- Remove deprecated method ``get_primary_keys` in the :class:`.Dialect` and
  :class:`.Inspector` classes.
- Remove deprecated event ``dbapi_error`` and the method ``ConnectionEvents.dbapi_error`.
- Remove support for deprecated engine URLs of the form ``postgres://``.
- Remove deprecated dialect ``mysql+gaerdbms``.
- Remove deprecated parameter ``quoting`` from :class:`.mysql.ENUM`
  and :class:`.mysql.SET` in the ``mysql`` dialect.
- Remove deprecated function ``comparable_property``. and function
  ``comparable_using`` in the declarative extension.
- Remove deprecated function ``compile_mappers``.
- Remove deprecated method ``collection.linker``.
- Remove deprecated method ``Session.prune`` and parameter ``Session.weak_identity_map``.
  This change also removes the class ``StrongInstanceDict``.
- Remove deprecated parameter ``mapper.order_by``.
- Remove deprecated parameter ``Session._enable_transaction_accounting`.
- Remove deprecated parameter ``Session.is_modified.passive``.
- Remove deprecated class ``Binary``. Please use :class:`.LargeBinary`.
- Remove deprecated methods ``Compiled.compile``, ``ClauseElement.__and__`` and
  ``ClauseElement.__or__`` and attribute ``Over.func``.
- Remove deprecated ``FromClause.count`` method.
- Remove deprecated parameter ``Table.useexisting``.
- Remove deprecated parameters ``text.bindparams`` and ``text.typemap``.

- Remove boolean support for the ``passive`` parameter in ``get_history``.
- Remove deprecated ``adapt_operator`` in ``UserDefinedType.Comparator``.

Fixes: #4643
Change-Id: Idcd390c77bf7b0e9957907716993bdaa3f1a1763

The "autoflush" behavior of :class:`.Query` will now trigger for nearly
all ORM level attribute load operations, including when a deferred
column is loaded as well as when an expired column is loaded.   Previously,
autoflush on load of expired or unloaded attributes was limited to
relationship-bound attributes only.   However, this led to the issue
where column-based attributes that also depended on other rows, or even
other columns in the same row, in order to express the correct value,
would show an effectively stale value when accessed as there could be
pending changes in the session left to be flushed.    Autoflush
is now disabled only in some cases where attributes are being unexpired in
the context of a history operation.

Fixes: #5226
Change-Id: Ibd965b30918cd273ae020411a704bf2bb1891f59

Added "raiseload" feature for ORM mapped columns.

As part of this change, the behavior of "deferred" is now more strict;
an attribute that is set up as "deferred" at the mapper level no longer
participates in an "unexpire" operation; that is, when an unexpire loads
all the expired columns of an object which are not themselves in a deferred
group, those which are mapper-level deferred will never be loaded.

Deferral options set at query time should always be reset by an expiration
operation.

Renames deferred_scalar_loader to expired_attribute_loader

Unfortunately we can't have raiseload() do this because it would break
existing wildcard behavior.

Fixes: #4826
Change-Id: I30d9a30236e0b69134e4094fb7c1ad2267f089d1

Fixed regression in selectinload loader strategy caused by #4775 (released
in version 1.3.6) where a many-to-one attribute of None would no longer be
populated by the loader.  While this was usually not noticeable due to the
lazyloader populating None upon get, it would lead to a detached instance
error if the object were detached.

Fixes: #4872
Change-Id: I18466841683111643810ebc4331376df38c4767b

A bulk replace operation was not attending to the previous
list still present in the "_empty_collections" dictionary
which was added as part of #4519.

Fixes: #4519
Change-Id: I3f99f8647c0fb8140b3dfb03686a5d3b90da633f

This is a very useful assertion which prevents unused variables
from being set up allows code to be more readable and sometimes
even more efficient.  test suites seem to be where the most
problems are and there do not seem to be documentation examples
that are using this, or at least the linter is not taking effect
within rst blocks.

Change-Id: I2b3341d8dd14da34879d8425838e66a4b9f8e27d

Accessing a collection-oriented attribute on a newly created object no
longer mutates ``__dict__``, but still returns an empty collection as has
always been the case.   This allows collection-oriented attributes to work
consistently in comparison to scalar attributes which return ``None``, but
also don't mutate ``__dict__``.  In order to accommodate for the collection
being mutated, the same empty collection is returned each time once
initially created, and when it is mutated (e.g. an item appended, added,
etc.) it is then moved into ``__dict__``.  This removes the last of
mutating side-effects on read-only attribute access within the ORM.

Fixes: #4519
Change-Id: I06a058d24e6eb24b5c6b6092d3f8b31cf9c244ae

There's no real difference between these two constants
except they are used in different places and therefore allow
various codepaths to work largely by accident.   These
codepaths should be explicit.   Assign NO_VALUE and NEVER_SET
to the same constant and work towards having just one constant
for "we have no value to return right now".

Fixes: #4696
Change-Id: I7c324967952c1886bf202074d627323a2ad013cc

Fixed issue where the :paramref:`.AttributeEvents.active_history` flag
would not be set for an event listener that propgated to a subclass via the
:paramref:`.AttributeEvents.propagate` flag.   This bug has been present
for the full span of the :class:`.AttributeEvents` system.

Fixes: #4695
Change-Id: Ie384f4847f37c267d94b6d56e7538438efc1a54c

A large change throughout the library has ensured that all objects, parameters,
and behaviors which have been noted as deprecated or legacy now emit
``DeprecationWarning`` warnings when invoked.   As the Python 3 interpreter now
defaults to displaying deprecation warnings, as well as that modern test suites
based on tools like tox and pytest tend to display deprecation warnings,
this change should make it easier to note what API features are obsolete.

See the notes added to the changelog and migration notes for further
details.

Fixes: #4393
Change-Id: If0ea11a1fc24f9a8029352eeadfc49a7a54c0a1b