Handle SQL commands executed using as psycopg2 Composed object

The Composed object is the recommended way of composing SQL statements.
The SQL panel is currently expecting an string sql. Executing a composed
sql command will cause the following exception:

```
======================================================================
ERROR: test_execute_with_psycopg2_composed_sql (tests.panels.test_sql.SQLPanelTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/haki/src/django-debug-toolbar/tests/panels/test_sql.py", line 228, in test_execute_with_psycopg2_composed_sql
    cursor.execute(command)
  File "/home/haki/src/django-debug-toolbar/debug_toolbar/panels/sql/tracking.py", line 184, in execute
    return self._record(self.cursor.execute, sql, params)
  File "/home/haki/src/django-debug-toolbar/debug_toolbar/panels/sql/tracking.py", line 156, in _record
    "is_select": sql.lower().strip().startswith("select"),
AttributeError: 'Composed' object has no attribute 'lower'
```

The solution is to cast the sql to string. If it's already string - no harm. If it's a
`Composable` object, it will return the composed SQL as str.

Author: hakib

debug_toolbar/panels/sql/tracking.py

@@ -135,6 +135,10 @@ def _record(self, method, sql, params):
             conn = self.db.connection
             vendor = getattr(conn, "vendor", "unknown")
 
+            # Sql might be an object (such as psycopg Composed).
+            # For logging purposes, make sure it's str.
+            sql = str(sql)
+
             params = {
                 "vendor": vendor,
                 "alias": alias,

tests/panels/test_sql.py

@@ -209,6 +209,31 @@ def test_erroneous_query(self):
         except DatabaseError as e:
             self.assertTrue("erroneous query" in str(e))
 
+    @unittest.skipUnless(
+        connection.vendor == "postgresql", "Test valid only on PostgreSQL"
+    )
+    def test_execute_with_psycopg2_composed_sql(self):
+        """
+        Test command executed using a Composed psycopg2 object is logged.
+        Ref: http://initd.org/psycopg/docs/sql.html
+        """
+        from psycopg2 import sql
+
+        self.assertEqual(len(self.panel._queries), 0)
+
+        with connection.cursor() as cursor:
+            command = sql.SQL("select {field} from {table}").format(
+                field=sql.Identifier("username"), table=sql.Identifier("auth_user")
+            )
+            cursor.execute(command)
+
+        self.assertEqual(len(self.panel._queries), 1)
+
+        query = self.panel._queries[0]
+        self.assertEqual(query[0], "default")
+        self.assertTrue("sql" in query[1])
+        self.assertEqual(query[1]["sql"], 'select "username" from "auth_user"')
+
     def test_disable_stacktraces(self):
         self.assertEqual(len(self.panel._queries), 0)