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

2 files changed, 13 insertions, 1 deletions

diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index c7d574a21..1c10f484f 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -1073,7 +1073,11 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
             # TODO: expensive branching here should be
             # pulled into _exec_scalar()
             conn = self.connection
-            c = expression.select([default.arg]).compile(bind=conn)
+            if not default._arg_is_typed:
+                default_arg = expression.type_coerce(default.arg, type_)
+            else:
+                default_arg = default.arg
+            c = expression.select([default_arg]).compile(bind=conn)
             return conn._execute_compiled(c, (), {}).scalar()
         else:
             return default.arg
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.