Hybrid Attributes¶
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))
{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 Select.filter_by()
are supported
with hybrid attributes as well:
>>> 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
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)))
{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}
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 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 Using inplace to create pep-484 compliant hybrid properties.
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
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))
{printsql}SELECT interval.id, interval.start, interval."end"
FROM interval
WHERE abs(interval."end" - interval.start) / :abs_1 > :param_1
Using inplace
to create pep-484 compliant hybrid properties¶
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 referred towards 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 Reusing Hybrid Properties across Subclasses 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.
New in version 2.0.4: 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.
Defining Setters¶
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
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 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}))
{printsql}UPDATE interval SET "end"=(interval.start + :start_1)
This SET expression is accommodated by the ORM automatically.
See also
ORM-Enabled INSERT, UPDATE, and DELETE statements - 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
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))
{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:
>>> 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
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 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"))
{printsql}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,
)
Reusing Hybrid Properties across Subclasses¶
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)
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):
>>> 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:
>>> 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.
See also
Hybrids and Value Agnostic Types - on the techspot.zzzeek.org blog
Value Agnostic Types, Part II - on the techspot.zzzeek.org blog
API Reference¶
Object Name | Description |
---|---|
A helper class that allows easy construction of custom
|
|
A decorator which allows definition of a Python object method with both instance-level and class-level behavior. |
|
A decorator which allows definition of a Python descriptor with both instance-level and class-level behavior. |
|
An enumeration. |
- 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: Optional[Callable[[Concatenate[Any, _P]], SQLCoreOperations[_R]]] = 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
-
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 thehybrid_method.expression()
decorator is called, so this attribute returns Self.New in version 2.0.4.
-
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 aMapperProperty
. But can also be an extension type such asAssociationProxy
orhybrid_property
. TheInspectionAttr.extension_type
will refer to a constant identifying the specific subtype.See also
-
method
- 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: 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
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
.Note
The
hybrid_property.comparator()
decorator replaces the use of thehybrid_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 specializedQueryableAttribute
, 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 ofQueryableAttribute
is returned, representing the expression or comparator object as this hybrid object. However, that object itself has accessors calledexpression
andcomparator
; so when attempting to override these decorators on a subclass, it may be necessary to qualify it using thehybrid_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.Note
When referring to a hybrid property from an owning class (e.g.
SomeClass.some_hybrid
), an instance ofQueryableAttribute
is returned, representing the expression or comparator object as well as this hybrid object. However, that object itself has accessors calledexpression
andcomparator
; so when attempting to override these decorators on a subclass, it may be necessary to qualify it using thehybrid_property.overrides
modifier first. See that modifier for details.
-
attribute
sqlalchemy.ext.hybrid.hybrid_property.
extension_type: InspectionAttrExtensionType = 'HYBRID_PROPERTY'¶ The extension type, if any. Defaults to
NotExtension.NOT_EXTENSION
-
method
sqlalchemy.ext.hybrid.hybrid_property.
getter(fget: _HybridGetterType[_T]) hybrid_property[_T] ¶ Provide a modifying decorator that defines a getter method.
New in version 1.2.
-
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)
New in version 2.0.4.
-
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 aMapperProperty
. But can also be an extension type such asAssociationProxy
orhybrid_property
. TheInspectionAttr.extension_type
will refer to a constant identifying the specific subtype.See also
-
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 likehybrid_property.expression()
andhybrid_property.comparator()
to be used without conflicting with the same-named attributes normally present on theQueryableAttribute
: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)
New in version 1.2.
-
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) ]
New in version 1.2.
-
method
- 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¶
An enumeration.
Members
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 typehybrid_method
.Is assigned to the
InspectionAttr.extension_type
attribute.See also
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.See also
Mapper.all_orm_attributes
- Symbol indicating an
-
attribute