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# ext/hybrid.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
r"""Define attributes on ORM-mapped classes that have "hybrid" behavior.
"hybrid" means the attribute has distinct behaviors defined at the
class level and at the instance level.
The :mod:`~sqlalchemy.ext.hybrid` extension provides a special form of
method decorator and has minimal dependencies on the rest of SQLAlchemy.
Its basic theory of operation can work with any descriptor-based expression
system.
Consider a mapping ``Interval``, representing integer ``start`` and ``end``
values. We can define higher level functions on mapped classes that produce SQL
expressions at the class level, and Python expression evaluation at the
instance level. Below, each function decorated with :class:`.hybrid_method` or
:class:`.hybrid_property` may receive ``self`` as an instance of the class, or
may receive the class directly, depending on context::
from __future__ import annotations
from sqlalchemy.ext.hybrid import hybrid_method
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped
from sqlalchemy.orm import mapped_column
class Base(DeclarativeBase):
pass
class Interval(Base):
__tablename__ = 'interval'
id: Mapped[int] = mapped_column(primary_key=True)
start: Mapped[int]
end: Mapped[int]
def __init__(self, start: int, end: int):
self.start = start
self.end = end
@hybrid_property
def length(self) -> int:
return self.end - self.start
@hybrid_method
def contains(self, point: int) -> bool:
return (self.start <= point) & (point <= self.end)
@hybrid_method
def intersects(self, other: Interval) -> bool:
return self.contains(other.start) | self.contains(other.end)
Above, the ``length`` property returns the difference between the
``end`` and ``start`` attributes. With an instance of ``Interval``,
this subtraction occurs in Python, using normal Python descriptor
mechanics::
>>> i1 = Interval(5, 10)
>>> i1.length
5
When dealing with the ``Interval`` class itself, the :class:`.hybrid_property`
descriptor evaluates the function body given the ``Interval`` class as
the argument, which when evaluated with SQLAlchemy expression mechanics
returns a new SQL expression:
.. sourcecode:: pycon+sql
>>> from sqlalchemy import select
>>> print(select(Interval.length))
{printsql}SELECT interval."end" - interval.start AS length
FROM interval{stop}
>>> print(select(Interval).filter(Interval.length > 10))
{printsql}SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval."end" - interval.start > :param_1
Filtering methods such as :meth:`.Select.filter_by` are supported
with hybrid attributes as well:
.. sourcecode:: pycon+sql
>>> print(select(Interval).filter_by(length=5))
{printsql}SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval."end" - interval.start = :param_1
The ``Interval`` class example also illustrates two methods,
``contains()`` and ``intersects()``, decorated with
:class:`.hybrid_method`. This decorator applies the same idea to
methods that :class:`.hybrid_property` applies to attributes. The
methods return boolean values, and take advantage of the Python ``|``
and ``&`` bitwise operators to produce equivalent instance-level and
SQL expression-level boolean behavior:
.. sourcecode:: pycon+sql
>>> i1.contains(6)
True
>>> i1.contains(15)
False
>>> i1.intersects(Interval(7, 18))
True
>>> i1.intersects(Interval(25, 29))
False
>>> print(select(Interval).filter(Interval.contains(15)))
{printsql}SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval.start <= :start_1 AND interval."end" > :end_1{stop}
>>> ia = aliased(Interval)
>>> print(select(Interval, ia).filter(Interval.intersects(ia)))
{printsql}SELECT interval.id, interval.start,
interval."end", interval_1.id AS interval_1_id,
interval_1.start AS interval_1_start, interval_1."end" AS interval_1_end
FROM interval, interval AS interval_1
WHERE interval.start <= interval_1.start
AND interval."end" > interval_1.start
OR interval.start <= interval_1."end"
AND interval."end" > interval_1."end"{stop}
.. _hybrid_distinct_expression:
Defining Expression Behavior Distinct from Attribute Behavior
--------------------------------------------------------------
In the previous section, our usage of the ``&`` and ``|`` bitwise operators
within the ``Interval.contains`` and ``Interval.intersects`` methods was
fortunate, considering our functions operated on two boolean values to return a
new one. In many cases, the construction of an in-Python function and a
SQLAlchemy SQL expression have enough differences that two separate Python
expressions should be defined. The :mod:`~sqlalchemy.ext.hybrid` decorator
defines a **modifier** :meth:`.hybrid_property.expression` for this purpose. As an
example we'll define the radius of the interval, which requires the usage of
the absolute value function::
from sqlalchemy import ColumnElement
from sqlalchemy import Float
from sqlalchemy import func
from sqlalchemy import type_coerce
class Interval(Base):
# ...
@hybrid_property
def radius(self) -> float:
return abs(self.length) / 2
@radius.inplace.expression
@classmethod
def _radius_expression(cls) -> ColumnElement[float]:
return type_coerce(func.abs(cls.length) / 2, Float)
In the above example, the :class:`.hybrid_property` first assigned to the
name ``Interval.radius`` is amended by a subsequent method called
``Interval._radius_expression``, using the decorator
``@radius.inplace.expression``, which chains together two modifiers
:attr:`.hybrid_property.inplace` and :attr:`.hybrid_property.expression`.
The use of :attr:`.hybrid_property.inplace` indicates that the
:meth:`.hybrid_property.expression` modifier should mutate the
existing hybrid object at ``Interval.radius`` in place, without creating a
new object. Notes on this modifier and its
rationale are discussed in the next section :ref:`hybrid_pep484_naming`.
The use of ``@classmethod`` is optional, and is strictly to give typing
tools a hint that ``cls`` in this case is expected to be the ``Interval``
class, and not an instance of ``Interval``.
.. note:: :attr:`.hybrid_property.inplace` as well as the use of ``@classmethod``
for proper typing support are available as of SQLAlchemy 2.0.4, and will
not work in earlier versions.
With ``Interval.radius`` now including an expression element, the SQL
function ``ABS()`` is returned when accessing ``Interval.radius``
at the class level:
.. sourcecode:: pycon+sql
>>> from sqlalchemy import select
>>> print(select(Interval).filter(Interval.radius > 5))
{printsql}SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE abs(interval."end" - interval.start) / :abs_1 > :param_1
.. _hybrid_pep484_naming:
Using ``inplace`` to create pep-484 compliant hybrid properties
---------------------------------------------------------------
In the previous section, a :class:`.hybrid_property` decorator is illustrated
which includes two separate method-level functions being decorated, both
to produce a single object attribute referenced as ``Interval.radius``.
There are actually several different modifiers we can use for
:class:`.hybrid_property` including :meth:`.hybrid_property.expression`,
:meth:`.hybrid_property.setter` and :meth:`.hybrid_property.update_expression`.
SQLAlchemy's :class:`.hybrid_property` decorator intends that adding on these
methods may be done in the identical manner as Python's built-in
``@property`` decorator, where idiomatic use is to continue to redefine the
attribute repeatedly, using the **same attribute name** each time, as in the
example below that illustrates the use of :meth:`.hybrid_property.setter` and
:meth:`.hybrid_property.expression` for the ``Interval.radius`` descriptor::
# correct use, however is not accepted by pep-484 tooling
class Interval(Base):
# ...
@hybrid_property
def radius(self):
return abs(self.length) / 2
@radius.setter
def radius(self, value):
self.length = value * 2
@radius.expression
def radius(cls):
return type_coerce(func.abs(cls.length) / 2, Float)
Above, there are three ``Interval.radius`` methods, but as each are decorated,
first by the :class:`.hybrid_property` decorator and then by the
``@radius`` name itself, the end effect is that ``Interval.radius`` is
a single attribute with three different functions contained within it.
This style of use is taken from `Python's documented use of @property
<https://docs.python.org/3/library/functions.html#property>`_.
It is important to note that the way both ``@property`` as well as
:class:`.hybrid_property` work, a **copy of the descriptor is made each time**.
That is, each call to ``@radius.expression``, ``@radius.setter`` etc.
make a new object entirely. This allows the attribute to be re-defined in
subclasses without issue (see :ref:`hybrid_reuse_subclass` later in this
section for how this is used).
However, the above approach is not compatible with typing tools such as
mypy and pyright. Python's own ``@property`` decorator does not have this
limitation only because
`these tools hardcode the behavior of @property
<https://github.com/python/typing/discussions/1102>`_, meaning this syntax
is not available to SQLAlchemy under :pep:`484` compliance.
In order to produce a reasonable syntax while remaining typing compliant,
the :attr:`.hybrid_property.inplace` decorator allows the same
decorator to be re-used with different method names, while still producing
a single decorator under one name::
# correct use which is also accepted by pep-484 tooling
class Interval(Base):
# ...
@hybrid_property
def radius(self) -> float:
return abs(self.length) / 2
@radius.inplace.setter
def _radius_setter(self, value: float) -> None:
# for example only
self.length = value * 2
@radius.inplace.expression
@classmethod
def _radius_expression(cls) -> ColumnElement[float]:
return type_coerce(func.abs(cls.length) / 2, Float)
Using :attr:`.hybrid_property.inplace` further qualifies the use of the
decorator that a new copy should not be made, thereby maintaining the
``Interval.radius`` name while allowing additional methods
``Interval._radius_setter`` and ``Interval._radius_expression`` to be
differently named.
.. versionadded:: 2.0.4 Added :attr:`.hybrid_property.inplace` to allow
less verbose construction of composite :class:`.hybrid_property` objects
while not having to use repeated method names. Additionally allowed the
use of ``@classmethod`` within :attr:`.hybrid_property.expression`,
:attr:`.hybrid_property.update_expression`, and
:attr:`.hybrid_property.comparator` to allow typing tools to identify
``cls`` as a class and not an instance in the method signature.
Defining Setters
----------------
The :meth:`.hybrid_property.setter` modifier allows the construction of a
custom setter method, that can modify values on the object::
class Interval(Base):
# ...
@hybrid_property
def length(self) -> int:
return self.end - self.start
@length.inplace.setter
def _length_setter(self, value: int) -> None:
self.end = self.start + value
The ``length(self, value)`` method is now called upon set::
>>> i1 = Interval(5, 10)
>>> i1.length
5
>>> i1.length = 12
>>> i1.end
17
.. _hybrid_bulk_update:
Allowing Bulk ORM Update
------------------------
A hybrid can define a custom "UPDATE" handler for when using
ORM-enabled updates, allowing the hybrid to be used in the
SET clause of the update.
Normally, when using a hybrid with :func:`_sql.update`, the SQL
expression is used as the column that's the target of the SET. If our
``Interval`` class had a hybrid ``start_point`` that linked to
``Interval.start``, this could be substituted directly::
from sqlalchemy import update
stmt = update(Interval).values({Interval.start_point: 10})
However, when using a composite hybrid like ``Interval.length``, this
hybrid represents more than one column. We can set up a handler that will
accommodate a value passed in the VALUES expression which can affect
this, using the :meth:`.hybrid_property.update_expression` decorator.
A handler that works similarly to our setter would be::
from typing import List, Tuple, Any
class Interval(Base):
# ...
@hybrid_property
def length(self) -> int:
return self.end - self.start
@length.inplace.setter
def _length_setter(self, value: int) -> None:
self.end = self.start + value
@length.inplace.update_expression
def _length_update_expression(cls, value: Any) -> List[Tuple[Any, Any]]:
return [
(cls.end, cls.start + value)
]
Above, if we use ``Interval.length`` in an UPDATE expression, we get
a hybrid SET expression:
.. sourcecode:: pycon+sql
>>> from sqlalchemy import update
>>> print(update(Interval).values({Interval.length: 25}))
{printsql}UPDATE interval SET "end"=(interval.start + :start_1)
This SET expression is accommodated by the ORM automatically.
.. seealso::
:ref:`orm_expression_update_delete` - includes background on ORM-enabled
UPDATE statements
Working with Relationships
--------------------------
There's no essential difference when creating hybrids that work with
related objects as opposed to column-based data. The need for distinct
expressions tends to be greater. The two variants we'll illustrate
are the "join-dependent" hybrid, and the "correlated subquery" hybrid.
Join-Dependent Relationship Hybrid
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Consider the following declarative
mapping which relates a ``User`` to a ``SavingsAccount``::
from __future__ import annotations
from decimal import Decimal
from typing import cast
from typing import List
from typing import Optional
from sqlalchemy import ForeignKey
from sqlalchemy import Numeric
from sqlalchemy import String
from sqlalchemy import SQLColumnExpression
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped
from sqlalchemy.orm import mapped_column
from sqlalchemy.orm import relationship
class Base(DeclarativeBase):
pass
class SavingsAccount(Base):
__tablename__ = 'account'
id: Mapped[int] = mapped_column(primary_key=True)
user_id: Mapped[int] = mapped_column(ForeignKey('user.id'))
balance: Mapped[Decimal] = mapped_column(Numeric(15, 5))
owner: Mapped[User] = relationship(back_populates="accounts")
class User(Base):
__tablename__ = 'user'
id: Mapped[int] = mapped_column(primary_key=True)
name: Mapped[str] = mapped_column(String(100))
accounts: Mapped[List[SavingsAccount]] = relationship(
back_populates="owner", lazy="selectin"
)
@hybrid_property
def balance(self) -> Optional[Decimal]:
if self.accounts:
return self.accounts[0].balance
else:
return None
@balance.inplace.setter
def _balance_setter(self, value: Optional[Decimal]) -> None:
assert value is not None
if not self.accounts:
account = SavingsAccount(owner=self)
else:
account = self.accounts[0]
account.balance = value
@balance.inplace.expression
@classmethod
def _balance_expression(cls) -> SQLColumnExpression[Optional[Decimal]]:
return cast("SQLColumnExpression[Optional[Decimal]]", SavingsAccount.balance)
The above hybrid property ``balance`` works with the first
``SavingsAccount`` entry in the list of accounts for this user. The
in-Python getter/setter methods can treat ``accounts`` as a Python
list available on ``self``.
.. tip:: The ``User.balance`` getter in the above example accesses the
``self.acccounts`` collection, which will normally be loaded via the
:func:`.selectinload` loader strategy configured on the ``User.balance``
:func:`_orm.relationship`. The default loader strategy when not otherwise
stated on :func:`_orm.relationship` is :func:`.lazyload`, which emits SQL on
demand. When using asyncio, on-demand loaders such as :func:`.lazyload` are
not supported, so care should be taken to ensure the ``self.accounts``
collection is accessible to this hybrid accessor when using asyncio.
At the expression level, it's expected that the ``User`` class will
be used in an appropriate context such that an appropriate join to
``SavingsAccount`` will be present:
.. sourcecode:: pycon+sql
>>> from sqlalchemy import select
>>> print(select(User, User.balance).
... join(User.accounts).filter(User.balance > 5000))
{printsql}SELECT "user".id AS user_id, "user".name AS user_name,
account.balance AS account_balance
FROM "user" JOIN account ON "user".id = account.user_id
WHERE account.balance > :balance_1
Note however, that while the instance level accessors need to worry
about whether ``self.accounts`` is even present, this issue expresses
itself differently at the SQL expression level, where we basically
would use an outer join:
.. sourcecode:: pycon+sql
>>> from sqlalchemy import select
>>> from sqlalchemy import or_
>>> print (select(User, User.balance).outerjoin(User.accounts).
... filter(or_(User.balance < 5000, User.balance == None)))
{printsql}SELECT "user".id AS user_id, "user".name AS user_name,
account.balance AS account_balance
FROM "user" LEFT OUTER JOIN account ON "user".id = account.user_id
WHERE account.balance < :balance_1 OR account.balance IS NULL
Correlated Subquery Relationship Hybrid
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
We can, of course, forego being dependent on the enclosing query's usage
of joins in favor of the correlated subquery, which can portably be packed
into a single column expression. A correlated subquery is more portable, but
often performs more poorly at the SQL level. Using the same technique
illustrated at :ref:`mapper_column_property_sql_expressions`,
we can adjust our ``SavingsAccount`` example to aggregate the balances for
*all* accounts, and use a correlated subquery for the column expression::
from __future__ import annotations
from decimal import Decimal
from typing import List
from sqlalchemy import ForeignKey
from sqlalchemy import func
from sqlalchemy import Numeric
from sqlalchemy import select
from sqlalchemy import SQLColumnExpression
from sqlalchemy import String
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped
from sqlalchemy.orm import mapped_column
from sqlalchemy.orm import relationship
class Base(DeclarativeBase):
pass
class SavingsAccount(Base):
__tablename__ = 'account'
id: Mapped[int] = mapped_column(primary_key=True)
user_id: Mapped[int] = mapped_column(ForeignKey('user.id'))
balance: Mapped[Decimal] = mapped_column(Numeric(15, 5))
owner: Mapped[User] = relationship(back_populates="accounts")
class User(Base):
__tablename__ = 'user'
id: Mapped[int] = mapped_column(primary_key=True)
name: Mapped[str] = mapped_column(String(100))
accounts: Mapped[List[SavingsAccount]] = relationship(
back_populates="owner", lazy="selectin"
)
@hybrid_property
def balance(self) -> Decimal:
return sum((acc.balance for acc in self.accounts), start=Decimal("0"))
@balance.inplace.expression
@classmethod
def _balance_expression(cls) -> SQLColumnExpression[Decimal]:
return (
select(func.sum(SavingsAccount.balance))
.where(SavingsAccount.user_id == cls.id)
.label("total_balance")
)
The above recipe will give us the ``balance`` column which renders
a correlated SELECT:
.. sourcecode:: pycon+sql
>>> from sqlalchemy import select
>>> print(select(User).filter(User.balance > 400))
{printsql}SELECT "user".id, "user".name
FROM "user"
WHERE (
SELECT sum(account.balance) AS sum_1 FROM account
WHERE account.user_id = "user".id
) > :param_1
.. _hybrid_custom_comparators:
Building Custom Comparators
---------------------------
The hybrid property also includes a helper that allows construction of
custom comparators. A comparator object allows one to customize the
behavior of each SQLAlchemy expression operator individually. They
are useful when creating custom types that have some highly
idiosyncratic behavior on the SQL side.
.. note:: The :meth:`.hybrid_property.comparator` decorator introduced
in this section **replaces** the use of the
:meth:`.hybrid_property.expression` decorator.
They cannot be used together.
The example class below allows case-insensitive comparisons on the attribute
named ``word_insensitive``::
from __future__ import annotations
from typing import Any
from sqlalchemy import ColumnElement
from sqlalchemy import func
from sqlalchemy.ext.hybrid import Comparator
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.orm import Mapped
from sqlalchemy.orm import mapped_column
class Base(DeclarativeBase):
pass
class CaseInsensitiveComparator(Comparator[str]):
def __eq__(self, other: Any) -> ColumnElement[bool]: # type: ignore[override] # noqa: E501
return func.lower(self.__clause_element__()) == func.lower(other)
class SearchWord(Base):
__tablename__ = 'searchword'
id: Mapped[int] = mapped_column(primary_key=True)
word: Mapped[str]
@hybrid_property
def word_insensitive(self) -> str:
return self.word.lower()
@word_insensitive.inplace.comparator
@classmethod
def _word_insensitive_comparator(cls) -> CaseInsensitiveComparator:
return CaseInsensitiveComparator(cls.word)
Above, SQL expressions against ``word_insensitive`` will apply the ``LOWER()``
SQL function to both sides:
.. sourcecode:: pycon+sql
>>> from sqlalchemy import select
>>> print(select(SearchWord).filter_by(word_insensitive="Trucks"))
{printsql}SELECT searchword.id, searchword.word
FROM searchword
WHERE lower(searchword.word) = lower(:lower_1)
The ``CaseInsensitiveComparator`` above implements part of the
:class:`.ColumnOperators` interface. A "coercion" operation like
lowercasing can be applied to all comparison operations (i.e. ``eq``,
``lt``, ``gt``, etc.) using :meth:`.Operators.operate`::
class CaseInsensitiveComparator(Comparator):
def operate(self, op, other, **kwargs):
return op(
func.lower(self.__clause_element__()),
func.lower(other),
**kwargs,
)
.. _hybrid_reuse_subclass:
Reusing Hybrid Properties across Subclasses
-------------------------------------------
A hybrid can be referred to from a superclass, to allow modifying
methods like :meth:`.hybrid_property.getter`, :meth:`.hybrid_property.setter`
to be used to redefine those methods on a subclass. This is similar to
how the standard Python ``@property`` object works::
class FirstNameOnly(Base):
# ...
first_name: Mapped[str]
@hybrid_property
def name(self) -> str:
return self.first_name
@name.inplace.setter
def _name_setter(self, value: str) -> None:
self.first_name = value
class FirstNameLastName(FirstNameOnly):
# ...
last_name: Mapped[str]
# 'inplace' is not used here; calling getter creates a copy
# of FirstNameOnly.name that is local to FirstNameLastName
@FirstNameOnly.name.getter
def name(self) -> str:
return self.first_name + ' ' + self.last_name
@name.inplace.setter
def _name_setter(self, value: str) -> None:
self.first_name, self.last_name = value.split(' ', 1)
Above, the ``FirstNameLastName`` class refers to the hybrid from
``FirstNameOnly.name`` to repurpose its getter and setter for the subclass.
When overriding :meth:`.hybrid_property.expression` and
:meth:`.hybrid_property.comparator` alone as the first reference to the
superclass, these names conflict with the same-named accessors on the class-
level :class:`.QueryableAttribute` object returned at the class level. To
override these methods when referring directly to the parent class descriptor,
add the special qualifier :attr:`.hybrid_property.overrides`, which will de-
reference the instrumented attribute back to the hybrid object::
class FirstNameLastName(FirstNameOnly):
# ...
last_name: Mapped[str]
@FirstNameOnly.name.overrides.expression
@classmethod
def name(cls):
return func.concat(cls.first_name, ' ', cls.last_name)
Hybrid Value Objects
--------------------
Note in our previous example, if we were to compare the ``word_insensitive``
attribute of a ``SearchWord`` instance to a plain Python string, the plain
Python string would not be coerced to lower case - the
``CaseInsensitiveComparator`` we built, being returned by
``@word_insensitive.comparator``, only applies to the SQL side.
A more comprehensive form of the custom comparator is to construct a *Hybrid
Value Object*. This technique applies the target value or expression to a value
object which is then returned by the accessor in all cases. The value object
allows control of all operations upon the value as well as how compared values
are treated, both on the SQL expression side as well as the Python value side.
Replacing the previous ``CaseInsensitiveComparator`` class with a new
``CaseInsensitiveWord`` class::
class CaseInsensitiveWord(Comparator):
"Hybrid value representing a lower case representation of a word."
def __init__(self, word):
if isinstance(word, basestring):
self.word = word.lower()
elif isinstance(word, CaseInsensitiveWord):
self.word = word.word
else:
self.word = func.lower(word)
def operate(self, op, other, **kwargs):
if not isinstance(other, CaseInsensitiveWord):
other = CaseInsensitiveWord(other)
return op(self.word, other.word, **kwargs)
def __clause_element__(self):
return self.word
def __str__(self):
return self.word
key = 'word'
"Label to apply to Query tuple results"
Above, the ``CaseInsensitiveWord`` object represents ``self.word``, which may
be a SQL function, or may be a Python native. By overriding ``operate()`` and
``__clause_element__()`` to work in terms of ``self.word``, all comparison
operations will work against the "converted" form of ``word``, whether it be
SQL side or Python side. Our ``SearchWord`` class can now deliver the
``CaseInsensitiveWord`` object unconditionally from a single hybrid call::
class SearchWord(Base):
__tablename__ = 'searchword'
id: Mapped[int] = mapped_column(primary_key=True)
word: Mapped[str]
@hybrid_property
def word_insensitive(self) -> CaseInsensitiveWord:
return CaseInsensitiveWord(self.word)
The ``word_insensitive`` attribute now has case-insensitive comparison behavior
universally, including SQL expression vs. Python expression (note the Python
value is converted to lower case on the Python side here):
.. sourcecode:: pycon+sql
>>> print(select(SearchWord).filter_by(word_insensitive="Trucks"))
{printsql}SELECT searchword.id AS searchword_id, searchword.word AS searchword_word
FROM searchword
WHERE lower(searchword.word) = :lower_1
SQL expression versus SQL expression:
.. sourcecode:: pycon+sql
>>> from sqlalchemy.orm import aliased
>>> sw1 = aliased(SearchWord)
>>> sw2 = aliased(SearchWord)
>>> print(
... select(sw1.word_insensitive, sw2.word_insensitive).filter(
... sw1.word_insensitive > sw2.word_insensitive
... )
... )
{printsql}SELECT lower(searchword_1.word) AS lower_1,
lower(searchword_2.word) AS lower_2
FROM searchword AS searchword_1, searchword AS searchword_2
WHERE lower(searchword_1.word) > lower(searchword_2.word)
Python only expression::
>>> ws1 = SearchWord(word="SomeWord")
>>> ws1.word_insensitive == "sOmEwOrD"
True
>>> ws1.word_insensitive == "XOmEwOrX"
False
>>> print(ws1.word_insensitive)
someword
The Hybrid Value pattern is very useful for any kind of value that may have
multiple representations, such as timestamps, time deltas, units of
measurement, currencies and encrypted passwords.
.. seealso::
`Hybrids and Value Agnostic Types
<https://techspot.zzzeek.org/2011/10/21/hybrids-and-value-agnostic-types/>`_
- on the techspot.zzzeek.org blog
`Value Agnostic Types, Part II
<https://techspot.zzzeek.org/2011/10/29/value-agnostic-types-part-ii/>`_ -
on the techspot.zzzeek.org blog
""" # noqa
from __future__ import annotations
from typing import Any
from typing import Callable
from typing import cast
from typing import Generic
from typing import List
from typing import Optional
from typing import overload
from typing import Sequence
from typing import Tuple
from typing import Type
from typing import TYPE_CHECKING
from typing import TypeVar
from typing import Union
from .. import util
from ..orm import attributes
from ..orm import InspectionAttrExtensionType
from ..orm import interfaces
from ..orm import ORMDescriptor
from ..orm.attributes import QueryableAttribute
from ..sql import roles
from ..sql._typing import is_has_clause_element
from ..sql.elements import ColumnElement
from ..sql.elements import SQLCoreOperations
from ..util.typing import Concatenate
from ..util.typing import Literal
from ..util.typing import ParamSpec
from ..util.typing import Protocol
from ..util.typing import Self
if TYPE_CHECKING:
from ..orm.interfaces import MapperProperty
from ..orm.util import AliasedInsp
from ..sql import SQLColumnExpression
from ..sql._typing import _ColumnExpressionArgument
from ..sql._typing import _DMLColumnArgument
from ..sql._typing import _HasClauseElement
from ..sql._typing import _InfoType
from ..sql.operators import OperatorType
_P = ParamSpec("_P")
_R = TypeVar("_R")
_T = TypeVar("_T", bound=Any)
_TE = TypeVar("_TE", bound=Any)
_T_co = TypeVar("_T_co", bound=Any, covariant=True)
_T_con = TypeVar("_T_con", bound=Any, contravariant=True)
class HybridExtensionType(InspectionAttrExtensionType):
HYBRID_METHOD = "HYBRID_METHOD"
"""Symbol indicating an :class:`InspectionAttr` that's
of type :class:`.hybrid_method`.
Is assigned to the :attr:`.InspectionAttr.extension_type`
attribute.
.. seealso::
:attr:`_orm.Mapper.all_orm_attributes`
"""
HYBRID_PROPERTY = "HYBRID_PROPERTY"
"""Symbol indicating an :class:`InspectionAttr` that's
of type :class:`.hybrid_method`.
Is assigned to the :attr:`.InspectionAttr.extension_type`
attribute.
.. seealso::
:attr:`_orm.Mapper.all_orm_attributes`
"""
class _HybridGetterType(Protocol[_T_co]):
def __call__(s, self: Any) -> _T_co: ...
class _HybridSetterType(Protocol[_T_con]):
def __call__(s, self: Any, value: _T_con) -> None: ...
class _HybridUpdaterType(Protocol[_T_con]):
def __call__(
s,
cls: Any,
value: Union[_T_con, _ColumnExpressionArgument[_T_con]],
) -> List[Tuple[_DMLColumnArgument, Any]]: ...
class _HybridDeleterType(Protocol[_T_co]):
def __call__(s, self: Any) -> None: ...
class _HybridExprCallableType(Protocol[_T_co]):
def __call__(
s, cls: Any
) -> Union[_HasClauseElement[_T_co], SQLColumnExpression[_T_co]]: ...
class _HybridComparatorCallableType(Protocol[_T]):
def __call__(self, cls: Any) -> Comparator[_T]: ...
class _HybridClassLevelAccessor(QueryableAttribute[_T]):
"""Describe the object returned by a hybrid_property() when
called as a class-level descriptor.
"""
if TYPE_CHECKING:
def getter(
self, fget: _HybridGetterType[_T]
) -> hybrid_property[_T]: ...
def setter(
self, fset: _HybridSetterType[_T]
) -> hybrid_property[_T]: ...
def deleter(
self, fdel: _HybridDeleterType[_T]
) -> hybrid_property[_T]: ...
@property
def overrides(self) -> hybrid_property[_T]: ...
def update_expression(
self, meth: _HybridUpdaterType[_T]
) -> hybrid_property[_T]: ...
class hybrid_method(interfaces.InspectionAttrInfo, Generic[_P, _R]):
"""A decorator which allows definition of a Python object method with both
instance-level and class-level behavior.
"""
is_attribute = True
extension_type = HybridExtensionType.HYBRID_METHOD
def __init__(
self,
func: Callable[Concatenate[Any, _P], _R],
expr: Optional[
Callable[Concatenate[Any, _P], SQLCoreOperations[_R]]
] = None,
):
"""Create a new :class:`.hybrid_method`.
Usage is typically via decorator::
from sqlalchemy.ext.hybrid import hybrid_method
class SomeClass:
@hybrid_method
def value(self, x, y):
return self._value + x + y
@value.expression
@classmethod
def value(cls, x, y):
return func.some_function(cls._value, x, y)
"""
self.func = func
if expr is not None:
self.expression(expr)
else:
self.expression(func) # type: ignore
@property
def inplace(self) -> Self:
"""Return the inplace mutator for this :class:`.hybrid_method`.
The :class:`.hybrid_method` class already performs "in place" mutation
when the :meth:`.hybrid_method.expression` decorator is called,
so this attribute returns Self.
.. versionadded:: 2.0.4
.. seealso::
:ref:`hybrid_pep484_naming`
"""
return self
@overload
def __get__(
self, instance: Literal[None], owner: Type[object]
) -> Callable[_P, SQLCoreOperations[_R]]: ...
@overload
def __get__(
self, instance: object, owner: Type[object]
) -> Callable[_P, _R]: ...
def __get__(
self, instance: Optional[object], owner: Type[object]
) -> Union[Callable[_P, _R], Callable[_P, SQLCoreOperations[_R]]]:
if instance is None:
return self.expr.__get__(owner, owner) # type: ignore
else:
return self.func.__get__(instance, owner) # type: ignore
def expression(
self, expr: Callable[Concatenate[Any, _P], SQLCoreOperations[_R]]
) -> hybrid_method[_P, _R]:
"""Provide a modifying decorator that defines a
SQL-expression producing method."""
self.expr = expr
if not self.expr.__doc__:
self.expr.__doc__ = self.func.__doc__
return self
def _unwrap_classmethod(meth: _T) -> _T:
if isinstance(meth, classmethod):
return meth.__func__ # type: ignore
else:
return meth
class hybrid_property(interfaces.InspectionAttrInfo, ORMDescriptor[_T]):
"""A decorator which allows definition of a Python descriptor with both
instance-level and class-level behavior.
"""
is_attribute = True
extension_type = HybridExtensionType.HYBRID_PROPERTY
__name__: str
def __init__(
self,
fget: _HybridGetterType[_T],
fset: Optional[_HybridSetterType[_T]] = None,
fdel: Optional[_HybridDeleterType[_T]] = None,
expr: Optional[_HybridExprCallableType[_T]] = None,
custom_comparator: Optional[Comparator[_T]] = None,
update_expr: Optional[_HybridUpdaterType[_T]] = None,
):
"""Create a new :class:`.hybrid_property`.
Usage is typically via decorator::
from sqlalchemy.ext.hybrid import hybrid_property
class SomeClass:
@hybrid_property
def value(self):
return self._value
@value.setter
def value(self, value):
self._value = value
"""
self.fget = fget
self.fset = fset
self.fdel = fdel
self.expr = _unwrap_classmethod(expr)
self.custom_comparator = _unwrap_classmethod(custom_comparator)
self.update_expr = _unwrap_classmethod(update_expr)
util.update_wrapper(self, fget) # type: ignore[arg-type]
@overload
def __get__(self, instance: Any, owner: Literal[None]) -> Self: ...
@overload
def __get__(
self, instance: Literal[None], owner: Type[object]
) -> _HybridClassLevelAccessor[_T]: ...
@overload
def __get__(self, instance: object, owner: Type[object]) -> _T: ...
def __get__(
self, instance: Optional[object], owner: Optional[Type[object]]
) -> Union[hybrid_property[_T], _HybridClassLevelAccessor[_T], _T]:
if owner is None:
return self
elif instance is None:
return self._expr_comparator(owner)
else:
return self.fget(instance)
def __set__(self, instance: object, value: Any) -> None:
if self.fset is None:
raise AttributeError("can't set attribute")
self.fset(instance, value)
def __delete__(self, instance: object) -> None:
if self.fdel is None:
raise AttributeError("can't delete attribute")
self.fdel(instance)
def _copy(self, **kw: Any) -> hybrid_property[_T]:
defaults = {
key: value
for key, value in self.__dict__.items()
if not key.startswith("_")
}
defaults.update(**kw)
return type(self)(**defaults)
@property
def overrides(self) -> Self:
"""Prefix for a method that is overriding an existing attribute.
The :attr:`.hybrid_property.overrides` accessor just returns
this hybrid object, which when called at the class level from
a parent class, will de-reference the "instrumented attribute"
normally returned at this level, and allow modifying decorators
like :meth:`.hybrid_property.expression` and
:meth:`.hybrid_property.comparator`
to be used without conflicting with the same-named attributes
normally present on the :class:`.QueryableAttribute`::
class SuperClass:
# ...
@hybrid_property
def foobar(self):
return self._foobar
class SubClass(SuperClass):
# ...
@SuperClass.foobar.overrides.expression
def foobar(cls):
return func.subfoobar(self._foobar)
.. versionadded:: 1.2
.. seealso::
:ref:`hybrid_reuse_subclass`
"""
return self
class _InPlace(Generic[_TE]):
"""A builder helper for .hybrid_property.
.. versionadded:: 2.0.4
"""
__slots__ = ("attr",)
def __init__(self, attr: hybrid_property[_TE]):
self.attr = attr
def _set(self, **kw: Any) -> hybrid_property[_TE]:
for k, v in kw.items():
setattr(self.attr, k, _unwrap_classmethod(v))
return self.attr
def getter(self, fget: _HybridGetterType[_TE]) -> hybrid_property[_TE]:
return self._set(fget=fget)
def setter(self, fset: _HybridSetterType[_TE]) -> hybrid_property[_TE]:
return self._set(fset=fset)
def deleter(
self, fdel: _HybridDeleterType[_TE]
) -> hybrid_property[_TE]:
return self._set(fdel=fdel)
def expression(
self, expr: _HybridExprCallableType[_TE]
) -> hybrid_property[_TE]:
return self._set(expr=expr)
def comparator(
self, comparator: _HybridComparatorCallableType[_TE]
) -> hybrid_property[_TE]:
return self._set(custom_comparator=comparator)
def update_expression(
self, meth: _HybridUpdaterType[_TE]
) -> hybrid_property[_TE]:
return self._set(update_expr=meth)
@property
def inplace(self) -> _InPlace[_T]:
"""Return the inplace mutator for this :class:`.hybrid_property`.
This is to allow in-place mutation of the hybrid, allowing the first
hybrid method of a certain name to be re-used in order to add
more methods without having to name those methods the same, e.g.::
class Interval(Base):
# ...
@hybrid_property
def radius(self) -> float:
return abs(self.length) / 2
@radius.inplace.setter
def _radius_setter(self, value: float) -> None:
self.length = value * 2
@radius.inplace.expression
def _radius_expression(cls) -> ColumnElement[float]:
return type_coerce(func.abs(cls.length) / 2, Float)
.. versionadded:: 2.0.4
.. seealso::
:ref:`hybrid_pep484_naming`
"""
return hybrid_property._InPlace(self)
def getter(self, fget: _HybridGetterType[_T]) -> hybrid_property[_T]:
"""Provide a modifying decorator that defines a getter method.
.. versionadded:: 1.2
"""
return self._copy(fget=fget)
def setter(self, fset: _HybridSetterType[_T]) -> hybrid_property[_T]:
"""Provide a modifying decorator that defines a setter method."""
return self._copy(fset=fset)
def deleter(self, fdel: _HybridDeleterType[_T]) -> hybrid_property[_T]:
"""Provide a modifying decorator that defines a deletion method."""
return self._copy(fdel=fdel)
def expression(
self, expr: _HybridExprCallableType[_T]
) -> hybrid_property[_T]:
"""Provide a modifying decorator that defines a SQL-expression
producing method.
When a hybrid is invoked at the class level, the SQL expression given
here is wrapped inside of a specialized :class:`.QueryableAttribute`,
which is the same kind of object used by the ORM to represent other
mapped attributes. The reason for this is so that other class-level
attributes such as docstrings and a reference to the hybrid itself may
be maintained within the structure that's returned, without any
modifications to the original SQL expression passed in.
.. note::
When referring to a hybrid property from an owning class (e.g.
``SomeClass.some_hybrid``), an instance of
:class:`.QueryableAttribute` is returned, representing the
expression or comparator object as well as this hybrid object.
However, that object itself has accessors called ``expression`` and
``comparator``; so when attempting to override these decorators on a
subclass, it may be necessary to qualify it using the
:attr:`.hybrid_property.overrides` modifier first. See that
modifier for details.
.. seealso::
:ref:`hybrid_distinct_expression`
"""
return self._copy(expr=expr)
def comparator(
self, comparator: _HybridComparatorCallableType[_T]
) -> hybrid_property[_T]:
"""Provide a modifying decorator that defines a custom
comparator producing method.
The return value of the decorated method should be an instance of
:class:`~.hybrid.Comparator`.
.. note:: The :meth:`.hybrid_property.comparator` decorator
**replaces** the use of the :meth:`.hybrid_property.expression`
decorator. They cannot be used together.
When a hybrid is invoked at the class level, the
:class:`~.hybrid.Comparator` object given here is wrapped inside of a
specialized :class:`.QueryableAttribute`, which is the same kind of
object used by the ORM to represent other mapped attributes. The
reason for this is so that other class-level attributes such as
docstrings and a reference to the hybrid itself may be maintained
within the structure that's returned, without any modifications to the
original comparator object passed in.
.. note::
When referring to a hybrid property from an owning class (e.g.
``SomeClass.some_hybrid``), an instance of
:class:`.QueryableAttribute` is returned, representing the
expression or comparator object as this hybrid object. However,
that object itself has accessors called ``expression`` and
``comparator``; so when attempting to override these decorators on a
subclass, it may be necessary to qualify it using the
:attr:`.hybrid_property.overrides` modifier first. See that
modifier for details.
"""
return self._copy(custom_comparator=comparator)
def update_expression(
self, meth: _HybridUpdaterType[_T]
) -> hybrid_property[_T]:
"""Provide a modifying decorator that defines an UPDATE tuple
producing method.
The method accepts a single value, which is the value to be
rendered into the SET clause of an UPDATE statement. The method
should then process this value into individual column expressions
that fit into the ultimate SET clause, and return them as a
sequence of 2-tuples. Each tuple
contains a column expression as the key and a value to be rendered.
E.g.::
class Person(Base):
# ...
first_name = Column(String)
last_name = Column(String)
@hybrid_property
def fullname(self):
return first_name + " " + last_name
@fullname.update_expression
def fullname(cls, value):
fname, lname = value.split(" ", 1)
return [
(cls.first_name, fname),
(cls.last_name, lname)
]
.. versionadded:: 1.2
"""
return self._copy(update_expr=meth)
@util.memoized_property
def _expr_comparator(
self,
) -> Callable[[Any], _HybridClassLevelAccessor[_T]]:
if self.custom_comparator is not None:
return self._get_comparator(self.custom_comparator)
elif self.expr is not None:
return self._get_expr(self.expr)
else:
return self._get_expr(cast(_HybridExprCallableType[_T], self.fget))
def _get_expr(
self, expr: _HybridExprCallableType[_T]
) -> Callable[[Any], _HybridClassLevelAccessor[_T]]:
def _expr(cls: Any) -> ExprComparator[_T]:
return ExprComparator(cls, expr(cls), self)
util.update_wrapper(_expr, expr)
return self._get_comparator(_expr)
def _get_comparator(
self, comparator: Any
) -> Callable[[Any], _HybridClassLevelAccessor[_T]]:
proxy_attr = attributes.create_proxied_attribute(self)
def expr_comparator(
owner: Type[object],
) -> _HybridClassLevelAccessor[_T]:
# because this is the descriptor protocol, we don't really know
# what our attribute name is. so search for it through the
# MRO.
for lookup in owner.__mro__:
if self.__name__ in lookup.__dict__:
if lookup.__dict__[self.__name__] is self:
name = self.__name__
break
else:
name = attributes._UNKNOWN_ATTR_KEY # type: ignore[assignment]
return cast(
"_HybridClassLevelAccessor[_T]",
proxy_attr(
owner,
name,
self,
comparator(owner),
doc=comparator.__doc__ or self.__doc__,
),
)
return expr_comparator
class Comparator(interfaces.PropComparator[_T]):
"""A helper class that allows easy construction of custom
:class:`~.orm.interfaces.PropComparator`
classes for usage with hybrids."""
def __init__(
self, expression: Union[_HasClauseElement[_T], SQLColumnExpression[_T]]
):
self.expression = expression
def __clause_element__(self) -> roles.ColumnsClauseRole:
expr = self.expression
if is_has_clause_element(expr):
ret_expr = expr.__clause_element__()
else:
if TYPE_CHECKING:
assert isinstance(expr, ColumnElement)
ret_expr = expr
if TYPE_CHECKING:
# see test_hybrid->test_expression_isnt_clause_element
# that exercises the usual place this is caught if not
# true
assert isinstance(ret_expr, ColumnElement)
return ret_expr
@util.non_memoized_property
def property(self) -> interfaces.MapperProperty[_T]:
raise NotImplementedError()
def adapt_to_entity(
self, adapt_to_entity: AliasedInsp[Any]
) -> Comparator[_T]:
# interesting....
return self
class ExprComparator(Comparator[_T]):
def __init__(
self,
cls: Type[Any],
expression: Union[_HasClauseElement[_T], SQLColumnExpression[_T]],
hybrid: hybrid_property[_T],
):
self.cls = cls
self.expression = expression
self.hybrid = hybrid
def __getattr__(self, key: str) -> Any:
return getattr(self.expression, key)
@util.ro_non_memoized_property
def info(self) -> _InfoType:
return self.hybrid.info
def _bulk_update_tuples(
self, value: Any
) -> Sequence[Tuple[_DMLColumnArgument, Any]]:
if isinstance(self.expression, attributes.QueryableAttribute):
return self.expression._bulk_update_tuples(value)
elif self.hybrid.update_expr is not None:
return self.hybrid.update_expr(self.cls, value)
else:
return [(self.expression, value)]
@util.non_memoized_property
def property(self) -> MapperProperty[_T]:
# this accessor is not normally used, however is accessed by things
# like ORM synonyms if the hybrid is used in this context; the
# .property attribute is not necessarily accessible
return self.expression.property # type: ignore
def operate(
self, op: OperatorType, *other: Any, **kwargs: Any
) -> ColumnElement[Any]:
return op(self.expression, *other, **kwargs)
def reverse_operate(
self, op: OperatorType, other: Any, **kwargs: Any
) -> ColumnElement[Any]:
return op(other, self.expression, **kwargs) # type: ignore