Ensure no compiler visit method tries to access .statement

Fixed structural compiler issue where some constructs such as MySQL /
PostgreSQL "on conflict / on duplicate key" would rely upon the state of
the :class:`_sql.Compiler` object being fixed against their statement as
the top level statement, which would fail in cases where those statements
are branched from a different context, such as a DDL construct linked to a
SQL statement.

Fixes: #5656
Change-Id: I568bf40adc7edcf72ea6c7fd6eb9d07790de189e

1 files changed, 6 insertions, 6 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 3e6c676ab..77f65799c 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -1461,6 +1461,8 @@ class MySQLCompiler(compiler.SQLCompiler):
         return self._render_json_extract_from_binary(binary, operator, **kw)
 
     def visit_on_duplicate_key_update(self, on_duplicate, **kw):
+        statement = self.current_executable
+
         if on_duplicate._parameter_ordering:
             parameter_ordering = [
                 coercions.expect(roles.DMLColumnRole, key)
@@ -1468,14 +1470,12 @@ class MySQLCompiler(compiler.SQLCompiler):
             ]
             ordered_keys = set(parameter_ordering)
             cols = [
-                self.statement.table.c[key]
+                statement.table.c[key]
                 for key in parameter_ordering
-                if key in self.statement.table.c
-            ] + [
-                c for c in self.statement.table.c if c.key not in ordered_keys
-            ]
+                if key in statement.table.c
+            ] + [c for c in statement.table.c if c.key not in ordered_keys]
         else:
-            cols = self.statement.table.c
+            cols = statement.table.c
 
         clauses = []
         # traverses through all table columns to preserve table column order