a much more modest outcome than what we started with. The
work of create_row_processor() for ColumnProperty objects
is essentially done at query setup time combined with some
lookups in _instance_processor().
- to allow this change for deferred columns, deferred columns
no longer search for themselves in the result. If they've been
set up as deferred without any explicit directive to undefer them,
then this is what was asked for. if we don't do this,
then we're stuck with this performance penalty for all deferred
columns which in the vast majority of typical use cases (e.g. loading
large, legacy tables or tables with many/large very seldom
used values) won't be present in the result and won't be accessed at all.
the :func:`.orm.load_only` option to cover all attributes not
explicitly mentioned, now takes into account the superclasses
of a given entity, if that entity is mapped with inheritance mapping,
so that attribute names within the superclasses are also omitted
from the load. Additionally, the polymorphic discriminator column
is unconditionally included in the list, just in the same way that
primary key columns are, so that even with load_only() set up,
polymorphic loading of subtypes continues to function correctly.
fixes#3287
columns are always added to the list of columns to be "undeferred";
otherwise, the ORM can't load the row's identity. Apparently,
one can defer the mapped primary keys and the ORM will fail, that
hasn't been changed. But as load_only is essentially saying
"defer all but X", it's more critical that PK cols not be part of this
deferral. fixes#3080
- 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.
Mike Bayer