mirror of
https://github.com/moparisthebest/SickRage
synced 2024-12-15 04:22:17 -05:00
637 lines
22 KiB
Python
637 lines
22 KiB
Python
# ext/mutable.py
|
|
# Copyright (C) 2005-2014 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
|
|
|
|
"""Provide support for tracking of in-place changes to scalar values,
|
|
which are propagated into ORM change events on owning parent objects.
|
|
|
|
.. versionadded:: 0.7 :mod:`sqlalchemy.ext.mutable` replaces SQLAlchemy's
|
|
legacy approach to in-place mutations of scalar values; see
|
|
:ref:`07_migration_mutation_extension`.
|
|
|
|
.. _mutable_scalars:
|
|
|
|
Establishing Mutability on Scalar Column Values
|
|
===============================================
|
|
|
|
A typical example of a "mutable" structure is a Python dictionary.
|
|
Following the example introduced in :ref:`types_toplevel`, we
|
|
begin with a custom type that marshals Python dictionaries into
|
|
JSON strings before being persisted::
|
|
|
|
from sqlalchemy.types import TypeDecorator, VARCHAR
|
|
import json
|
|
|
|
class JSONEncodedDict(TypeDecorator):
|
|
"Represents an immutable structure as a json-encoded string."
|
|
|
|
impl = VARCHAR
|
|
|
|
def process_bind_param(self, value, dialect):
|
|
if value is not None:
|
|
value = json.dumps(value)
|
|
return value
|
|
|
|
def process_result_value(self, value, dialect):
|
|
if value is not None:
|
|
value = json.loads(value)
|
|
return value
|
|
|
|
The usage of ``json`` is only for the purposes of example. The
|
|
:mod:`sqlalchemy.ext.mutable` extension can be used
|
|
with any type whose target Python type may be mutable, including
|
|
:class:`.PickleType`, :class:`.postgresql.ARRAY`, etc.
|
|
|
|
When using the :mod:`sqlalchemy.ext.mutable` extension, the value itself
|
|
tracks all parents which reference it. Below, we illustrate the a simple
|
|
version of the :class:`.MutableDict` dictionary object, which applies
|
|
the :class:`.Mutable` mixin to a plain Python dictionary::
|
|
|
|
from sqlalchemy.ext.mutable import Mutable
|
|
|
|
class MutableDict(Mutable, dict):
|
|
@classmethod
|
|
def coerce(cls, key, value):
|
|
"Convert plain dictionaries to MutableDict."
|
|
|
|
if not isinstance(value, MutableDict):
|
|
if isinstance(value, dict):
|
|
return MutableDict(value)
|
|
|
|
# this call will raise ValueError
|
|
return Mutable.coerce(key, value)
|
|
else:
|
|
return value
|
|
|
|
def __setitem__(self, key, value):
|
|
"Detect dictionary set events and emit change events."
|
|
|
|
dict.__setitem__(self, key, value)
|
|
self.changed()
|
|
|
|
def __delitem__(self, key):
|
|
"Detect dictionary del events and emit change events."
|
|
|
|
dict.__delitem__(self, key)
|
|
self.changed()
|
|
|
|
The above dictionary class takes the approach of subclassing the Python
|
|
built-in ``dict`` to produce a dict
|
|
subclass which routes all mutation events through ``__setitem__``. There are
|
|
variants on this approach, such as subclassing ``UserDict.UserDict`` or
|
|
``collections.MutableMapping``; the part that's important to this example is
|
|
that the :meth:`.Mutable.changed` method is called whenever an in-place
|
|
change to the datastructure takes place.
|
|
|
|
We also redefine the :meth:`.Mutable.coerce` method which will be used to
|
|
convert any values that are not instances of ``MutableDict``, such
|
|
as the plain dictionaries returned by the ``json`` module, into the
|
|
appropriate type. Defining this method is optional; we could just as well
|
|
created our ``JSONEncodedDict`` such that it always returns an instance
|
|
of ``MutableDict``, and additionally ensured that all calling code
|
|
uses ``MutableDict`` explicitly. When :meth:`.Mutable.coerce` is not
|
|
overridden, any values applied to a parent object which are not instances
|
|
of the mutable type will raise a ``ValueError``.
|
|
|
|
Our new ``MutableDict`` type offers a class method
|
|
:meth:`~.Mutable.as_mutable` which we can use within column metadata
|
|
to associate with types. This method grabs the given type object or
|
|
class and associates a listener that will detect all future mappings
|
|
of this type, applying event listening instrumentation to the mapped
|
|
attribute. Such as, with classical table metadata::
|
|
|
|
from sqlalchemy import Table, Column, Integer
|
|
|
|
my_data = Table('my_data', metadata,
|
|
Column('id', Integer, primary_key=True),
|
|
Column('data', MutableDict.as_mutable(JSONEncodedDict))
|
|
)
|
|
|
|
Above, :meth:`~.Mutable.as_mutable` returns an instance of ``JSONEncodedDict``
|
|
(if the type object was not an instance already), which will intercept any
|
|
attributes which are mapped against this type. Below we establish a simple
|
|
mapping against the ``my_data`` table::
|
|
|
|
from sqlalchemy import mapper
|
|
|
|
class MyDataClass(object):
|
|
pass
|
|
|
|
# associates mutation listeners with MyDataClass.data
|
|
mapper(MyDataClass, my_data)
|
|
|
|
The ``MyDataClass.data`` member will now be notified of in place changes
|
|
to its value.
|
|
|
|
There's no difference in usage when using declarative::
|
|
|
|
from sqlalchemy.ext.declarative import declarative_base
|
|
|
|
Base = declarative_base()
|
|
|
|
class MyDataClass(Base):
|
|
__tablename__ = 'my_data'
|
|
id = Column(Integer, primary_key=True)
|
|
data = Column(MutableDict.as_mutable(JSONEncodedDict))
|
|
|
|
Any in-place changes to the ``MyDataClass.data`` member
|
|
will flag the attribute as "dirty" on the parent object::
|
|
|
|
>>> from sqlalchemy.orm import Session
|
|
|
|
>>> sess = Session()
|
|
>>> m1 = MyDataClass(data={'value1':'foo'})
|
|
>>> sess.add(m1)
|
|
>>> sess.commit()
|
|
|
|
>>> m1.data['value1'] = 'bar'
|
|
>>> assert m1 in sess.dirty
|
|
True
|
|
|
|
The ``MutableDict`` can be associated with all future instances
|
|
of ``JSONEncodedDict`` in one step, using
|
|
:meth:`~.Mutable.associate_with`. This is similar to
|
|
:meth:`~.Mutable.as_mutable` except it will intercept all occurrences
|
|
of ``MutableDict`` in all mappings unconditionally, without
|
|
the need to declare it individually::
|
|
|
|
MutableDict.associate_with(JSONEncodedDict)
|
|
|
|
class MyDataClass(Base):
|
|
__tablename__ = 'my_data'
|
|
id = Column(Integer, primary_key=True)
|
|
data = Column(JSONEncodedDict)
|
|
|
|
|
|
Supporting Pickling
|
|
--------------------
|
|
|
|
The key to the :mod:`sqlalchemy.ext.mutable` extension relies upon the
|
|
placement of a ``weakref.WeakKeyDictionary`` upon the value object, which
|
|
stores a mapping of parent mapped objects keyed to the attribute name under
|
|
which they are associated with this value. ``WeakKeyDictionary`` objects are
|
|
not picklable, due to the fact that they contain weakrefs and function
|
|
callbacks. In our case, this is a good thing, since if this dictionary were
|
|
picklable, it could lead to an excessively large pickle size for our value
|
|
objects that are pickled by themselves outside of the context of the parent.
|
|
The developer responsibility here is only to provide a ``__getstate__`` method
|
|
that excludes the :meth:`~MutableBase._parents` collection from the pickle
|
|
stream::
|
|
|
|
class MyMutableType(Mutable):
|
|
def __getstate__(self):
|
|
d = self.__dict__.copy()
|
|
d.pop('_parents', None)
|
|
return d
|
|
|
|
With our dictionary example, we need to return the contents of the dict itself
|
|
(and also restore them on __setstate__)::
|
|
|
|
class MutableDict(Mutable, dict):
|
|
# ....
|
|
|
|
def __getstate__(self):
|
|
return dict(self)
|
|
|
|
def __setstate__(self, state):
|
|
self.update(state)
|
|
|
|
In the case that our mutable value object is pickled as it is attached to one
|
|
or more parent objects that are also part of the pickle, the :class:`.Mutable`
|
|
mixin will re-establish the :attr:`.Mutable._parents` collection on each value
|
|
object as the owning parents themselves are unpickled.
|
|
|
|
.. _mutable_composites:
|
|
|
|
Establishing Mutability on Composites
|
|
=====================================
|
|
|
|
Composites are a special ORM feature which allow a single scalar attribute to
|
|
be assigned an object value which represents information "composed" from one
|
|
or more columns from the underlying mapped table. The usual example is that of
|
|
a geometric "point", and is introduced in :ref:`mapper_composite`.
|
|
|
|
.. versionchanged:: 0.7
|
|
The internals of :func:`.orm.composite` have been
|
|
greatly simplified and in-place mutation detection is no longer enabled by
|
|
default; instead, the user-defined value must detect changes on its own and
|
|
propagate them to all owning parents. The :mod:`sqlalchemy.ext.mutable`
|
|
extension provides the helper class :class:`.MutableComposite`, which is a
|
|
slight variant on the :class:`.Mutable` class.
|
|
|
|
As is the case with :class:`.Mutable`, the user-defined composite class
|
|
subclasses :class:`.MutableComposite` as a mixin, and detects and delivers
|
|
change events to its parents via the :meth:`.MutableComposite.changed` method.
|
|
In the case of a composite class, the detection is usually via the usage of
|
|
Python descriptors (i.e. ``@property``), or alternatively via the special
|
|
Python method ``__setattr__()``. Below we expand upon the ``Point`` class
|
|
introduced in :ref:`mapper_composite` to subclass :class:`.MutableComposite`
|
|
and to also route attribute set events via ``__setattr__`` to the
|
|
:meth:`.MutableComposite.changed` method::
|
|
|
|
from sqlalchemy.ext.mutable import MutableComposite
|
|
|
|
class Point(MutableComposite):
|
|
def __init__(self, x, y):
|
|
self.x = x
|
|
self.y = y
|
|
|
|
def __setattr__(self, key, value):
|
|
"Intercept set events"
|
|
|
|
# set the attribute
|
|
object.__setattr__(self, key, value)
|
|
|
|
# alert all parents to the change
|
|
self.changed()
|
|
|
|
def __composite_values__(self):
|
|
return self.x, self.y
|
|
|
|
def __eq__(self, other):
|
|
return isinstance(other, Point) and \\
|
|
other.x == self.x and \\
|
|
other.y == self.y
|
|
|
|
def __ne__(self, other):
|
|
return not self.__eq__(other)
|
|
|
|
The :class:`.MutableComposite` class uses a Python metaclass to automatically
|
|
establish listeners for any usage of :func:`.orm.composite` that specifies our
|
|
``Point`` type. Below, when ``Point`` is mapped to the ``Vertex`` class,
|
|
listeners are established which will route change events from ``Point``
|
|
objects to each of the ``Vertex.start`` and ``Vertex.end`` attributes::
|
|
|
|
from sqlalchemy.orm import composite, mapper
|
|
from sqlalchemy import Table, Column
|
|
|
|
vertices = Table('vertices', metadata,
|
|
Column('id', Integer, primary_key=True),
|
|
Column('x1', Integer),
|
|
Column('y1', Integer),
|
|
Column('x2', Integer),
|
|
Column('y2', Integer),
|
|
)
|
|
|
|
class Vertex(object):
|
|
pass
|
|
|
|
mapper(Vertex, vertices, properties={
|
|
'start': composite(Point, vertices.c.x1, vertices.c.y1),
|
|
'end': composite(Point, vertices.c.x2, vertices.c.y2)
|
|
})
|
|
|
|
Any in-place changes to the ``Vertex.start`` or ``Vertex.end`` members
|
|
will flag the attribute as "dirty" on the parent object::
|
|
|
|
>>> from sqlalchemy.orm import Session
|
|
|
|
>>> sess = Session()
|
|
>>> v1 = Vertex(start=Point(3, 4), end=Point(12, 15))
|
|
>>> sess.add(v1)
|
|
>>> sess.commit()
|
|
|
|
>>> v1.end.x = 8
|
|
>>> assert v1 in sess.dirty
|
|
True
|
|
|
|
Coercing Mutable Composites
|
|
---------------------------
|
|
|
|
The :meth:`.MutableBase.coerce` method is also supported on composite types.
|
|
In the case of :class:`.MutableComposite`, the :meth:`.MutableBase.coerce`
|
|
method is only called for attribute set operations, not load operations.
|
|
Overriding the :meth:`.MutableBase.coerce` method is essentially equivalent
|
|
to using a :func:`.validates` validation routine for all attributes which
|
|
make use of the custom composite type::
|
|
|
|
class Point(MutableComposite):
|
|
# other Point methods
|
|
# ...
|
|
|
|
def coerce(cls, key, value):
|
|
if isinstance(value, tuple):
|
|
value = Point(*value)
|
|
elif not isinstance(value, Point):
|
|
raise ValueError("tuple or Point expected")
|
|
return value
|
|
|
|
.. versionadded:: 0.7.10,0.8.0b2
|
|
Support for the :meth:`.MutableBase.coerce` method in conjunction with
|
|
objects of type :class:`.MutableComposite`.
|
|
|
|
Supporting Pickling
|
|
--------------------
|
|
|
|
As is the case with :class:`.Mutable`, the :class:`.MutableComposite` helper
|
|
class uses a ``weakref.WeakKeyDictionary`` available via the
|
|
:meth:`MutableBase._parents` attribute which isn't picklable. If we need to
|
|
pickle instances of ``Point`` or its owning class ``Vertex``, we at least need
|
|
to define a ``__getstate__`` that doesn't include the ``_parents`` dictionary.
|
|
Below we define both a ``__getstate__`` and a ``__setstate__`` that package up
|
|
the minimal form of our ``Point`` class::
|
|
|
|
class Point(MutableComposite):
|
|
# ...
|
|
|
|
def __getstate__(self):
|
|
return self.x, self.y
|
|
|
|
def __setstate__(self, state):
|
|
self.x, self.y = state
|
|
|
|
As with :class:`.Mutable`, the :class:`.MutableComposite` augments the
|
|
pickling process of the parent's object-relational state so that the
|
|
:meth:`MutableBase._parents` collection is restored to all ``Point`` objects.
|
|
|
|
"""
|
|
from ..orm.attributes import flag_modified
|
|
from .. import event, types
|
|
from ..orm import mapper, object_mapper, Mapper
|
|
from ..util import memoized_property
|
|
import weakref
|
|
|
|
|
|
class MutableBase(object):
|
|
"""Common base class to :class:`.Mutable`
|
|
and :class:`.MutableComposite`.
|
|
|
|
"""
|
|
|
|
@memoized_property
|
|
def _parents(self):
|
|
"""Dictionary of parent object->attribute name on the parent.
|
|
|
|
This attribute is a so-called "memoized" property. It initializes
|
|
itself with a new ``weakref.WeakKeyDictionary`` the first time
|
|
it is accessed, returning the same object upon subsequent access.
|
|
|
|
"""
|
|
|
|
return weakref.WeakKeyDictionary()
|
|
|
|
@classmethod
|
|
def coerce(cls, key, value):
|
|
"""Given a value, coerce it into the target type.
|
|
|
|
Can be overridden by custom subclasses to coerce incoming
|
|
data into a particular type.
|
|
|
|
By default, raises ``ValueError``.
|
|
|
|
This method is called in different scenarios depending on if
|
|
the parent class is of type :class:`.Mutable` or of type
|
|
:class:`.MutableComposite`. In the case of the former, it is called
|
|
for both attribute-set operations as well as during ORM loading
|
|
operations. For the latter, it is only called during attribute-set
|
|
operations; the mechanics of the :func:`.composite` construct
|
|
handle coercion during load operations.
|
|
|
|
|
|
:param key: string name of the ORM-mapped attribute being set.
|
|
:param value: the incoming value.
|
|
:return: the method should return the coerced value, or raise
|
|
``ValueError`` if the coercion cannot be completed.
|
|
|
|
"""
|
|
if value is None:
|
|
return None
|
|
msg = "Attribute '%s' does not accept objects of type %s"
|
|
raise ValueError(msg % (key, type(value)))
|
|
|
|
@classmethod
|
|
def _listen_on_attribute(cls, attribute, coerce, parent_cls):
|
|
"""Establish this type as a mutation listener for the given
|
|
mapped descriptor.
|
|
|
|
"""
|
|
key = attribute.key
|
|
if parent_cls is not attribute.class_:
|
|
return
|
|
|
|
# rely on "propagate" here
|
|
parent_cls = attribute.class_
|
|
|
|
def load(state, *args):
|
|
"""Listen for objects loaded or refreshed.
|
|
|
|
Wrap the target data member's value with
|
|
``Mutable``.
|
|
|
|
"""
|
|
val = state.dict.get(key, None)
|
|
if val is not None:
|
|
if coerce:
|
|
val = cls.coerce(key, val)
|
|
state.dict[key] = val
|
|
val._parents[state.obj()] = key
|
|
|
|
def set(target, value, oldvalue, initiator):
|
|
"""Listen for set/replace events on the target
|
|
data member.
|
|
|
|
Establish a weak reference to the parent object
|
|
on the incoming value, remove it for the one
|
|
outgoing.
|
|
|
|
"""
|
|
if value is oldvalue:
|
|
return value
|
|
|
|
if not isinstance(value, cls):
|
|
value = cls.coerce(key, value)
|
|
if value is not None:
|
|
value._parents[target.obj()] = key
|
|
if isinstance(oldvalue, cls):
|
|
oldvalue._parents.pop(target.obj(), None)
|
|
return value
|
|
|
|
def pickle(state, state_dict):
|
|
val = state.dict.get(key, None)
|
|
if val is not None:
|
|
if 'ext.mutable.values' not in state_dict:
|
|
state_dict['ext.mutable.values'] = []
|
|
state_dict['ext.mutable.values'].append(val)
|
|
|
|
def unpickle(state, state_dict):
|
|
if 'ext.mutable.values' in state_dict:
|
|
for val in state_dict['ext.mutable.values']:
|
|
val._parents[state.obj()] = key
|
|
|
|
event.listen(parent_cls, 'load', load,
|
|
raw=True, propagate=True)
|
|
event.listen(parent_cls, 'refresh', load,
|
|
raw=True, propagate=True)
|
|
event.listen(attribute, 'set', set,
|
|
raw=True, retval=True, propagate=True)
|
|
event.listen(parent_cls, 'pickle', pickle,
|
|
raw=True, propagate=True)
|
|
event.listen(parent_cls, 'unpickle', unpickle,
|
|
raw=True, propagate=True)
|
|
|
|
|
|
class Mutable(MutableBase):
|
|
"""Mixin that defines transparent propagation of change
|
|
events to a parent object.
|
|
|
|
See the example in :ref:`mutable_scalars` for usage information.
|
|
|
|
"""
|
|
|
|
def changed(self):
|
|
"""Subclasses should call this method whenever change events occur."""
|
|
|
|
for parent, key in self._parents.items():
|
|
flag_modified(parent, key)
|
|
|
|
@classmethod
|
|
def associate_with_attribute(cls, attribute):
|
|
"""Establish this type as a mutation listener for the given
|
|
mapped descriptor.
|
|
|
|
"""
|
|
cls._listen_on_attribute(attribute, True, attribute.class_)
|
|
|
|
@classmethod
|
|
def associate_with(cls, sqltype):
|
|
"""Associate this wrapper with all future mapped columns
|
|
of the given type.
|
|
|
|
This is a convenience method that calls
|
|
``associate_with_attribute`` automatically.
|
|
|
|
.. warning::
|
|
|
|
The listeners established by this method are *global*
|
|
to all mappers, and are *not* garbage collected. Only use
|
|
:meth:`.associate_with` for types that are permanent to an
|
|
application, not with ad-hoc types else this will cause unbounded
|
|
growth in memory usage.
|
|
|
|
"""
|
|
|
|
def listen_for_type(mapper, class_):
|
|
for prop in mapper.column_attrs:
|
|
if isinstance(prop.columns[0].type, sqltype):
|
|
cls.associate_with_attribute(getattr(class_, prop.key))
|
|
|
|
event.listen(mapper, 'mapper_configured', listen_for_type)
|
|
|
|
@classmethod
|
|
def as_mutable(cls, sqltype):
|
|
"""Associate a SQL type with this mutable Python type.
|
|
|
|
This establishes listeners that will detect ORM mappings against
|
|
the given type, adding mutation event trackers to those mappings.
|
|
|
|
The type is returned, unconditionally as an instance, so that
|
|
:meth:`.as_mutable` can be used inline::
|
|
|
|
Table('mytable', metadata,
|
|
Column('id', Integer, primary_key=True),
|
|
Column('data', MyMutableType.as_mutable(PickleType))
|
|
)
|
|
|
|
Note that the returned type is always an instance, even if a class
|
|
is given, and that only columns which are declared specifically with
|
|
that type instance receive additional instrumentation.
|
|
|
|
To associate a particular mutable type with all occurrences of a
|
|
particular type, use the :meth:`.Mutable.associate_with` classmethod
|
|
of the particular :class:`.Mutable` subclass to establish a global
|
|
association.
|
|
|
|
.. warning::
|
|
|
|
The listeners established by this method are *global*
|
|
to all mappers, and are *not* garbage collected. Only use
|
|
:meth:`.as_mutable` for types that are permanent to an application,
|
|
not with ad-hoc types else this will cause unbounded growth
|
|
in memory usage.
|
|
|
|
"""
|
|
sqltype = types.to_instance(sqltype)
|
|
|
|
def listen_for_type(mapper, class_):
|
|
for prop in mapper.column_attrs:
|
|
if prop.columns[0].type is sqltype:
|
|
cls.associate_with_attribute(getattr(class_, prop.key))
|
|
|
|
event.listen(mapper, 'mapper_configured', listen_for_type)
|
|
|
|
return sqltype
|
|
|
|
|
|
|
|
class MutableComposite(MutableBase):
|
|
"""Mixin that defines transparent propagation of change
|
|
events on a SQLAlchemy "composite" object to its
|
|
owning parent or parents.
|
|
|
|
See the example in :ref:`mutable_composites` for usage information.
|
|
|
|
"""
|
|
|
|
def changed(self):
|
|
"""Subclasses should call this method whenever change events occur."""
|
|
|
|
for parent, key in self._parents.items():
|
|
|
|
prop = object_mapper(parent).get_property(key)
|
|
for value, attr_name in zip(
|
|
self.__composite_values__(),
|
|
prop._attribute_keys):
|
|
setattr(parent, attr_name, value)
|
|
|
|
def _setup_composite_listener():
|
|
def _listen_for_type(mapper, class_):
|
|
for prop in mapper.iterate_properties:
|
|
if (hasattr(prop, 'composite_class') and
|
|
isinstance(prop.composite_class, type) and
|
|
issubclass(prop.composite_class, MutableComposite)):
|
|
prop.composite_class._listen_on_attribute(
|
|
getattr(class_, prop.key), False, class_)
|
|
if not event.contains(Mapper, "mapper_configured", _listen_for_type):
|
|
event.listen(Mapper, 'mapper_configured', _listen_for_type)
|
|
_setup_composite_listener()
|
|
|
|
|
|
class MutableDict(Mutable, dict):
|
|
"""A dictionary type that implements :class:`.Mutable`.
|
|
|
|
.. versionadded:: 0.8
|
|
|
|
"""
|
|
|
|
def __setitem__(self, key, value):
|
|
"""Detect dictionary set events and emit change events."""
|
|
dict.__setitem__(self, key, value)
|
|
self.changed()
|
|
|
|
def __delitem__(self, key):
|
|
"""Detect dictionary del events and emit change events."""
|
|
dict.__delitem__(self, key)
|
|
self.changed()
|
|
|
|
def clear(self):
|
|
dict.clear(self)
|
|
self.changed()
|
|
|
|
@classmethod
|
|
def coerce(cls, key, value):
|
|
"""Convert plain dictionary to MutableDict."""
|
|
if not isinstance(value, MutableDict):
|
|
if isinstance(value, dict):
|
|
return MutableDict(value)
|
|
return Mutable.coerce(key, value)
|
|
else:
|
|
return value
|
|
|
|
def __getstate__(self):
|
|
return dict(self)
|
|
|
|
def __setstate__(self, state):
|
|
self.update(state)
|