Fixed regression caused by :ticket:`2677` whereby calling
:meth:`.Session.delete` on an object that was already flushed as
deleted in that session would fail to set up the object in the
identity map (or reject the object), causing flush errors as the
object were in a state not accommodated by the unit of work.
The pre-1.1 behavior in this case has been restored, which is that
the object is put back into the identity map so that the DELETE
statement will be attempted again, which emits a warning that the number
of expected rows was not matched (unless the row were restored outside
of the session).

Change-Id: I9a8871f82cb1ebe67a7ad54d888d5ee835a9a40a
Fixes: #3839

Add checks in spots where state.obj() might be late-GC'ed before
we get a chance to call the event.   There may be more cases
of these which we should address as they come up.  The Session
should always be maintaining strong refs to objects that have
pending operations left on them, so for these cases we need
to ensure that ref remains long enough for the event to be called.

Change-Id: I1a7c7bc57130acc11f54ad55924af2e36ac75101
Fixes: #3808

and nested attributes and what these mean
- improve linking for after_transaction_create() / after_transaction_end()
events
- add public .parent attribute to detect top-level transaction within
these events

Change-Id: Ie7382bc8fe5de226160dcb6a5019e19fcc5af38e

Fixes: #3798
Change-Id: Ib4e6344b599e871f9d46d36a5aeb7ba3104dc99b
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/293

Currently, ``Session.bulk_insert_mappings`` omits NULL values which
causes it to break up batches of inserts based on which batches
contain NULL and which do not.

By adding this flag, the same columns are rendered in the INSERT
for all rows allowing them to be batched.  The downside is that
server-side defaults are omitted.

Doctext-author: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: Iec5969304d4bdbf57290b200331bde02254aa3a5
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/243

fixes #3488

Change-Id: Ic9577b800e4a4e2465ec7f3a2e95bd231f5337ee
Co-Authored-By: Mike Bayer <mike_mp@zzzcomputing.com>

a savepoint being cancelled first covered in :ticket:`2696`,
the failure mode in which the :class:`.Session` is placed when a
SAVEPOINT vanishes before rollback has been improved to allow the
:class:`.Session` to still function outside of that savepoint.
It is assumed that the savepoint operation failed and was cancelled.
fixes #3680

primary key that has values for some but not all of the PK fields
would emit a SELECT statement leaking the internal NEVER_SET symbol
into the query, rather than detecting that this object does not have
a searchable primary key and no SELECT should be emitted.
fixes #3647

- establish make_transient and make_transient_to_detached as special-use,
advanced use only functions
- list all conditions under make_transient() under which an attribute
will not be loaded and establish that make_transient() does not attempt
to load all attributes before detaching the object from its
session, fixes #3640