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# Copyright (C) 2005-2016 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""
"""
from .interfaces import MapperOption, PropComparator
from .. import util
from ..sql.base import _generative, Generative
from .. import exc as sa_exc, inspect
from .base import _is_aliased_class, _class_to_mapper
from . import util as orm_util
from .path_registry import PathRegistry, TokenRegistry, \
_WILDCARD_TOKEN, _DEFAULT_TOKEN
class Load(Generative, MapperOption):
"""Represents loader options which modify the state of a
:class:`.Query` in order to affect how various mapped attributes are
loaded.
.. versionadded:: 0.9.0 The :meth:`.Load` system is a new foundation for
the existing system of loader options, including options such as
:func:`.orm.joinedload`, :func:`.orm.defer`, and others. In
particular, it introduces a new method-chained system that replaces the
need for dot-separated paths as well as "_all()" options such as
:func:`.orm.joinedload_all`.
A :class:`.Load` object can be used directly or indirectly. To use one
directly, instantiate given the parent class. This style of usage is
useful when dealing with a :class:`.Query` that has multiple entities,
or when producing a loader option that can be applied generically to
any style of query::
myopt = Load(MyClass).joinedload("widgets")
The above ``myopt`` can now be used with :meth:`.Query.options`::
session.query(MyClass).options(myopt)
The :class:`.Load` construct is invoked indirectly whenever one makes use
of the various loader options that are present in ``sqlalchemy.orm``,
including options such as :func:`.orm.joinedload`, :func:`.orm.defer`,
:func:`.orm.subqueryload`, and all the rest. These constructs produce an
"anonymous" form of the :class:`.Load` object which tracks attributes and
options, but is not linked to a parent class until it is associated with a
parent :class:`.Query`::
# produce "unbound" Load object
myopt = joinedload("widgets")
# when applied using options(), the option is "bound" to the
# class observed in the given query, e.g. MyClass
session.query(MyClass).options(myopt)
Whether the direct or indirect style is used, the :class:`.Load` object
returned now represents a specific "path" along the entities of a
:class:`.Query`. This path can be traversed using a standard
method-chaining approach. Supposing a class hierarchy such as ``User``,
``User.addresses -> Address``, ``User.orders -> Order`` and
``Order.items -> Item``, we can specify a variety of loader options along
each element in the "path"::
session.query(User).options(
joinedload("addresses"),
subqueryload("orders").joinedload("items")
)
Where above, the ``addresses`` collection will be joined-loaded, the
``orders`` collection will be subquery-loaded, and within that subquery
load the ``items`` collection will be joined-loaded.
"""
def __init__(self, entity):
insp = inspect(entity)
self.path = insp._path_registry
self.context = {}
self.local_opts = {}
def _generate(self):
cloned = super(Load, self)._generate()
cloned.local_opts = {}
return cloned
_merge_into_path = False
strategy = None
propagate_to_loaders = False
def process_query(self, query):
self._process(query, True)
def process_query_conditionally(self, query):
self._process(query, False)
def _process(self, query, raiseerr):
current_path = query._current_path
if current_path:
for (token, start_path), loader in self.context.items():
chopped_start_path = self._chop_path(start_path, current_path)
if chopped_start_path is not None:
query._attributes[(token, chopped_start_path)] = loader
else:
query._attributes.update(self.context)
def _generate_path(self, path, attr, wildcard_key, raiseerr=True):
if raiseerr and not path.has_entity:
if isinstance(path, TokenRegistry):
raise sa_exc.ArgumentError(
"Wildcard token cannot be followed by another entity")
else:
raise sa_exc.ArgumentError(
"Attribute '%s' of entity '%s' does not "
"refer to a mapped entity" %
(path.prop.key, path.parent.entity)
)
if isinstance(attr, util.string_types):
default_token = attr.endswith(_DEFAULT_TOKEN)
if attr.endswith(_WILDCARD_TOKEN) or default_token:
if default_token:
self.propagate_to_loaders = False
if wildcard_key:
attr = "%s:%s" % (wildcard_key, attr)
return path.token(attr)
try:
# use getattr on the class to work around
# synonyms, hybrids, etc.
attr = getattr(path.entity.class_, attr)
except AttributeError:
if raiseerr:
raise sa_exc.ArgumentError(
"Can't find property named '%s' on the "
"mapped entity %s in this Query. " % (
attr, path.entity)
)
else:
return None
else:
attr = attr.property
path = path[attr]
else:
prop = attr.property
if not prop.parent.common_parent(path.mapper):
if raiseerr:
raise sa_exc.ArgumentError(
"Attribute '%s' does not "
"link from element '%s'" % (attr, path.entity))
else:
return None
if getattr(attr, '_of_type', None):
ac = attr._of_type
ext_info = inspect(ac)
path_element = ext_info.mapper
existing = path.entity_path[prop].get(
self.context, "path_with_polymorphic")
if not ext_info.is_aliased_class:
ac = orm_util.with_polymorphic(
ext_info.mapper.base_mapper,
ext_info.mapper, aliased=True,
_use_mapper_path=True,
_existing_alias=existing)
path.entity_path[prop].set(
self.context, "path_with_polymorphic", inspect(ac))
path = path[prop][path_element]
else:
path = path[prop]
if path.has_entity:
path = path.entity_path
return path
def __str__(self):
return "Load(strategy=%r)" % (self.strategy, )
def _coerce_strat(self, strategy):
if strategy is not None:
strategy = tuple(sorted(strategy.items()))
return strategy
@_generative
def set_relationship_strategy(
self, attr, strategy, propagate_to_loaders=True):
strategy = self._coerce_strat(strategy)
self.propagate_to_loaders = propagate_to_loaders
# if the path is a wildcard, this will set propagate_to_loaders=False
self.path = self._generate_path(self.path, attr, "relationship")
self.strategy = strategy
if strategy is not None:
self._set_path_strategy()
@_generative
def set_column_strategy(self, attrs, strategy, opts=None):
strategy = self._coerce_strat(strategy)
for attr in attrs:
path = self._generate_path(self.path, attr, "column")
cloned = self._generate()
cloned.strategy = strategy
cloned.path = path
cloned.propagate_to_loaders = True
if opts:
cloned.local_opts.update(opts)
cloned._set_path_strategy()
def _set_path_strategy(self):
if self._merge_into_path:
# special helper for undefer_group
existing = self.path.get(self.context, "loader")
if existing:
existing.local_opts.update(self.local_opts)
else:
self.path.set(self.context, "loader", self)
elif self.path.has_entity:
self.path.parent.set(self.context, "loader", self)
else:
self.path.set(self.context, "loader", self)
def __getstate__(self):
d = self.__dict__.copy()
d["path"] = self.path.serialize()
return d
def __setstate__(self, state):
self.__dict__.update(state)
self.path = PathRegistry.deserialize(self.path)
def _chop_path(self, to_chop, path):
i = -1
for i, (c_token, p_token) in enumerate(zip(to_chop, path.path)):
if isinstance(c_token, util.string_types):
# TODO: this is approximated from the _UnboundLoad
# version and probably has issues, not fully covered.
if i == 0 and c_token.endswith(':' + _DEFAULT_TOKEN):
return to_chop
elif c_token != 'relationship:%s' % (_WILDCARD_TOKEN,) and \
c_token != p_token.key:
return None
if c_token is p_token:
continue
else:
return None
return to_chop[i + 1:]
class _UnboundLoad(Load):
"""Represent a loader option that isn't tied to a root entity.
The loader option will produce an entity-linked :class:`.Load`
object when it is passed :meth:`.Query.options`.
This provides compatibility with the traditional system
of freestanding options, e.g. ``joinedload('x.y.z')``.
"""
def __init__(self):
self.path = ()
self._to_bind = set()
self.local_opts = {}
_is_chain_link = False
def _set_path_strategy(self):
self._to_bind.add(self)
def _generate_path(self, path, attr, wildcard_key):
if wildcard_key and isinstance(attr, util.string_types) and \
attr in (_WILDCARD_TOKEN, _DEFAULT_TOKEN):
if attr == _DEFAULT_TOKEN:
self.propagate_to_loaders = False
attr = "%s:%s" % (wildcard_key, attr)
return path + (attr, )
def __getstate__(self):
d = self.__dict__.copy()
d['path'] = ret = []
for token in util.to_list(self.path):
if isinstance(token, PropComparator):
ret.append((token._parentmapper.class_, token.key))
else:
ret.append(token)
return d
def __setstate__(self, state):
ret = []
for key in state['path']:
if isinstance(key, tuple):
cls, propkey = key
ret.append(getattr(cls, propkey))
else:
ret.append(key)
state['path'] = tuple(ret)
self.__dict__ = state
def _process(self, query, raiseerr):
for val in self._to_bind:
val._bind_loader(query, query._attributes, raiseerr)
@classmethod
def _from_keys(self, meth, keys, chained, kw):
opt = _UnboundLoad()
def _split_key(key):
if isinstance(key, util.string_types):
# coerce fooload('*') into "default loader strategy"
if key == _WILDCARD_TOKEN:
return (_DEFAULT_TOKEN, )
# coerce fooload(".*") into "wildcard on default entity"
elif key.startswith("." + _WILDCARD_TOKEN):
key = key[1:]
return key.split(".")
else:
return (key,)
all_tokens = [token for key in keys for token in _split_key(key)]
for token in all_tokens[0:-1]:
if chained:
opt = meth(opt, token, **kw)
else:
opt = opt.defaultload(token)
opt._is_chain_link = True
opt = meth(opt, all_tokens[-1], **kw)
opt._is_chain_link = False
return opt
def _chop_path(self, to_chop, path):
i = -1
for i, (c_token, (p_mapper, p_prop)) in enumerate(
zip(to_chop, path.pairs())):
if isinstance(c_token, util.string_types):
if i == 0 and c_token.endswith(':' + _DEFAULT_TOKEN):
return to_chop
elif c_token != 'relationship:%s' % (
_WILDCARD_TOKEN,) and c_token != p_prop.key:
return None
elif isinstance(c_token, PropComparator):
if c_token.property is not p_prop:
return None
else:
i += 1
return to_chop[i:]
def _bind_loader(self, query, context, raiseerr):
start_path = self.path
# _current_path implies we're in a
# secondary load with an existing path
current_path = query._current_path
if current_path:
start_path = self._chop_path(start_path, current_path)
if not start_path:
return None
token = start_path[0]
if isinstance(token, util.string_types):
entity = self._find_entity_basestring(query, token, raiseerr)
elif isinstance(token, PropComparator):
prop = token.property
entity = self._find_entity_prop_comparator(
query,
prop.key,
token._parententity,
raiseerr)
else:
raise sa_exc.ArgumentError(
"mapper option expects "
"string key or list of attributes")
if not entity:
return
path_element = entity.entity_zero
# transfer our entity-less state into a Load() object
# with a real entity path.
loader = Load(path_element)
loader.context = context
loader.strategy = self.strategy
path = loader.path
for token in start_path:
loader.path = path = loader._generate_path(
loader.path, token, None, raiseerr)
if path is None:
return
loader.local_opts.update(self.local_opts)
if loader.path.has_entity:
effective_path = loader.path.parent
else:
effective_path = loader.path
# prioritize "first class" options over those
# that were "links in the chain", e.g. "x" and "y" in
# someload("x.y.z") versus someload("x") / someload("x.y")
if effective_path.is_token:
for path in effective_path.generate_for_superclasses():
if self._merge_into_path:
# special helper for undefer_group
existing = path.get(context, "loader")
if existing:
existing.local_opts.update(self.local_opts)
else:
path.set(context, "loader", loader)
elif self._is_chain_link:
path.setdefault(context, "loader", loader)
else:
path.set(context, "loader", loader)
else:
# only supported for the undefer_group() wildcard opt
assert not self._merge_into_path
if self._is_chain_link:
effective_path.setdefault(context, "loader", loader)
else:
effective_path.set(context, "loader", loader)
def _find_entity_prop_comparator(self, query, token, mapper, raiseerr):
if _is_aliased_class(mapper):
searchfor = mapper
else:
searchfor = _class_to_mapper(mapper)
for ent in query._mapper_entities:
if ent.corresponds_to(searchfor):
return ent
else:
if raiseerr:
if not list(query._mapper_entities):
raise sa_exc.ArgumentError(
"Query has only expression-based entities - "
"can't find property named '%s'."
% (token, )
)
else:
raise sa_exc.ArgumentError(
"Can't find property '%s' on any entity "
"specified in this Query. Note the full path "
"from root (%s) to target entity must be specified."
% (token, ",".join(str(x) for
x in query._mapper_entities))
)
else:
return None
def _find_entity_basestring(self, query, token, raiseerr):
if token.endswith(':' + _WILDCARD_TOKEN):
if len(list(query._mapper_entities)) != 1:
if raiseerr:
raise sa_exc.ArgumentError(
"Wildcard loader can only be used with exactly "
"one entity. Use Load(ent) to specify "
"specific entities.")
elif token.endswith(_DEFAULT_TOKEN):
raiseerr = False
for ent in query._mapper_entities:
# return only the first _MapperEntity when searching
# based on string prop name. Ideally object
# attributes are used to specify more exactly.
return ent
else:
if raiseerr:
raise sa_exc.ArgumentError(
"Query has only expression-based entities - "
"can't find property named '%s'."
% (token, )
)
else:
return None
class loader_option(object):
def __init__(self):
pass
def __call__(self, fn):
self.name = name = fn.__name__
self.fn = fn
if hasattr(Load, name):
raise TypeError("Load class already has a %s method." % (name))
setattr(Load, name, fn)
return self
def _add_unbound_fn(self, fn):
self._unbound_fn = fn
fn_doc = self.fn.__doc__
self.fn.__doc__ = """Produce a new :class:`.Load` object with the
:func:`.orm.%(name)s` option applied.
See :func:`.orm.%(name)s` for usage examples.
""" % {"name": self.name}
fn.__doc__ = fn_doc
return self
def _add_unbound_all_fn(self, fn):
self._unbound_all_fn = fn
fn.__doc__ = """Produce a standalone "all" option for :func:`.orm.%(name)s`.
.. deprecated:: 0.9.0
The "_all()" style is replaced by method chaining, e.g.::
session.query(MyClass).options(
%(name)s("someattribute").%(name)s("anotherattribute")
)
""" % {"name": self.name}
return self
@loader_option()
def contains_eager(loadopt, attr, alias=None):
"""Indicate that the given attribute should be eagerly loaded from
columns stated manually in the query.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
The option is used in conjunction with an explicit join that loads
the desired rows, i.e.::
sess.query(Order).\\
join(Order.user).\\
options(contains_eager(Order.user))
The above query would join from the ``Order`` entity to its related
``User`` entity, and the returned ``Order`` objects would have the
``Order.user`` attribute pre-populated.
:func:`contains_eager` also accepts an `alias` argument, which is the
string name of an alias, an :func:`~sqlalchemy.sql.expression.alias`
construct, or an :func:`~sqlalchemy.orm.aliased` construct. Use this when
the eagerly-loaded rows are to come from an aliased table::
user_alias = aliased(User)
sess.query(Order).\\
join((user_alias, Order.user)).\\
options(contains_eager(Order.user, alias=user_alias))
.. seealso::
:ref:`contains_eager`
"""
if alias is not None:
if not isinstance(alias, str):
info = inspect(alias)
alias = info.selectable
cloned = loadopt.set_relationship_strategy(
attr,
{"lazy": "joined"},
propagate_to_loaders=False
)
cloned.local_opts['eager_from_alias'] = alias
return cloned
@contains_eager._add_unbound_fn
def contains_eager(*keys, **kw):
return _UnboundLoad()._from_keys(
_UnboundLoad.contains_eager, keys, True, kw)
@loader_option()
def load_only(loadopt, *attrs):
"""Indicate that for a particular entity, only the given list
of column-based attribute names should be loaded; all others will be
deferred.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
Example - given a class ``User``, load only the ``name`` and ``fullname``
attributes::
session.query(User).options(load_only("name", "fullname"))
Example - given a relationship ``User.addresses -> Address``, specify
subquery loading for the ``User.addresses`` collection, but on each
``Address`` object load only the ``email_address`` attribute::
session.query(User).options(
subqueryload("addresses").load_only("email_address")
)
For a :class:`.Query` that has multiple entities, the lead entity can be
specifically referred to using the :class:`.Load` constructor::
session.query(User, Address).join(User.addresses).options(
Load(User).load_only("name", "fullname"),
Load(Address).load_only("email_addres")
)
.. versionadded:: 0.9.0
"""
cloned = loadopt.set_column_strategy(
attrs,
{"deferred": False, "instrument": True}
)
cloned.set_column_strategy("*",
{"deferred": True, "instrument": True},
{"undefer_pks": True})
return cloned
@load_only._add_unbound_fn
def load_only(*attrs):
return _UnboundLoad().load_only(*attrs)
@loader_option()
def joinedload(loadopt, attr, innerjoin=None):
"""Indicate that the given attribute should be loaded using joined
eager loading.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
examples::
# joined-load the "orders" collection on "User"
query(User).options(joinedload(User.orders))
# joined-load Order.items and then Item.keywords
query(Order).options(joinedload(Order.items).joinedload(Item.keywords))
# lazily load Order.items, but when Items are loaded,
# joined-load the keywords collection
query(Order).options(lazyload(Order.items).joinedload(Item.keywords))
:param innerjoin: if ``True``, indicates that the joined eager load should
use an inner join instead of the default of left outer join::
query(Order).options(joinedload(Order.user, innerjoin=True))
In order to chain multiple eager joins together where some may be
OUTER and others INNER, right-nested joins are used to link them::
query(A).options(
joinedload(A.bs, innerjoin=False).
joinedload(B.cs, innerjoin=True)
)
The above query, linking A.bs via "outer" join and B.cs via "inner" join
would render the joins as "a LEFT OUTER JOIN (b JOIN c)". When using
SQLite, this form of JOIN is translated to use full subqueries as this
syntax is otherwise not directly supported.
The ``innerjoin`` flag can also be stated with the term ``"unnested"``.
This will prevent joins from being right-nested, and will instead
link an "innerjoin" eagerload to an "outerjoin" eagerload by bypassing
the "inner" join. Using this form as follows::
query(A).options(
joinedload(A.bs, innerjoin=False).
joinedload(B.cs, innerjoin="unnested")
)
Joins will be rendered as "a LEFT OUTER JOIN b LEFT OUTER JOIN c", so that
all of "a" is matched rather than being incorrectly limited by a "b" that
does not contain a "c".
.. note:: The "unnested" flag does **not** affect the JOIN rendered
from a many-to-many association table, e.g. a table configured
as :paramref:`.relationship.secondary`, to the target table; for
correctness of results, these joins are always INNER and are
therefore right-nested if linked to an OUTER join.
.. versionadded:: 0.9.4 Added support for "nesting" of eager "inner"
joins. See :ref:`feature_2976`.
.. versionchanged:: 1.0.0 ``innerjoin=True`` now implies
``innerjoin="nested"``, whereas in 0.9 it implied
``innerjoin="unnested"``. In order to achieve the pre-1.0 "unnested"
inner join behavior, use the value ``innerjoin="unnested"``.
See :ref:`migration_3008`.
.. note::
The joins produced by :func:`.orm.joinedload` are **anonymously
aliased**. The criteria by which the join proceeds cannot be
modified, nor can the :class:`.Query` refer to these joins in any way,
including ordering.
To produce a specific SQL JOIN which is explicitly available, use
:meth:`.Query.join`. To combine explicit JOINs with eager loading
of collections, use :func:`.orm.contains_eager`; see
:ref:`contains_eager`.
.. seealso::
:ref:`loading_toplevel`
:ref:`contains_eager`
:func:`.orm.subqueryload`
:func:`.orm.lazyload`
:paramref:`.relationship.lazy`
:paramref:`.relationship.innerjoin` - :func:`.relationship`-level
version of the :paramref:`.joinedload.innerjoin` option.
"""
loader = loadopt.set_relationship_strategy(attr, {"lazy": "joined"})
if innerjoin is not None:
loader.local_opts['innerjoin'] = innerjoin
return loader
@joinedload._add_unbound_fn
def joinedload(*keys, **kw):
return _UnboundLoad._from_keys(
_UnboundLoad.joinedload, keys, False, kw)
@joinedload._add_unbound_all_fn
def joinedload_all(*keys, **kw):
return _UnboundLoad._from_keys(
_UnboundLoad.joinedload, keys, True, kw)
@loader_option()
def subqueryload(loadopt, attr):
"""Indicate that the given attribute should be loaded using
subquery eager loading.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
examples::
# subquery-load the "orders" collection on "User"
query(User).options(subqueryload(User.orders))
# subquery-load Order.items and then Item.keywords
query(Order).options(subqueryload(Order.items).subqueryload(Item.keywords))
# lazily load Order.items, but when Items are loaded,
# subquery-load the keywords collection
query(Order).options(lazyload(Order.items).subqueryload(Item.keywords))
.. seealso::
:ref:`loading_toplevel`
:func:`.orm.joinedload`
:func:`.orm.lazyload`
:paramref:`.relationship.lazy`
"""
return loadopt.set_relationship_strategy(attr, {"lazy": "subquery"})
@subqueryload._add_unbound_fn
def subqueryload(*keys):
return _UnboundLoad._from_keys(_UnboundLoad.subqueryload, keys, False, {})
@subqueryload._add_unbound_all_fn
def subqueryload_all(*keys):
return _UnboundLoad._from_keys(_UnboundLoad.subqueryload, keys, True, {})
@loader_option()
def lazyload(loadopt, attr):
"""Indicate that the given attribute should be loaded using "lazy"
loading.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
.. seealso::
:paramref:`.relationship.lazy`
"""
return loadopt.set_relationship_strategy(attr, {"lazy": "select"})
@lazyload._add_unbound_fn
def lazyload(*keys):
return _UnboundLoad._from_keys(_UnboundLoad.lazyload, keys, False, {})
@lazyload._add_unbound_all_fn
def lazyload_all(*keys):
return _UnboundLoad._from_keys(_UnboundLoad.lazyload, keys, True, {})
@loader_option()
def immediateload(loadopt, attr):
"""Indicate that the given attribute should be loaded using
an immediate load with a per-attribute SELECT statement.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
.. seealso::
:ref:`loading_toplevel`
:func:`.orm.joinedload`
:func:`.orm.lazyload`
:paramref:`.relationship.lazy`
"""
loader = loadopt.set_relationship_strategy(attr, {"lazy": "immediate"})
return loader
@immediateload._add_unbound_fn
def immediateload(*keys):
return _UnboundLoad._from_keys(
_UnboundLoad.immediateload, keys, False, {})
@loader_option()
def noload(loadopt, attr):
"""Indicate that the given relationship attribute should remain unloaded.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
:func:`.orm.noload` applies to :func:`.relationship` attributes; for
column-based attributes, see :func:`.orm.defer`.
"""
return loadopt.set_relationship_strategy(attr, {"lazy": "noload"})
@noload._add_unbound_fn
def noload(*keys):
return _UnboundLoad._from_keys(_UnboundLoad.noload, keys, False, {})
@loader_option()
def defaultload(loadopt, attr):
"""Indicate an attribute should load using its default loader style.
This method is used to link to other loader options, such as
to set the :func:`.orm.defer` option on a class that is linked to
a relationship of the parent class being loaded, :func:`.orm.defaultload`
can be used to navigate this path without changing the loading style
of the relationship::
session.query(MyClass).options(defaultload("someattr").defer("some_column"))
.. seealso::
:func:`.orm.defer`
:func:`.orm.undefer`
"""
return loadopt.set_relationship_strategy(
attr,
None
)
@defaultload._add_unbound_fn
def defaultload(*keys):
return _UnboundLoad._from_keys(_UnboundLoad.defaultload, keys, False, {})
@loader_option()
def defer(loadopt, key):
"""Indicate that the given column-oriented attribute should be deferred, e.g.
not loaded until accessed.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
e.g.::
from sqlalchemy.orm import defer
session.query(MyClass).options(
defer("attribute_one"),
defer("attribute_two"))
session.query(MyClass).options(
defer(MyClass.attribute_one),
defer(MyClass.attribute_two))
To specify a deferred load of an attribute on a related class,
the path can be specified one token at a time, specifying the loading
style for each link along the chain. To leave the loading style
for a link unchanged, use :func:`.orm.defaultload`::
session.query(MyClass).options(defaultload("someattr").defer("some_column"))
A :class:`.Load` object that is present on a certain path can have
:meth:`.Load.defer` called multiple times, each will operate on the same
parent entity::
session.query(MyClass).options(
defaultload("someattr").
defer("some_column").
defer("some_other_column").
defer("another_column")
)
:param key: Attribute to be deferred.
:param \*addl_attrs: Deprecated; this option supports the old 0.8 style
of specifying a path as a series of attributes, which is now superseded
by the method-chained style.
.. seealso::
:ref:`deferred`
:func:`.orm.undefer`
"""
return loadopt.set_column_strategy(
(key, ),
{"deferred": True, "instrument": True}
)
@defer._add_unbound_fn
def defer(key, *addl_attrs):
return _UnboundLoad._from_keys(
_UnboundLoad.defer, (key, ) + addl_attrs, False, {})
@loader_option()
def undefer(loadopt, key):
"""Indicate that the given column-oriented attribute should be undeferred,
e.g. specified within the SELECT statement of the entity as a whole.
The column being undeferred is typically set up on the mapping as a
:func:`.deferred` attribute.
This function is part of the :class:`.Load` interface and supports
both method-chained and standalone operation.
Examples::
# undefer two columns
session.query(MyClass).options(undefer("col1"), undefer("col2"))
# undefer all columns specific to a single class using Load + *
session.query(MyClass, MyOtherClass).options(
Load(MyClass).undefer("*"))
:param key: Attribute to be undeferred.
:param \*addl_attrs: Deprecated; this option supports the old 0.8 style
of specifying a path as a series of attributes, which is now superseded
by the method-chained style.
.. seealso::
:ref:`deferred`
:func:`.orm.defer`
:func:`.orm.undefer_group`
"""
return loadopt.set_column_strategy(
(key, ),
{"deferred": False, "instrument": True}
)
@undefer._add_unbound_fn
def undefer(key, *addl_attrs):
return _UnboundLoad._from_keys(
_UnboundLoad.undefer, (key, ) + addl_attrs, False, {})
@loader_option()
def undefer_group(loadopt, name):
"""Indicate that columns within the given deferred group name should be
undeferred.
The columns being undeferred are set up on the mapping as
:func:`.deferred` attributes and include a "group" name.
E.g::
session.query(MyClass).options(undefer_group("large_attrs"))
To undefer a group of attributes on a related entity, the path can be
spelled out using relationship loader options, such as
:func:`.orm.defaultload`::
session.query(MyClass).options(
defaultload("someattr").undefer_group("large_attrs"))
.. versionchanged:: 0.9.0 :func:`.orm.undefer_group` is now specific to a
particiular entity load path.
.. seealso::
:ref:`deferred`
:func:`.orm.defer`
:func:`.orm.undefer`
"""
loadopt._merge_into_path = True
return loadopt.set_column_strategy(
"*",
None,
{"undefer_group_%s" % name: True}
)
@undefer_group._add_unbound_fn
def undefer_group(name):
return _UnboundLoad().undefer_group(name)
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