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# ext/declarative/extensions.py
# Copyright (C) 2005-2024 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: https://www.opensource.org/licenses/mit-license.php
# mypy: ignore-errors
"""Public API functions and helpers for declarative."""
from __future__ import annotations
import collections
import contextlib
from typing import Any
from typing import Callable
from typing import TYPE_CHECKING
from typing import Union
from ... import exc as sa_exc
from ...engine import Connection
from ...engine import Engine
from ...orm import exc as orm_exc
from ...orm import relationships
from ...orm.base import _mapper_or_none
from ...orm.clsregistry import _resolver
from ...orm.decl_base import _DeferredMapperConfig
from ...orm.util import polymorphic_union
from ...schema import Table
from ...util import OrderedDict
if TYPE_CHECKING:
from ...sql.schema import MetaData
class ConcreteBase:
"""A helper class for 'concrete' declarative mappings.
:class:`.ConcreteBase` will use the :func:`.polymorphic_union`
function automatically, against all tables mapped as a subclass
to this class. The function is called via the
``__declare_last__()`` function, which is essentially
a hook for the :meth:`.after_configured` event.
:class:`.ConcreteBase` produces a mapped
table for the class itself. Compare to :class:`.AbstractConcreteBase`,
which does not.
Example::
from sqlalchemy.ext.declarative import ConcreteBase
class Employee(ConcreteBase, Base):
__tablename__ = 'employee'
employee_id = Column(Integer, primary_key=True)
name = Column(String(50))
__mapper_args__ = {
'polymorphic_identity':'employee',
'concrete':True}
class Manager(Employee):
__tablename__ = 'manager'
employee_id = Column(Integer, primary_key=True)
name = Column(String(50))
manager_data = Column(String(40))
__mapper_args__ = {
'polymorphic_identity':'manager',
'concrete':True}
The name of the discriminator column used by :func:`.polymorphic_union`
defaults to the name ``type``. To suit the use case of a mapping where an
actual column in a mapped table is already named ``type``, the
discriminator name can be configured by setting the
``_concrete_discriminator_name`` attribute::
class Employee(ConcreteBase, Base):
_concrete_discriminator_name = '_concrete_discriminator'
.. versionadded:: 1.3.19 Added the ``_concrete_discriminator_name``
attribute to :class:`_declarative.ConcreteBase` so that the
virtual discriminator column name can be customized.
.. versionchanged:: 1.4.2 The ``_concrete_discriminator_name`` attribute
need only be placed on the basemost class to take correct effect for
all subclasses. An explicit error message is now raised if the
mapped column names conflict with the discriminator name, whereas
in the 1.3.x series there would be some warnings and then a non-useful
query would be generated.
.. seealso::
:class:`.AbstractConcreteBase`
:ref:`concrete_inheritance`
"""
@classmethod
def _create_polymorphic_union(cls, mappers, discriminator_name):
return polymorphic_union(
OrderedDict(
(mp.polymorphic_identity, mp.local_table) for mp in mappers
),
discriminator_name,
"pjoin",
)
@classmethod
def __declare_first__(cls):
m = cls.__mapper__
if m.with_polymorphic:
return
discriminator_name = (
getattr(cls, "_concrete_discriminator_name", None) or "type"
)
mappers = list(m.self_and_descendants)
pjoin = cls._create_polymorphic_union(mappers, discriminator_name)
m._set_with_polymorphic(("*", pjoin))
m._set_polymorphic_on(pjoin.c[discriminator_name])
class AbstractConcreteBase(ConcreteBase):
"""A helper class for 'concrete' declarative mappings.
:class:`.AbstractConcreteBase` will use the :func:`.polymorphic_union`
function automatically, against all tables mapped as a subclass
to this class. The function is called via the
``__declare_first__()`` function, which is essentially
a hook for the :meth:`.before_configured` event.
:class:`.AbstractConcreteBase` applies :class:`_orm.Mapper` for its
immediately inheriting class, as would occur for any other
declarative mapped class. However, the :class:`_orm.Mapper` is not
mapped to any particular :class:`.Table` object. Instead, it's
mapped directly to the "polymorphic" selectable produced by
:func:`.polymorphic_union`, and performs no persistence operations on its
own. Compare to :class:`.ConcreteBase`, which maps its
immediately inheriting class to an actual
:class:`.Table` that stores rows directly.
.. note::
The :class:`.AbstractConcreteBase` delays the mapper creation of the
base class until all the subclasses have been defined,
as it needs to create a mapping against a selectable that will include
all subclass tables. In order to achieve this, it waits for the
**mapper configuration event** to occur, at which point it scans
through all the configured subclasses and sets up a mapping that will
query against all subclasses at once.
While this event is normally invoked automatically, in the case of
:class:`.AbstractConcreteBase`, it may be necessary to invoke it
explicitly after **all** subclass mappings are defined, if the first
operation is to be a query against this base class. To do so, once all
the desired classes have been configured, the
:meth:`_orm.registry.configure` method on the :class:`_orm.registry`
in use can be invoked, which is available in relation to a particular
declarative base class::
Base.registry.configure()
Example::
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.ext.declarative import AbstractConcreteBase
class Base(DeclarativeBase):
pass
class Employee(AbstractConcreteBase, Base):
pass
class Manager(Employee):
__tablename__ = 'manager'
employee_id = Column(Integer, primary_key=True)
name = Column(String(50))
manager_data = Column(String(40))
__mapper_args__ = {
'polymorphic_identity':'manager',
'concrete':True
}
Base.registry.configure()
The abstract base class is handled by declarative in a special way;
at class configuration time, it behaves like a declarative mixin
or an ``__abstract__`` base class. Once classes are configured
and mappings are produced, it then gets mapped itself, but
after all of its descendants. This is a very unique system of mapping
not found in any other SQLAlchemy API feature.
Using this approach, we can specify columns and properties
that will take place on mapped subclasses, in the way that
we normally do as in :ref:`declarative_mixins`::
from sqlalchemy.ext.declarative import AbstractConcreteBase
class Company(Base):
__tablename__ = 'company'
id = Column(Integer, primary_key=True)
class Employee(AbstractConcreteBase, Base):
strict_attrs = True
employee_id = Column(Integer, primary_key=True)
@declared_attr
def company_id(cls):
return Column(ForeignKey('company.id'))
@declared_attr
def company(cls):
return relationship("Company")
class Manager(Employee):
__tablename__ = 'manager'
name = Column(String(50))
manager_data = Column(String(40))
__mapper_args__ = {
'polymorphic_identity':'manager',
'concrete':True
}
Base.registry.configure()
When we make use of our mappings however, both ``Manager`` and
``Employee`` will have an independently usable ``.company`` attribute::
session.execute(
select(Employee).filter(Employee.company.has(id=5))
)
:param strict_attrs: when specified on the base class, "strict" attribute
mode is enabled which attempts to limit ORM mapped attributes on the
base class to only those that are immediately present, while still
preserving "polymorphic" loading behavior.
.. versionadded:: 2.0
.. seealso::
:class:`.ConcreteBase`
:ref:`concrete_inheritance`
:ref:`abstract_concrete_base`
"""
__no_table__ = True
@classmethod
def __declare_first__(cls):
cls._sa_decl_prepare_nocascade()
@classmethod
def _sa_decl_prepare_nocascade(cls):
if getattr(cls, "__mapper__", None):
return
to_map = _DeferredMapperConfig.config_for_cls(cls)
# can't rely on 'self_and_descendants' here
# since technically an immediate subclass
# might not be mapped, but a subclass
# may be.
mappers = []
stack = list(cls.__subclasses__())
while stack:
klass = stack.pop()
stack.extend(klass.__subclasses__())
mn = _mapper_or_none(klass)
if mn is not None:
mappers.append(mn)
discriminator_name = (
getattr(cls, "_concrete_discriminator_name", None) or "type"
)
pjoin = cls._create_polymorphic_union(mappers, discriminator_name)
# For columns that were declared on the class, these
# are normally ignored with the "__no_table__" mapping,
# unless they have a different attribute key vs. col name
# and are in the properties argument.
# In that case, ensure we update the properties entry
# to the correct column from the pjoin target table.
declared_cols = set(to_map.declared_columns)
declared_col_keys = {c.key for c in declared_cols}
for k, v in list(to_map.properties.items()):
if v in declared_cols:
to_map.properties[k] = pjoin.c[v.key]
declared_col_keys.remove(v.key)
to_map.local_table = pjoin
strict_attrs = cls.__dict__.get("strict_attrs", False)
m_args = to_map.mapper_args_fn or dict
def mapper_args():
args = m_args()
args["polymorphic_on"] = pjoin.c[discriminator_name]
args["polymorphic_abstract"] = True
if strict_attrs:
args["include_properties"] = (
set(pjoin.primary_key)
| declared_col_keys
| {discriminator_name}
)
args["with_polymorphic"] = ("*", pjoin)
return args
to_map.mapper_args_fn = mapper_args
to_map.map()
stack = [cls]
while stack:
scls = stack.pop(0)
stack.extend(scls.__subclasses__())
sm = _mapper_or_none(scls)
if sm and sm.concrete and sm.inherits is None:
for sup_ in scls.__mro__[1:]:
sup_sm = _mapper_or_none(sup_)
if sup_sm:
sm._set_concrete_base(sup_sm)
break
@classmethod
def _sa_raise_deferred_config(cls):
raise orm_exc.UnmappedClassError(
cls,
msg="Class %s is a subclass of AbstractConcreteBase and "
"has a mapping pending until all subclasses are defined. "
"Call the sqlalchemy.orm.configure_mappers() function after "
"all subclasses have been defined to "
"complete the mapping of this class."
% orm_exc._safe_cls_name(cls),
)
class DeferredReflection:
"""A helper class for construction of mappings based on
a deferred reflection step.
Normally, declarative can be used with reflection by
setting a :class:`_schema.Table` object using autoload_with=engine
as the ``__table__`` attribute on a declarative class.
The caveat is that the :class:`_schema.Table` must be fully
reflected, or at the very least have a primary key column,
at the point at which a normal declarative mapping is
constructed, meaning the :class:`_engine.Engine` must be available
at class declaration time.
The :class:`.DeferredReflection` mixin moves the construction
of mappers to be at a later point, after a specific
method is called which first reflects all :class:`_schema.Table`
objects created so far. Classes can define it as such::
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import DeferredReflection
Base = declarative_base()
class MyClass(DeferredReflection, Base):
__tablename__ = 'mytable'
Above, ``MyClass`` is not yet mapped. After a series of
classes have been defined in the above fashion, all tables
can be reflected and mappings created using
:meth:`.prepare`::
engine = create_engine("someengine://...")
DeferredReflection.prepare(engine)
The :class:`.DeferredReflection` mixin can be applied to individual
classes, used as the base for the declarative base itself,
or used in a custom abstract class. Using an abstract base
allows that only a subset of classes to be prepared for a
particular prepare step, which is necessary for applications
that use more than one engine. For example, if an application
has two engines, you might use two bases, and prepare each
separately, e.g.::
class ReflectedOne(DeferredReflection, Base):
__abstract__ = True
class ReflectedTwo(DeferredReflection, Base):
__abstract__ = True
class MyClass(ReflectedOne):
__tablename__ = 'mytable'
class MyOtherClass(ReflectedOne):
__tablename__ = 'myothertable'
class YetAnotherClass(ReflectedTwo):
__tablename__ = 'yetanothertable'
# ... etc.
Above, the class hierarchies for ``ReflectedOne`` and
``ReflectedTwo`` can be configured separately::
ReflectedOne.prepare(engine_one)
ReflectedTwo.prepare(engine_two)
.. seealso::
:ref:`orm_declarative_reflected_deferred_reflection` - in the
:ref:`orm_declarative_table_config_toplevel` section.
"""
@classmethod
def prepare(
cls, bind: Union[Engine, Connection], **reflect_kw: Any
) -> None:
r"""Reflect all :class:`_schema.Table` objects for all current
:class:`.DeferredReflection` subclasses
:param bind: :class:`_engine.Engine` or :class:`_engine.Connection`
instance
..versionchanged:: 2.0.16 a :class:`_engine.Connection` is also
accepted.
:param \**reflect_kw: additional keyword arguments passed to
:meth:`_schema.MetaData.reflect`, such as
:paramref:`_schema.MetaData.reflect.views`.
.. versionadded:: 2.0.16
"""
to_map = _DeferredMapperConfig.classes_for_base(cls)
metadata_to_table = collections.defaultdict(set)
# first collect the primary __table__ for each class into a
# collection of metadata/schemaname -> table names
for thingy in to_map:
if thingy.local_table is not None:
metadata_to_table[
(thingy.local_table.metadata, thingy.local_table.schema)
].add(thingy.local_table.name)
# then reflect all those tables into their metadatas
if isinstance(bind, Connection):
conn = bind
ctx = contextlib.nullcontext(enter_result=conn)
elif isinstance(bind, Engine):
ctx = bind.connect()
else:
raise sa_exc.ArgumentError(
f"Expected Engine or Connection, got {bind!r}"
)
with ctx as conn:
for (metadata, schema), table_names in metadata_to_table.items():
metadata.reflect(
conn,
only=table_names,
schema=schema,
extend_existing=True,
autoload_replace=False,
**reflect_kw,
)
metadata_to_table.clear()
# .map() each class, then go through relationships and look
# for secondary
for thingy in to_map:
thingy.map()
mapper = thingy.cls.__mapper__
metadata = mapper.class_.metadata
for rel in mapper._props.values():
if (
isinstance(rel, relationships.RelationshipProperty)
and rel._init_args.secondary._is_populated()
):
secondary_arg = rel._init_args.secondary
if isinstance(secondary_arg.argument, Table):
secondary_table = secondary_arg.argument
metadata_to_table[
(
secondary_table.metadata,
secondary_table.schema,
)
].add(secondary_table.name)
elif isinstance(secondary_arg.argument, str):
_, resolve_arg = _resolver(rel.parent.class_, rel)
resolver = resolve_arg(
secondary_arg.argument, True
)
metadata_to_table[
(metadata, thingy.local_table.schema)
].add(secondary_arg.argument)
resolver._resolvers += (
cls._sa_deferred_table_resolver(metadata),
)
secondary_arg.argument = resolver()
for (metadata, schema), table_names in metadata_to_table.items():
metadata.reflect(
conn,
only=table_names,
schema=schema,
extend_existing=True,
autoload_replace=False,
)
@classmethod
def _sa_deferred_table_resolver(
cls, metadata: MetaData
) -> Callable[[str], Table]:
def _resolve(key: str) -> Table:
# reflection has already occurred so this Table would have
# its contents already
return Table(key, metadata)
return _resolve
_sa_decl_prepare = True
@classmethod
def _sa_raise_deferred_config(cls):
raise orm_exc.UnmappedClassError(
cls,
msg="Class %s is a subclass of DeferredReflection. "
"Mappings are not produced until the .prepare() "
"method is called on the class hierarchy."
% orm_exc._safe_cls_name(cls),
)