混合属性

Hybrid Attributes

中文

定义具有“混合”行为的 ORM 映射类属性。

“混合”意味着属性在类级别和实例级别具有不同的行为。

hybrid 扩展提供了一种特殊形式的方法装饰器，并且对 SQLAlchemy 其余部分的依赖最小化。其基本操作理论可以与任何基于描述符的表达式系统一起工作。

考虑一个映射 Interval，表示整数的 start 和 end 值。我们可以在映射类上定义更高层次的函数，这些函数在类级别生成 SQL 表达式，在实例级别进行 Python 表达式求值。下面，使用 hybrid_method 或 hybrid_property 装饰的每个函数可以接收 self 作为类的实例，或者根据上下文直接接收类本身:

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)

上面的 length 属性返回 end 和 start 属性之间的差值。对于 Interval 实例，这个减法操作在 Python 中进行，使用常规的 Python 描述符机制:

>>> i1 = Interval(5, 10)
>>> i1.length
5

当处理 Interval 类本身时，hybrid_property 描述符根据 Interval 类作为参数来求值函数体，当使用 SQLAlchemy 表达式机制求值时，返回一个新的 SQL 表达式：

>>> from sqlalchemy import select
>>> print(select(Interval.length))
SELECT interval."end" - interval.start AS length
FROM interval
>>> print(select(Interval).filter(Interval.length > 10))
SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval."end" - interval.start > :param_1

使用混合属性时，像 Select.filter_by() 这样的过滤方法也得到了支持：

>>> print(select(Interval).filter_by(length=5))
SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval."end" - interval.start = :param_1

Interval 类示例还展示了两个方法，contains() 和 intersects()，它们都使用 hybrid_method 装饰器。这个装饰器将同样的思想应用于方法，正如 hybrid_property 对属性所做的那样。这些方法返回布尔值，并利用 Python 的 | 和 & 位运算符来生成等效的实例级和 SQL 表达式级布尔行为：

>>> 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)))
SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval.start <= :start_1 AND interval."end" > :end_1
>>> ia = aliased(Interval)
>>> print(select(Interval, ia).filter(Interval.intersects(ia)))
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"

英文

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 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 hybrid_method or 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 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:

>>> from sqlalchemy import select
>>> print(select(Interval.length))
SELECT interval."end" - interval.start AS length
FROM interval
>>> print(select(Interval).filter(Interval.length > 10))
SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval."end" - interval.start > :param_1

Filtering methods such as Select.filter_by() are supported with hybrid attributes as well:

>>> print(select(Interval).filter_by(length=5))
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 hybrid_method. This decorator applies the same idea to methods that 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:

>>> 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)))
SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE interval.start <= :start_1 AND interval."end" > :end_1
>>> ia = aliased(Interval)
>>> print(select(Interval, ia).filter(Interval.intersects(ia)))
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"

定义不同于属性行为的表达式行为

Defining Expression Behavior Distinct from Attribute Behavior

中文

在前一节中，我们在 Interval.contains 和 Interval.intersects 方法中使用 & 和 | 位运算符时是幸运的，因为我们的函数操作的是两个布尔值，并返回一个新的布尔值。在许多情况下，Python 函数和 SQLAlchemy SQL 表达式的构造之间有足够的差异，因此应该定义两个独立的 Python 表达式。hybrid 装饰器定义了一个 修饰符 hybrid_property.expression() 用于此目的。作为示例，我们将定义区间的半径，这需要使用绝对值函数:

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)

在上面的示例中，首先将 hybrid_property 分配给 Interval.radius，然后通过名为 Interval._radius_expression 的后续方法进行修改，该方法使用装饰器 @radius.inplace.expression，将两个修饰符 hybrid_property.inplace 和 hybrid_property.expression 链接在一起。使用 hybrid_property.inplace 表明 hybrid_property.expression() 修饰符应直接修改现有的混合对象 Interval.radius，而不是创建一个新对象。关于这个修饰符及其原因的讨论将在下一节 使用“inplace”创建符合 pep-484 的混合属性 中讨论。使用 @classmethod 是可选的，严格来说，它只是为了给类型工具一个提示，表明 cls 在这种情况下应该是 Interval 类，而不是 Interval 的实例。

备注

hybrid_property.inplace 以及为正确的类型支持而使用 @classmethod，自 SQLAlchemy 2.0.4 起可用，早期版本不支持。

现在，Interval.radius 包含了一个表达式元素，当在类级别访问 Interval.radius 时，SQL 函数 ABS() 被返回：

>>> from sqlalchemy import select
>>> print(select(Interval).filter(Interval.radius > 5))
SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE abs(interval."end" - interval.start) / :abs_1 > :param_1

英文

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 hybrid decorator defines a modifier 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 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 hybrid_property.inplace and hybrid_property.expression. The use of hybrid_property.inplace indicates that the 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 使用“inplace”创建符合 pep-484 的混合属性. 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.

备注

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:

>>> from sqlalchemy import select
>>> print(select(Interval).filter(Interval.radius > 5))
SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE abs(interval."end" - interval.start) / :abs_1 > :param_1

使用“inplace”创建符合 pep-484 的混合属性

Using inplace to create pep-484 compliant hybrid properties

中文

在前一节中，展示了一个 hybrid_property 装饰器，其中包括两个独立的方法级函数，它们都被装饰以生成一个名为 Interval.radius 的单一对象属性。实际上，我们可以为 hybrid_property 使用几种不同的修饰符，包括 hybrid_property.expression()、hybrid_property.setter() 和 hybrid_property.update_expression()。

SQLAlchemy 的 hybrid_property 装饰器的设计目的是，像 Python 内建的 @property 装饰器一样，可以重复定义属性，每次使用 相同的属性名，就像下面的示例展示了如何使用 hybrid_property.setter() 和 hybrid_property.expression() 来修饰 Interval.radius 描述符:

# 正确使用，但不被 pep-484 工具接受


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)

如上所示，存在三个 Interval.radius 方法，但由于每个方法都被装饰，首先使用 hybrid_property 装饰器，然后使用 @radius 名称本身，最终效果是 Interval.radius 是一个包含三个不同功能的单一属性。此使用风格源自 Python 文档中的 @property 用法 <https://docs.python.org/3/library/functions.html#property>_。 需要注意的是，由于 @property 和 hybrid_property 的工作原理，每次都会 创建描述符的副本 。也就是说，每次调用 @radius.expression、@radius.setter 等时，都会完全创建一个新对象。这使得可以在子类中重新定义属性，而不会出现问题（有关如何使用此方法，请参见本节后面的 跨子类重用混合属性）。

然而，上述方法与类型工具（如 mypy 和 pyright）不兼容。Python 自己的 @property 装饰器没有这个限制，仅仅因为 这些工具硬编码了 @property 的行为，这意味着 SQLAlchemy 在 PEP 484 合规性下无法使用此语法。

为了在保持类型合规的同时生成合理的语法，hybrid_property.inplace 装饰器允许使用不同的方法名称重新使用相同的装饰器，同时仍然生成一个单一的装饰器:

# 正确使用，且被 pep-484 工具接受


class Interval(Base):
    # ...

    @hybrid_property
    def radius(self) -> float:
        return abs(self.length) / 2

    @radius.inplace.setter
    def _radius_setter(self, value: float) -> None:
        # 仅为示例
        self.length = value * 2

    @radius.inplace.expression
    @classmethod
    def _radius_expression(cls) -> ColumnElement[float]:
        return type_coerce(func.abs(cls.length) / 2, Float)

使用 hybrid_property.inplace 进一步限定了装饰器的使用，即不应创建新副本，从而保持 Interval.radius 名称，同时允许 Interval._radius_setter 和 Interval._radius_expression 使用不同的名称。

在 2.0.4 版本加入: 增加了 hybrid_property.inplace，允许更简洁地构建复合的 hybrid_property 对象，而无需重复使用方法名称。同时，允许在 hybrid_property.expression、hybrid_property.update_expression 和 hybrid_property.comparator 中使用 @classmethod，使得类型工具能够在方法签名中识别 cls 为类而非实例。

英文

In the previous section, a 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 hybrid_property including hybrid_property.expression(), hybrid_property.setter() and hybrid_property.update_expression().

SQLAlchemy’s 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 hybrid_property.setter() and 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 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. It is important to note that the way both @property as well as 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 跨子类重用混合属性 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, meaning this syntax is not available to SQLAlchemy under PEP 484 compliance.

In order to produce a reasonable syntax while remaining typing compliant, the 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 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.

在 2.0.4 版本加入: Added hybrid_property.inplace to allow less verbose construction of composite hybrid_property objects while not having to use repeated method names. Additionally allowed the use of @classmethod within hybrid_property.expression, hybrid_property.update_expression, and hybrid_property.comparator to allow typing tools to identify cls as a class and not an instance in the method signature.

定义 Setter

Defining Setters

中文

hybrid_property.setter() 修饰符允许构建自定义的 setter 方法，用于修改对象上的值:

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

现在，当设置属性时，会调用 length(self, value) 方法:

>>> i1 = Interval(5, 10)
>>> i1.length
5
>>> i1.length = 12
>>> i1.end
17

英文

The 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

允许批量 ORM 更新

Allowing Bulk ORM Update

中文

混合属性可以定义一个用于 ORM 启用的更新操作的自定义 “UPDATE” 处理器，从而允许混合属性在更新语句的 SET 子句中使用。

通常，当混合属性与 update() 一起使用时，其 SQL 表达式会作为 SET 子句中目标列的替代。如果我们的 Interval 类中有一个名为 start_point 的混合属性，关联到 Interval.start，那么它可以被直接替代使用:

from sqlalchemy import update

stmt = update(Interval).values({Interval.start_point: 10})

然而，当使用像 Interval.length 这样的复合混合属性时，该混合属性代表多个列。我们可以设置一个处理器来处理传入 VALUES 表达式中的值，该值会影响这些列，这可以通过 hybrid_property.update_expression() 装饰器来实现。一个与我们 setter 类似的处理器可以这样定义:

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)]

如上所示，如果我们在 UPDATE 表达式中使用 Interval.length，我们会得到一个混合的 SET 表达式：

>>> from sqlalchemy import update
>>> print(update(Interval).values({Interval.length: 25}))
UPDATE interval SET "end"=(interval.start + :start_1)

这个 SET 表达式会被 ORM 自动处理。

参见

启用 ORM 的 INSERT、UPDATE 和 DELETE 语句 - 包含关于 ORM 启用的 UPDATE 语句的背景信息

英文

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 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 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:

>>> from sqlalchemy import update
>>> print(update(Interval).values({Interval.length: 25}))
UPDATE interval SET "end"=(interval.start + :start_1)

This SET expression is accommodated by the ORM automatically.

参见

启用 ORM 的 INSERT、UPDATE 和 DELETE 语句 - includes background on ORM-enabled UPDATE statements

使用关系

Working with Relationships

中文

在创建适用于关联对象的混合属性时，与基于列的数据相比，没有本质的区别。不过，对于这些混合属性，通常更需要使用不同的表达式。我们将说明的两种变体是“依赖连接（join-dependent）”的混合属性和“相关子查询（correlated subquery）”的混合属性。

英文

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.

连接依赖关系混合

Join-Dependent Relationship Hybrid

中文

来看如下的声明式映射，它将 User 和 SavingsAccount 关联起来:

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,
        )

上述混合属性 balance 处理的是该用户账户列表中的第一个 SavingsAccount 条目。 在 Python 层的 getter/setter 方法中，可以将 accounts 当作存在于 self 上的 Python 列表来操作。

小技巧

上例中的 User.balance getter 会访问 self.accounts 集合，而该集合通常通过在 User.balance 上配置的 relationship() 使用 selectinload() 加载策略来加载。如果在 relationship() 上未显式指定加载策略，默认策略为 lazyload()，它会按需发出 SQL 查询。在使用 asyncio 时，不支持按需加载器（如 lazyload()），因此在使用 asyncio 时应注意确保该混合访问器可以访问 self.accounts 集合。

在表达式层面，期望 User 类在使用时有合适的上下文，即会存在与 SavingsAccount 的合适连接：

>>> from sqlalchemy import select
>>> print(
...     select(User, User.balance)
...     .join(User.accounts)
...     .filter(User.balance > 5000)
... )
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

但需要注意的是，虽然在实例层级的访问器中需要担心 self.accounts 是否存在，而在 SQL 表达式层中，这一问题以另一种方式体现，即我们通常会使用外连接：

>>> from sqlalchemy import select
>>> from sqlalchemy import or_
>>> print(
...     select(User, User.balance)
...     .outerjoin(User.accounts)
...     .filter(or_(User.balance < 5000, User.balance == None))
... )
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

英文

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.

小技巧

The User.balance getter in the above example accesses the self.acccounts collection, which will normally be loaded via the selectinload() loader strategy configured on the User.balance relationship(). The default loader strategy when not otherwise stated on relationship() is lazyload(), which emits SQL on demand. When using asyncio, on-demand loaders such as 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:

>>> from sqlalchemy import select
>>> print(
...     select(User, User.balance)
...     .join(User.accounts)
...     .filter(User.balance > 5000)
... )
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:

>>> from sqlalchemy import select
>>> from sqlalchemy import or_
>>> print(
...     select(User, User.balance)
...     .outerjoin(User.accounts)
...     .filter(or_(User.balance < 5000, User.balance == None))
... )
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

相关子查询关系混合

Correlated Subquery Relationship Hybrid

中文

当然，我们也可以选择不依赖外部查询中的连接用法，而是使用相关子查询，它可以更便捷地封装进单个列表达式中。相关子查询更具可移植性，但在 SQL 层通常性能较差。借助 使用 column_property 中展示的技术，我们可以调整 SavingsAccount 示例，使其聚合 所有 账户的余额，并为列表达式使用相关子查询:

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")
        )

上述方法会为我们生成 balance 列，该列渲染为一个相关 SELECT 子查询：

>>> from sqlalchemy import select
>>> print(select(User).filter(User.balance > 400))
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

英文

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 使用 column_property, 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:

>>> from sqlalchemy import select
>>> print(select(User).filter(User.balance > 400))
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

构建自定义比较器

Building Custom Comparators

中文

混合属性还包括一个辅助功能，允许构建自定义比较器（comparator）。比较器对象允许对每一个 SQLAlchemy 表达式操作符的行为进行单独定制。它们在创建在 SQL 端具有高度特殊行为的自定义类型时非常有用。

备注

本节引入的 hybrid_property.comparator() 装饰器 替代 了 hybrid_property.expression() 装饰器。两者不能同时使用。

下面的示例类允许对名为 word_insensitive 的属性进行不区分大小写的比较:

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)

如上所示，针对 word_insensitive 的 SQL 表达式将在两边应用 LOWER() SQL 函数：

>>> from sqlalchemy import select
>>> print(select(SearchWord).filter_by(word_insensitive="Trucks"))
SELECT searchword.id, searchword.word
FROM searchword
WHERE lower(searchword.word) = lower(:lower_1)

上面的 CaseInsensitiveComparator 实现了部分 ColumnOperators 接口。可以使用 Operators.operate() 对所有比较操作（如 eq、lt、gt 等）统一应用小写转换操作:

class CaseInsensitiveComparator(Comparator):
    def operate(self, op, other, **kwargs):
        return op(
            func.lower(self.__clause_element__()),
            func.lower(other),
            **kwargs,
        )

英文

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.

备注

The hybrid_property.comparator() decorator introduced in this section replaces the use of the 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:

>>> from sqlalchemy import select
>>> print(select(SearchWord).filter_by(word_insensitive="Trucks"))
SELECT searchword.id, searchword.word
FROM searchword
WHERE lower(searchword.word) = lower(:lower_1)

The CaseInsensitiveComparator above implements part of the ColumnOperators interface. A “coercion” operation like lowercasing can be applied to all comparison operations (i.e. eq, lt, gt, etc.) using Operators.operate():

class CaseInsensitiveComparator(Comparator):
    def operate(self, op, other, **kwargs):
        return op(
            func.lower(self.__clause_element__()),
            func.lower(other),
            **kwargs,
        )

跨子类重用混合属性

Reusing Hybrid Properties across Subclasses

中文

混合属性可以从超类中引用，从而允许通过 hybrid_property.getter()、hybrid_property.setter() 等方法在子类中重新定义这些方法。这类似于 Python 标准的 @property 对象的工作方式:

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]

    # 这里没有使用 'inplace'；调用 getter 创建了 FirstNameOnly.name 的副本，
    # 该副本仅属于 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)

如上所示，FirstNameLastName 类引用 FirstNameOnly.name 混合属性，以重用其 getter 和 setter 方法。

当仅重写 hybrid_property.expression() 和 hybrid_property.comparator() 且首次引用的是超类时，这些名称会与类级的 QueryableAttribute 对象中的同名访问器发生冲突。要在直接引用父类描述符时重写这些方法，需要添加特殊限定符 hybrid_property.overrides，该限定符会将已注入的属性反引用为混合对象:

class FirstNameLastName(FirstNameOnly):
    # ...

    last_name: Mapped[str]

    @FirstNameOnly.name.overrides.expression
    @classmethod
    def name(cls):
        return func.concat(cls.first_name, " ", cls.last_name)

英文

A hybrid can be referred to from a superclass, to allow modifying methods like hybrid_property.getter(), 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 hybrid_property.expression() and hybrid_property.comparator() alone as the first reference to the superclass, these names conflict with the same-named accessors on the class- level QueryableAttribute object returned at the class level. To override these methods when referring directly to the parent class descriptor, add the special qualifier 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)

混合值对象

Hybrid Value Objects

中文

注意在前面的例子中，如果我们将 SearchWord 实例的 word_insensitive 属性与普通 Python 字符串进行比较，普通字符串不会被转换为小写 —— 我们构建的 CaseInsensitiveComparator 只应用于 SQL 层，因为它是由 @word_insensitive.comparator 返回的。

更全面的自定义比较器形式是构建一个 混合值对象（Hybrid Value Object）。这种技术将目标值或表达式应用于一个值对象，并在所有情况下由访问器返回该对象。值对象可以控制值上的所有操作，以及比较值的处理方式，无论是在 SQL 表达式端还是 Python 值端。以下使用新的 CaseInsensitiveWord 类替换之前的 CaseInsensitiveComparator 类:

class CaseInsensitiveWord(Comparator):
    "混合值，表示单词的小写表示形式。"

    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"
    "应用于 Query 元组结果的标签"

如上所示，CaseInsensitiveWord 对象表示 self.word，该值可能是一个 SQL 函数，也可能是一个原生 Python 值。通过重写 operate() 和 __clause_element__() 来处理 self.word，可以使所有比较操作适用于转换后的 word，无论是在 SQL 端还是 Python 端。我们的 SearchWord 类现在可以始终通过一个混合调用无条件地返回 CaseInsensitiveWord 对象:

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)

现在， word_insensitive 属性具有统一的不区分大小写比较行为，包括 SQL 表达式与 Python 表达式之间的比较（注意此处 Python 值已在 Python 层被转换为小写）：

>>> print(select(SearchWord).filter_by(word_insensitive="Trucks"))
SELECT searchword.id AS searchword_id, searchword.word AS searchword_word
FROM searchword
WHERE lower(searchword.word) = :lower_1

SQL 表达式对 SQL 表达式：

>>> 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
...     )
... )
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)

仅 Python 表达式:

>>> ws1 = SearchWord(word="SomeWord")
>>> ws1.word_insensitive == "sOmEwOrD"
True
>>> ws1.word_insensitive == "XOmEwOrX"
False
>>> print(ws1.word_insensitive)
someword

混合值模式对任何可能具有多种表示形式的值都非常有用，比如时间戳、时间差、度量单位、货币和加密密码等。

参见

Hybrids and Value Agnostic Types - 见 techspot.zzzeek.org 博客

Value Agnostic Types, Part II - 见 techspot.zzzeek.org 博客

英文

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):

>>> print(select(SearchWord).filter_by(word_insensitive="Trucks"))
SELECT searchword.id AS searchword_id, searchword.word AS searchword_word
FROM searchword
WHERE lower(searchword.word) = :lower_1

SQL expression versus SQL expression:

>>> 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
...     )
... )
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.

参见

Hybrids and Value Agnostic Types - on the techspot.zzzeek.org blog

Value Agnostic Types, Part II - on the techspot.zzzeek.org blog

API 参考

API Reference

Object Name	Description
Comparator	A helper class that allows easy construction of custom PropComparator classes for usage with hybrids.
hybrid_method	A decorator which allows definition of a Python object method with both instance-level and class-level behavior.
hybrid_property	A decorator which allows definition of a Python descriptor with both instance-level and class-level behavior.
HybridExtensionType

class sqlalchemy.ext.hybrid.hybrid_method

A decorator which allows definition of a Python object method with both instance-level and class-level behavior.

Members

__init__(), expression(), extension_type, inplace, is_attribute

Class signature

class sqlalchemy.ext.hybrid.hybrid_method (sqlalchemy.orm.base.InspectionAttrInfo, typing.Generic)

method sqlalchemy.ext.hybrid.hybrid_method.__init__(func: Callable[[Concatenate[Any, _P]], _R], expr: Callable[[Concatenate[Any, _P]], SQLCoreOperations[_R]] | None = None)

Create a new 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)

method sqlalchemy.ext.hybrid.hybrid_method.expression(expr: Callable[[Concatenate[Any, _P]], SQLCoreOperations[_R]]) → hybrid_method[_P, _R]

Provide a modifying decorator that defines a SQL-expression producing method.

attribute sqlalchemy.ext.hybrid.hybrid_method.extension_type: InspectionAttrExtensionType = 'HYBRID_METHOD'

The extension type, if any. Defaults to NotExtension.NOT_EXTENSION

参见

HybridExtensionType

AssociationProxyExtensionType

attribute sqlalchemy.ext.hybrid.hybrid_method.inplace

Return the inplace mutator for this hybrid_method.

The hybrid_method class already performs “in place” mutation when the hybrid_method.expression() decorator is called, so this attribute returns Self.

在 2.0.4 版本加入.

参见

使用“inplace”创建符合 pep-484 的混合属性

attribute sqlalchemy.ext.hybrid.hybrid_method.is_attribute = True

True if this object is a Python descriptor.

This can refer to one of many types. Usually a QueryableAttribute which handles attributes events on behalf of a MapperProperty. But can also be an extension type such as AssociationProxy or hybrid_property. The InspectionAttr.extension_type will refer to a constant identifying the specific subtype.

参见

Mapper.all_orm_descriptors

class sqlalchemy.ext.hybrid.hybrid_property

A decorator which allows definition of a Python descriptor with both instance-level and class-level behavior.

Members

__init__(), comparator(), deleter(), expression(), extension_type, getter(), inplace, is_attribute, overrides, setter(), update_expression()

Class signature

class sqlalchemy.ext.hybrid.hybrid_property (sqlalchemy.orm.base.InspectionAttrInfo, sqlalchemy.orm.base.ORMDescriptor)

method sqlalchemy.ext.hybrid.hybrid_property.__init__(fget: _HybridGetterType[_T], fset: _HybridSetterType[_T] | None = None, fdel: _HybridDeleterType[_T] | None = None, expr: _HybridExprCallableType[_T] | None = None, custom_comparator: Comparator[_T] | None = None, update_expr: _HybridUpdaterType[_T] | None = None)

Create a new 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

method sqlalchemy.ext.hybrid.hybrid_property.comparator(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 Comparator.

备注

The hybrid_property.comparator() decorator replaces the use of the hybrid_property.expression() decorator. They cannot be used together.

When a hybrid is invoked at the class level, the Comparator object given here is wrapped inside of a specialized 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.

备注

When referring to a hybrid property from an owning class (e.g. SomeClass.some_hybrid), an instance of 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 hybrid_property.overrides modifier first. See that modifier for details.

method sqlalchemy.ext.hybrid.hybrid_property.deleter(fdel: _HybridDeleterType[_T]) → hybrid_property[_T]

Provide a modifying decorator that defines a deletion method.

method sqlalchemy.ext.hybrid.hybrid_property.expression(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 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.

备注

When referring to a hybrid property from an owning class (e.g. SomeClass.some_hybrid), an instance of 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 hybrid_property.overrides modifier first. See that modifier for details.

参见

定义不同于属性行为的表达式行为

attribute sqlalchemy.ext.hybrid.hybrid_property.extension_type: InspectionAttrExtensionType = 'HYBRID_PROPERTY'

The extension type, if any. Defaults to NotExtension.NOT_EXTENSION

参见

HybridExtensionType

AssociationProxyExtensionType

method sqlalchemy.ext.hybrid.hybrid_property.getter(fget: _HybridGetterType[_T]) → hybrid_property[_T]

Provide a modifying decorator that defines a getter method.

attribute sqlalchemy.ext.hybrid.hybrid_property.inplace

Return the inplace mutator for this 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)

在 2.0.4 版本加入.

参见

使用“inplace”创建符合 pep-484 的混合属性

attribute sqlalchemy.ext.hybrid.hybrid_property.is_attribute = True

True if this object is a Python descriptor.

This can refer to one of many types. Usually a QueryableAttribute which handles attributes events on behalf of a MapperProperty. But can also be an extension type such as AssociationProxy or hybrid_property. The InspectionAttr.extension_type will refer to a constant identifying the specific subtype.

参见

Mapper.all_orm_descriptors

attribute sqlalchemy.ext.hybrid.hybrid_property.overrides

Prefix for a method that is overriding an existing attribute.

The 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 hybrid_property.expression() and hybrid_property.comparator() to be used without conflicting with the same-named attributes normally present on the 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)

参见

跨子类重用混合属性

method sqlalchemy.ext.hybrid.hybrid_property.setter(fset: _HybridSetterType[_T]) → hybrid_property[_T]

Provide a modifying decorator that defines a setter method.

method sqlalchemy.ext.hybrid.hybrid_property.update_expression(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)]

class sqlalchemy.ext.hybrid.Comparator

A helper class that allows easy construction of custom PropComparator classes for usage with hybrids.

Class signature

class sqlalchemy.ext.hybrid.Comparator (sqlalchemy.orm.PropComparator)

class sqlalchemy.ext.hybrid.HybridExtensionType

Members

HYBRID_METHOD, HYBRID_PROPERTY

Class signature

class sqlalchemy.ext.hybrid.HybridExtensionType (sqlalchemy.orm.base.InspectionAttrExtensionType)

attribute sqlalchemy.ext.hybrid.HybridExtensionType.HYBRID_METHOD = 'HYBRID_METHOD'

Symbol indicating an InspectionAttr that’s of type hybrid_method.

Is assigned to the InspectionAttr.extension_type attribute.

参见

Mapper.all_orm_attributes

attribute sqlalchemy.ext.hybrid.HybridExtensionType.HYBRID_PROPERTY = 'HYBRID_PROPERTY'

Symbol indicating an InspectionAttr that’s

of type hybrid_method.

Is assigned to the InspectionAttr.extension_type attribute.

参见

Mapper.all_orm_attributes