Apply type processing to untyped preexec default clause

Fixed bug where a SQL-oriented Python-side column default could fail to
be executed properly upon INSERT in the "pre-execute" codepath, if the
SQL itself were an untyped expression, such as plain text.  The "pre-
execute" codepath is fairly uncommon however can apply to non-integer
primary key columns with SQL defaults when RETURNING is not used.

Tests exist here to ensure typing is applied to
a typed expression for default, but in the case of
an untyped SQL value, we know the type from the column,
so apply this.

Change-Id: I5d8b391611c137b9f700115a50a2bf5b30abfe94
Fixes: #3923

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/schema.py b/lib/sqlalchemy/sql/schema.py
index f8d3209ef..cf12ce965 100644
--- a/lib/sqlalchemy/sql/schema.py
+++ b/lib/sqlalchemy/sql/schema.py
@@ -2067,6 +2067,14 @@ class ColumnDefault(DefaultGenerator):
             not self.is_clause_element and \
             not self.is_sequence
 
+    @util.memoized_property
+    @util.dependencies("sqlalchemy.sql.sqltypes")
+    def _arg_is_typed(self, sqltypes):
+        if self.is_clause_element:
+            return not isinstance(self.arg.type, sqltypes.NullType)
+        else:
+            return False
+
     def _maybe_wrap_callable(self, fn):
         """Wrap callables that don't accept a context.