Fixes: #3512
Co-Authored-By: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: Ibd126c50eda621e2f4120ee378f7313af2d7ec3c
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/193

back_populates while still maintaining great familiarity
w/ backref so as not to confuse people.  fixes #3390

sqlalchemy/orm, sqlalchemy/event, sqlalchemy/testing

to get all flake8 passing

be used to manufacture objects that behave as though they were loaded
from a session, then detached.   Attributes that aren't present
are marked as expired, and the object can be added to a Session
where it will act like a persistent one. fix #3017

- The system of loader options has been entirely rearchitected to build
upon a much more comprehensive base, the :class:`.Load` object.  This
base allows any common loader option like :func:`.joinedload`,
:func:`.defer`, etc. to be used in a "chained" style for the purpose
of specifying options down a path, such as ``joinedload("foo").subqueryload("bar")``.
The new system supersedes the usage of dot-separated path names,
multiple attributes within options, and the usage of ``_all()`` options.
-  Added a new load option :func:`.orm.load_only`.  This allows a series
of column names to be specified as loading "only" those attributes,
deferring the rest.

of groups of column expressions to a :class:`.Query` construct.
The group of columns are returned as a single tuple by default.  The
behavior of :class:`.Bundle` can be overridden however to provide
any sort of result processing to the returned row.  One example included
is :attr:`.Composite.Comparator.bundle`, which applies a bundled form
of a "composite" mapped attribute.
[ticket:2824]
- The :func:`.composite` construct now maintains the return object
when used in a column-oriented :class:`.Query`, rather than expanding
out into individual columns.  This makes use of the new :class:`.Bundle`
feature internally.  This behavior is backwards incompatible; to
select from a composite column which will expand out, use
``MyClass.some_composite.clauses``.