Default psycopg2 executemany mode to "values_only"

The psycopg2 dialect now defaults to using the very performant
``execute_values()`` psycopg2 extension for compiled INSERT statements,
and also impements RETURNING support when this extension is used.  This
allows INSERT statements that even include an autoincremented SERIAL
or IDENTITY value to run very fast while still being able to return the
newly generated primary key values.   The ORM will then integrate this
new feature in a separate change.

Implements RETURNING for insert with executemany

Adds support to return_defaults() mode and inserted_primary_key
to support mutiple INSERTed rows, via return_defauls_rows
and inserted_primary_key_rows accessors.

within default execution context, new cached compiler
getters are used to fetch primary keys from rows

inserted_primary_key now returns a plain tuple. this
is not yet a row-like object however this can be
added.

Adds distinct "values_only" and "batch" modes, as
"values" has a lot of benefits but "batch" breaks
cursor.rowcount

psycopg2 minimum version 2.7 so we can remove the
large number of checks for very old versions of
psycopg2

simplify tests to no longer distinguish between
native and non-native json

Fixes: #5401
Change-Id: Ic08fd3423d4c5d16ca50994460c0c234868bd61c

1 files changed, 26 insertions, 10 deletions

diff --git a/lib/sqlalchemy/sql/dml.py b/lib/sqlalchemy/sql/dml.py
index 50b2a935a..4e8430450 100644
--- a/lib/sqlalchemy/sql/dml.py
+++ b/lib/sqlalchemy/sql/dml.py
@@ -693,18 +693,18 @@ class ValuesBase(UpdateBase):
 
         This method differs from :meth:`.UpdateBase.returning` in these ways:
 
-        1. :meth:`.ValuesBase.return_defaults` is only intended for use with
-           an INSERT or an UPDATE statement that matches exactly one row.
-           While the RETURNING construct in the general sense supports
-           multiple rows for a multi-row UPDATE or DELETE statement, or for
-           special cases of INSERT that return multiple rows (e.g. INSERT from
-           SELECT, multi-valued VALUES clause),
+        1. :meth:`.ValuesBase.return_defaults` is only intended for use with an
+           INSERT or an UPDATE statement that matches exactly one row per
+           parameter set. While the RETURNING construct in the general sense
+           supports multiple rows for a multi-row UPDATE or DELETE statement,
+           or for special cases of INSERT that return multiple rows (e.g.
+           INSERT from SELECT, multi-valued VALUES clause),
            :meth:`.ValuesBase.return_defaults` is intended only for an
-           "ORM-style" single-row INSERT/UPDATE statement.  The row returned
-           by the statement is also consumed implicitly when
+           "ORM-style" single-row INSERT/UPDATE statement.  The row
+           returned by the statement is also consumed implicitly when
            :meth:`.ValuesBase.return_defaults` is used.  By contrast,
-           :meth:`.UpdateBase.returning` leaves the RETURNING result-set
-           intact with a collection of any number of rows.
+           :meth:`.UpdateBase.returning` leaves the RETURNING result-set intact
+           with a collection of any number of rows.
 
         2. It is compatible with the existing logic to fetch auto-generated
            primary key values, also known as "implicit returning".  Backends
@@ -718,6 +718,16 @@ class ValuesBase(UpdateBase):
            an exception.  The return value of
            :attr:`_engine.CursorResult.returned_defaults` will be ``None``
 
+        4. An INSERT statement invoked with executemany() is supported if the
+           backend database driver supports the
+           ``insert_executemany_returning`` feature, currently this includes
+           PostgreSQL with psycopg2.  When executemany is used, the
+           :attr:`_engine.CursorResult.returned_defaults_rows` and
+           :attr:`_engine.CursorResult.inserted_primary_key_rows` accessors
+           will return the inserted defaults and primary keys.
+
+           .. versionadded:: 1.4
+
         :meth:`.ValuesBase.return_defaults` is used by the ORM to provide
         an efficient implementation for the ``eager_defaults`` feature of
         :func:`.mapper`.
@@ -735,6 +745,12 @@ class ValuesBase(UpdateBase):
 
             :attr:`_engine.CursorResult.returned_defaults`
 
+            :attr:`_engine.CursorResult.returned_defaults_rows`
+
+            :attr:`_engine.CursorResult.inserted_primary_key`
+
+            :attr:`_engine.CursorResult.inserted_primary_key_rows`
+
         """
         self._return_defaults = cols or True