don't enable "fast insert executemany" for ON CONFLICT etc

Fixed issue where using the PostgreSQL "INSERT..ON CONFLICT" structure
would fail to work with the psycopg2 driver if it were used in an
"executemany" context along with bound parameters in the "SET" clause, due
to the implicit use of the psycopg2 fast execution helpers which are not
appropriate for this style of INSERT statement. Additional checks to
exclude this kind of statement from that particular extension have been
added.

Fixes: #6581
Change-Id: I3d6169e7e188dc087d1d1bfba9a42162db183265

3 files changed, 48 insertions, 1 deletions

diff --git a/doc/build/changelog/unreleased_14/6581.rst b/doc/build/changelog/unreleased_14/6581.rst
new file mode 100644
index 000000000..643892b6a
--- /dev/null
+++ b/doc/build/changelog/unreleased_14/6581.rst
@@ -0,0 +1,11 @@
+.. change::
+    :tags: bug, postgresql
+    :tickets: 6581
+
+    Fixed issue where using the PostgreSQL "INSERT..ON CONFLICT" structure
+    would fail to work with the psycopg2 driver if it were used in an
+    "executemany" context along with bound parameters in the "SET" clause, due
+    to the implicit use of the psycopg2 fast execution helpers which are not
+    appropriate for this style of INSERT statement. Additional checks to
+    exclude this kind of statement from that particular extension have been
+    added.
diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index 734e65492..220a0fa99 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -3588,7 +3588,14 @@ class SQLCompiler(Compiled):
                 [value for c, expr, value in crud_params]
             )
             text += " VALUES (%s)" % insert_single_values_expr
-            if toplevel:
+            if toplevel and insert_stmt._post_values_clause is None:
+                # don't assign insert_single_values_expr if _post_values_clause
+                # is present.  what this means concretely is that the
+                # "fast insert executemany helper" won't be used, in other
+                # words we won't convert "executemany()" of many parameter
+                # sets into a single INSERT with many elements in VALUES.
+                # We can't apply that optimization safely if for example the
+                # statement includes a clause like "ON CONFLICT DO UPDATE"
                 self.insert_single_values_expr = insert_single_values_expr
 
         if insert_stmt._post_values_clause is not None:
diff --git a/test/dialect/postgresql/test_on_conflict.py b/test/dialect/postgresql/test_on_conflict.py
index dcf112de6..508f691c5 100644
--- a/test/dialect/postgresql/test_on_conflict.py
+++ b/test/dialect/postgresql/test_on_conflict.py
@@ -206,6 +206,35 @@ class OnConflictTest(fixtures.TablesTest):
             [(1, "name1")],
         )
 
+    def test_on_conflict_do_update_set_executemany(self, connection):
+        """test #6581"""
+
+        users = self.tables.users
+
+        connection.execute(
+            users.insert(),
+            [dict(id=1, name="name1"), dict(id=2, name="name2")],
+        )
+
+        i = insert(users)
+        i = i.on_conflict_do_update(
+            index_elements=[users.c.id],
+            set_={"id": i.excluded.id, "name": i.excluded.name + ".5"},
+        )
+        connection.execute(
+            i,
+            [
+                dict(id=1, name="name1"),
+                dict(id=2, name="name2"),
+                dict(id=3, name="name3"),
+            ],
+        )
+
+        eq_(
+            connection.execute(users.select().order_by(users.c.id)).fetchall(),
+            [(1, "name1.5"), (2, "name2.5"), (3, "name3")],
+        )
+
     def test_on_conflict_do_update_schema(self, connection):
         users = self.tables.get("%s.users_schema" % config.test_schema)