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# ext/hybrid.py
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
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, is around 50 lines of code and has almost no
dependencies on the rest of SQLAlchemy. It can, in theory, 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
as the class itself::
from sqlalchemy import Column, Integer
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import Session, aliased
from sqlalchemy.ext.hybrid import hybrid_property, hybrid_method
Base = declarative_base()
class Interval(Base):
__tablename__ = 'interval'
id = Column(Integer, primary_key=True)
start = Column(Integer, nullable=False)
end = Column(Integer, nullable=False)
def __init__(self, start, end):
self.start = start
self.end = end
@hybrid_property
def length(self):
return self.end - self.start
@hybrid_method
def contains(self, point):
return (self.start <= point) & (point <= self.end)
@hybrid_method
def intersects(self, other):
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
(here using the :attr:`.QueryableAttribute.expression` accessor)
returns a new SQL expression::
>>> print(Interval.length.expression)
interval."end" - interval.start
>>> print(Session().query(Interval).filter(Interval.length > 10))
SELECT interval.id AS interval_id, interval.start AS interval_start,
interval."end" AS interval_end
FROM interval
WHERE interval."end" - interval.start > :param_1
ORM methods such as :meth:`_query.Query.filter_by`
generally use ``getattr()`` to
locate attributes, so can also be used with hybrid attributes::
>>> print(Session().query(Interval).filter_by(length=5))
SELECT interval.id AS interval_id, interval.start AS interval_start,
interval."end" AS 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::
>>> i1.contains(6)
True
>>> i1.contains(15)
False
>>> i1.intersects(Interval(7, 18))
True
>>> i1.intersects(Interval(25, 29))
False
>>> print(Session().query(Interval).filter(Interval.contains(15)))
SELECT interval.id AS interval_id, interval.start AS interval_start,
interval."end" AS interval_end
FROM interval
WHERE interval.start <= :start_1 AND interval."end" > :end_1
>>> ia = aliased(Interval)
>>> print(Session().query(Interval, ia).filter(Interval.intersects(ia)))
SELECT interval.id AS interval_id, interval.start AS interval_start,
interval."end" AS 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"
.. _hybrid_distinct_expression:
Defining Expression Behavior Distinct from Attribute Behavior
--------------------------------------------------------------
Our usage of the ``&`` and ``|`` bitwise operators above 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` decorators define the
:meth:`.hybrid_property.expression` modifier 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 func
class Interval(object):
# ...
@hybrid_property
def radius(self):
return abs(self.length) / 2
@radius.expression
def radius(cls):
return func.abs(cls.length) / 2
Above the Python function ``abs()`` is used for instance-level
operations, the SQL function ``ABS()`` is used via the :data:`.func`
object for class-level expressions::
>>> i1.radius
2
>>> print(Session().query(Interval).filter(Interval.radius > 5))
SELECT interval.id AS interval_id, interval.start AS interval_start,
interval."end" AS interval_end
FROM interval
WHERE abs(interval."end" - interval.start) / :abs_1 > :param_1
.. note:: When defining an expression for a hybrid property or method, the
expression method **must** retain the name of the original hybrid, else
the new hybrid with the additional state will be attached to the class
with the non-matching name. To use the example above::
class Interval(object):
# ...
@hybrid_property
def radius(self):
return abs(self.length) / 2
# WRONG - the non-matching name will cause this function to be
# ignored
@radius.expression
def radius_expression(cls):
return func.abs(cls.length) / 2
This is also true for other mutator methods, such as
:meth:`.hybrid_property.update_expression`. This is the same behavior
as that of the ``@property`` construct that is part of standard Python.
Defining Setters
----------------
Hybrid properties can also define setter methods. If we wanted
``length`` above, when set, to modify the endpoint value::
class Interval(object):
# ...
@hybrid_property
def length(self):
return self.end - self.start
@length.setter
def length(self, value):
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 the
:meth:`_query.Query.update` method, allowing the hybrid to be used in the
SET clause of the update.
Normally, when using a hybrid with :meth:`_query.Query.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::
session.query(Interval).update({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 to :meth:`_query.Query.update` which can affect
this, using the :meth:`.hybrid_property.update_expression` decorator.
A handler that works similarly to our setter would be::
class Interval(object):
# ...
@hybrid_property
def length(self):
return self.end - self.start
@length.setter
def length(self, value):
self.end = self.start + value
@length.update_expression
def length(cls, value):
return [
(cls.end, cls.start + value)
]
Above, if we use ``Interval.length`` in an UPDATE expression as::
session.query(Interval).update(
{Interval.length: 25}, synchronize_session='fetch')
We'll get an UPDATE statement along the lines of::
UPDATE interval SET end=start + :value
In some cases, the default "evaluate" strategy can't perform the SET
expression in Python; while the addition operator we're using above
is supported, for more complex SET expressions it will usually be necessary
to use either the "fetch" or False synchronization strategy as illustrated
above.
.. versionadded:: 1.2 added support for bulk updates to hybrid properties.
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 sqlalchemy import Column, Integer, ForeignKey, Numeric, String
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.hybrid import hybrid_property
Base = declarative_base()
class SavingsAccount(Base):
__tablename__ = 'account'
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey('user.id'), nullable=False)
balance = Column(Numeric(15, 5))
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String(100), nullable=False)
accounts = relationship("SavingsAccount", backref="owner")
@hybrid_property
def balance(self):
if self.accounts:
return self.accounts[0].balance
else:
return None
@balance.setter
def balance(self, value):
if not self.accounts:
account = Account(owner=self)
else:
account = self.accounts[0]
account.balance = value
@balance.expression
def balance(cls):
return 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``.
However, 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::
>>> print(Session().query(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 or_
>>> print (Session().query(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
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 sqlalchemy import Column, Integer, ForeignKey, Numeric, String
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy import select, func
Base = declarative_base()
class SavingsAccount(Base):
__tablename__ = 'account'
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey('user.id'), nullable=False)
balance = Column(Numeric(15, 5))
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String(100), nullable=False)
accounts = relationship("SavingsAccount", backref="owner")
@hybrid_property
def balance(self):
return sum(acc.balance for acc in self.accounts)
@balance.expression
def balance(cls):
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::
>>> print(s.query(User).filter(User.balance > 400))
SELECT "user".id AS user_id, "user".name AS 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 sqlalchemy.ext.hybrid import Comparator, hybrid_property
from sqlalchemy import func, Column, Integer, String
from sqlalchemy.orm import Session
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class CaseInsensitiveComparator(Comparator):
def __eq__(self, other):
return func.lower(self.__clause_element__()) == func.lower(other)
class SearchWord(Base):
__tablename__ = 'searchword'
id = Column(Integer, primary_key=True)
word = Column(String(255), nullable=False)
@hybrid_property
def word_insensitive(self):
return self.word.lower()
@word_insensitive.comparator
def word_insensitive(cls):
return CaseInsensitiveComparator(cls.word)
Above, SQL expressions against ``word_insensitive`` will apply the ``LOWER()``
SQL function to both sides::
>>> print(Session().query(SearchWord).filter_by(word_insensitive="Trucks"))
SELECT searchword.id AS searchword_id, searchword.word AS 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):
return op(func.lower(self.__clause_element__()), func.lower(other))
.. _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 = Column(String)
@hybrid_property
def name(self):
return self.first_name
@name.setter
def name(self, value):
self.first_name = value
class FirstNameLastName(FirstNameOnly):
# ...
last_name = Column(String)
@FirstNameOnly.name.getter
def name(self):
return self.first_name + ' ' + self.last_name
@name.setter
def name(self, value):
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 = Column(String)
@FirstNameOnly.name.overrides.expression
def name(cls):
return func.concat(cls.first_name, ' ', cls.last_name)
.. versionadded:: 1.2 Added :meth:`.hybrid_property.getter` as well as the
ability to redefine accessors per-subclass.
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):
if not isinstance(other, CaseInsensitiveWord):
other = CaseInsensitiveWord(other)
return op(self.word, other.word)
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 = Column(Integer, primary_key=True)
word = Column(String(255), nullable=False)
@hybrid_property
def word_insensitive(self):
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(Session().query(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::
>>> sw1 = aliased(SearchWord)
>>> sw2 = aliased(SearchWord)
>>> print(Session().query(
... 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.
.. seealso::
`Hybrids and Value Agnostic Types
<http://techspot.zzzeek.org/2011/10/21/hybrids-and-value-agnostic-types/>`_
- on the techspot.zzzeek.org blog
`Value Agnostic Types, Part II
<http://techspot.zzzeek.org/2011/10/29/value-agnostic-types-part-ii/>`_ -
on the techspot.zzzeek.org blog
.. _hybrid_transformers:
Building Transformers
----------------------
A *transformer* is an object which can receive a :class:`_query.Query`
object and
return a new one. The :class:`_query.Query` object includes a method
:meth:`.with_transformation` that returns a new :class:`_query.Query`
transformed by
the given function.
We can combine this with the :class:`.Comparator` class to produce one type
of recipe which can both set up the FROM clause of a query as well as assign
filtering criterion.
Consider a mapped class ``Node``, which assembles using adjacency list into a
hierarchical tree pattern::
from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Node(Base):
__tablename__ = 'node'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('node.id'))
parent = relationship("Node", remote_side=id)
Suppose we wanted to add an accessor ``grandparent``. This would return the
``parent`` of ``Node.parent``. When we have an instance of ``Node``, this is
simple::
from sqlalchemy.ext.hybrid import hybrid_property
class Node(Base):
# ...
@hybrid_property
def grandparent(self):
return self.parent.parent
For the expression, things are not so clear. We'd need to construct a
:class:`_query.Query` where we :meth:`_query.Query.join` twice along
``Node.parent`` to get to the ``grandparent``. We can instead return a
transforming callable that we'll combine with the :class:`.Comparator` class to
receive any :class:`_query.Query` object, and return a new one that's joined to
the ``Node.parent`` attribute and filtered based on the given criterion::
from sqlalchemy.ext.hybrid import Comparator
class GrandparentTransformer(Comparator):
def operate(self, op, other):
def transform(q):
cls = self.__clause_element__()
parent_alias = aliased(cls)
return q.join(parent_alias, cls.parent).\
filter(op(parent_alias.parent, other))
return transform
Base = declarative_base()
class Node(Base):
__tablename__ = 'node'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('node.id'))
parent = relationship("Node", remote_side=id)
@hybrid_property
def grandparent(self):
return self.parent.parent
@grandparent.comparator
def grandparent(cls):
return GrandparentTransformer(cls)
The ``GrandparentTransformer`` overrides the core :meth:`.Operators.operate`
method at the base of the :class:`.Comparator` hierarchy to return a query-
transforming callable, which then runs the given comparison operation in a
particular context. Such as, in the example above, the ``operate`` method is
called, given the :attr:`.Operators.eq` callable as well as the right side of
the comparison ``Node(id=5)``. A function ``transform`` is then returned which
will transform a :class:`_query.Query` first to join to ``Node.parent``,
then to
compare ``parent_alias`` using :attr:`.Operators.eq` against the left and right
sides, passing into :meth:`_query.Query.filter`:
.. sourcecode:: pycon+sql
>>> from sqlalchemy.orm import Session
>>> session = Session()
{sql}>>> session.query(Node).\
... with_transformation(Node.grandparent==Node(id=5)).\
... all()
SELECT node.id AS node_id, node.parent_id AS node_parent_id
FROM node JOIN node AS node_1 ON node_1.id = node.parent_id
WHERE :param_1 = node_1.parent_id
{stop}
We can modify the pattern to be more verbose but flexible by separating the
"join" step from the "filter" step. The tricky part here is ensuring that
successive instances of ``GrandparentTransformer`` use the same
:class:`.AliasedClass` object against ``Node``. Below we use a simple
memoizing approach that associates a ``GrandparentTransformer`` with each
class::
class Node(Base):
# ...
@grandparent.comparator
def grandparent(cls):
# memoize a GrandparentTransformer
# per class
if '_gp' not in cls.__dict__:
cls._gp = GrandparentTransformer(cls)
return cls._gp
class GrandparentTransformer(Comparator):
def __init__(self, cls):
self.parent_alias = aliased(cls)
@property
def join(self):
def go(q):
return q.join(self.parent_alias, Node.parent)
return go
def operate(self, op, other):
return op(self.parent_alias.parent, other)
.. sourcecode:: pycon+sql
{sql}>>> session.query(Node).\
... with_transformation(Node.grandparent.join).\
... filter(Node.grandparent==Node(id=5))
SELECT node.id AS node_id, node.parent_id AS node_parent_id
FROM node JOIN node AS node_1 ON node_1.id = node.parent_id
WHERE :param_1 = node_1.parent_id
{stop}
The "transformer" pattern is an experimental pattern that starts to make usage
of some functional programming paradigms. While it's only recommended for
advanced and/or patient developers, there's probably a whole lot of amazing
things it can be used for.
""" # noqa
from .. import util
from ..orm import attributes
from ..orm import interfaces
HYBRID_METHOD = util.symbol("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 = util.symbol("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 hybrid_method(interfaces.InspectionAttrInfo):
"""A decorator which allows definition of a Python object method with both
instance-level and class-level behavior.
"""
is_attribute = True
extension_type = HYBRID_METHOD
def __init__(self, func, expr=None):
"""Create a new :class:`.hybrid_method`.
Usage is typically via decorator::
from sqlalchemy.ext.hybrid import hybrid_method
class SomeClass(object):
@hybrid_method
def value(self, x, y):
return self._value + x + y
@value.expression
def value(self, x, y):
return func.some_function(self._value, x, y)
"""
self.func = func
self.expression(expr or func)
def __get__(self, instance, owner):
if instance is None:
return self.expr.__get__(owner, owner.__class__)
else:
return self.func.__get__(instance, owner)
def expression(self, expr):
"""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
class hybrid_property(interfaces.InspectionAttrInfo):
"""A decorator which allows definition of a Python descriptor with both
instance-level and class-level behavior.
"""
is_attribute = True
extension_type = HYBRID_PROPERTY
def __init__(
self,
fget,
fset=None,
fdel=None,
expr=None,
custom_comparator=None,
update_expr=None,
):
"""Create a new :class:`.hybrid_property`.
Usage is typically via decorator::
from sqlalchemy.ext.hybrid import hybrid_property
class SomeClass(object):
@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 = expr
self.custom_comparator = custom_comparator
self.update_expr = update_expr
util.update_wrapper(self, fget)
def __get__(self, instance, owner):
if instance is None:
return self._expr_comparator(owner)
else:
return self.fget(instance)
def __set__(self, instance, value):
if self.fset is None:
raise AttributeError("can't set attribute")
self.fset(instance, value)
def __delete__(self, instance):
if self.fdel is None:
raise AttributeError("can't delete attribute")
self.fdel(instance)
def _copy(self, **kw):
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):
"""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(object):
# ...
@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
def getter(self, fget):
"""Provide a modifying decorator that defines a getter method.
.. versionadded:: 1.2
"""
return self._copy(fget=fget)
def setter(self, fset):
"""Provide a modifying decorator that defines a setter method."""
return self._copy(fset=fset)
def deleter(self, fdel):
"""Provide a modifying decorator that defines a deletion method."""
return self._copy(fdel=fdel)
def expression(self, expr):
"""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):
"""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):
"""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):
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(self.fget)
def _get_expr(self, expr):
def _expr(cls):
return ExprComparator(cls, expr(cls), self)
util.update_wrapper(_expr, expr)
return self._get_comparator(_expr)
def _get_comparator(self, comparator):
proxy_attr = attributes.create_proxied_attribute(self)
def expr_comparator(owner):
return proxy_attr(
owner,
self.__name__,
self,
comparator(owner),
doc=comparator.__doc__ or self.__doc__,
)
return expr_comparator
class Comparator(interfaces.PropComparator):
"""A helper class that allows easy construction of custom
:class:`~.orm.interfaces.PropComparator`
classes for usage with hybrids."""
property = None
def __init__(self, expression):
self.expression = expression
def __clause_element__(self):
expr = self.expression
if hasattr(expr, "__clause_element__"):
expr = expr.__clause_element__()
return expr
def adapt_to_entity(self, adapt_to_entity):
# interesting....
return self
class ExprComparator(Comparator):
def __init__(self, cls, expression, hybrid):
self.cls = cls
self.expression = expression
self.hybrid = hybrid
def __getattr__(self, key):
return getattr(self.expression, key)
@property
def info(self):
return self.hybrid.info
def _bulk_update_tuples(self, value):
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)]
@property
def property(self):
return self.expression.property
def operate(self, op, *other, **kwargs):
return op(self.expression, *other, **kwargs)
def reverse_operate(self, op, other, **kwargs):
return op(other, self.expression, **kwargs)
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