self.type.comparator_factory
+        except AttributeError:
+            raise TypeError(
+                "Object %r associated with '.type' attribute "
+                "is not a TypeEngine class or object" % self.type)
+        else:
+            return comparator_factory(self)
 
     def __getattr__(self, key):
         try:
diff --git a/test/sql/test_functions.py b/test/sql/test_functions.py
index ec8d9b5c0..ccc9b2dcd 100644
--- a/test/sql/test_functions.py
+++ b/test/sql/test_functions.py
@@ -9,12 +9,12 @@ from sqlalchemy.sql.compiler import BIND_TEMPLATES
 from sqlalchemy.testing.engines import all_dialects
 from sqlalchemy import types as sqltypes
 from sqlalchemy.sql import functions
-from sqlalchemy.sql.functions import GenericFunction
+from sqlalchemy.sql.functions import GenericFunction, FunctionElement
 import decimal
 from sqlalchemy import testing
 from sqlalchemy.testing import fixtures, AssertsCompiledSQL, engines
 from sqlalchemy.dialects import sqlite, postgresql, mysql, oracle
-
+from sqlalchemy.testing import assert_raises_message
 
 table1 = table('mytable',
                column('myid', Integer),
@@ -477,6 +477,18 @@ class CompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "AS anon_1 FROM mytable"
         )
 
+    def test_incorrect_none_type(self):
+        class MissingType(FunctionElement):
+            name = 'mt'
+            type = None
+
+        assert_raises_message(
+            TypeError,
+            "Object None associated with '.type' attribute is "
+            "not a TypeEngine class or object",
+            MissingType().compile
+        )
+
 
 class ExecuteTest(fixtures.TestBase):