mirror of
https://github.com/janeczku/calibre-web
synced 2024-12-11 10:40:32 +00:00
809 lines
27 KiB
Python
809 lines
27 KiB
Python
# ext/hybrid.py
|
|
# Copyright (C) 2005-2013 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
|
|
|
|
"""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
|
|
returns a new SQL expression::
|
|
|
|
>>> print Interval.length
|
|
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.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"
|
|
|
|
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 :attr:`.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
|
|
|
|
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
|
|
|
|
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. Two variants of 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.
|
|
|
|
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 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`
|
|
object and return a new one. The :class:`.Query` object includes a
|
|
method :meth:`.with_transformation` that returns a new :class:`.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` where we :meth:`~.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` 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`
|
|
first to join to ``Node.parent``, then to compare ``parent_alias``
|
|
using :attr:`.Operators.eq` against the left and right sides, passing
|
|
into :class:`.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.
|
|
|
|
"""
|
|
from .. import util
|
|
from ..orm import attributes, 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`
|
|
attibute.
|
|
|
|
.. seealso::
|
|
|
|
:attr:`.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`
|
|
attibute.
|
|
|
|
.. seealso::
|
|
|
|
:attr:`.Mapper.all_orm_attributes`
|
|
|
|
"""
|
|
|
|
class hybrid_method(interfaces._InspectionAttr):
|
|
"""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.expr = 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
|
|
return self
|
|
|
|
|
|
class hybrid_property(interfaces._InspectionAttr):
|
|
"""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):
|
|
"""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 or fget
|
|
util.update_wrapper(self, fget)
|
|
|
|
def __get__(self, instance, owner):
|
|
if instance is None:
|
|
return self.expr(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 setter(self, fset):
|
|
"""Provide a modifying decorator that defines a value-setter method."""
|
|
|
|
self.fset = fset
|
|
return self
|
|
|
|
def deleter(self, fdel):
|
|
"""Provide a modifying decorator that defines a
|
|
value-deletion method."""
|
|
|
|
self.fdel = fdel
|
|
return self
|
|
|
|
def expression(self, expr):
|
|
"""Provide a modifying decorator that defines a SQL-expression
|
|
producing method."""
|
|
|
|
self.expr = expr
|
|
return self
|
|
|
|
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`.
|
|
|
|
"""
|
|
|
|
proxy_attr = attributes.\
|
|
create_proxied_attribute(self)
|
|
|
|
def expr(owner):
|
|
return proxy_attr(owner, self.__name__, self, comparator(owner))
|
|
self.expr = expr
|
|
return self
|
|
|
|
|
|
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
|
|
while hasattr(expr, '__clause_element__'):
|
|
expr = expr.__clause_element__()
|
|
return expr
|
|
|
|
def adapted(self, adapter):
|
|
# interesting....
|
|
return self
|