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src/persistent/README.txt
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Persistence support
===================
(This document is under construction. More basic documentation will
eventually appear here.)
(This document is under construction. More basic documentation will eventually
appear here.)
Overriding __getattr__, __getattribute__, __setattr__, and __delattr__
-----------------------------------------------------------------------
Overriding `__getattr__`, `__getattribute__`, `__setattr__`, and `__delattr__`
------------------------------------------------------------------------------
Subclasses can override the attribute-management methods. For the
__getattr__ method, the behavior is like that for regular Python
`__getattr__` method, the behavior is like that for regular Python
classes and for earlier versions of ZODB 3.
For __getattribute__, __setattr__, and __delattr__, it is necessary to
call certain methods defined by persistent.Persistent. Detailed
For `__getattribute__`, __setattr__`, and `__delattr__`, it is necessary
to call certain methods defined by `persistent.Persistent`. Detailed
examples and documentation is provided in the test module,
persistent.tests.test_overriding_attrs.
`persistent.tests.test_overriding_attrs`.
src/persistent/tests/persistent.txt
View file @ c732b082
Tests for persistent.Persistent
===============================
Tests for `persistent.Persistent`
=================================
This document is an extended doc test that covers the basics of the
Persistent base class. The test expects a class named 'P' to be
provided in its globals. The P class implements the Persistent
Persistent base class. The test expects a class named `P` to be
provided in its globals. The `P` class implements the `Persistent`
interface.
Test framework
--------------
The class P needs to behave like ExampleP. (Note that the code below
The class `P` needs to behave like `ExampleP`. (Note that the code below
is *not* part of the tests.)
class ExampleP(Persistent):
def __init__(self):
self.x = 0
def inc(self):
self.x += 1
::
class ExampleP(Persistent):
def __init__(self):
self.x = 0
def inc(self):
self.x += 1
The tests use stub data managers. A data manager is responsible for
loading and storing the state of a persistent object. It's stored in
the _p_jar attribute of a persistent object.
the ``_p_jar`` attribute of a persistent object.
>>> class DM:
... def __init__(self):
... self.called = 0
... def register(self, ob):
... self.called += 1
... def setstate(self, ob):
... ob.__setstate__({'x': 42})
>>> class DM:
... def __init__(self):
... self.called = 0
... def register(self, ob):
... self.called += 1
... def setstate(self, ob):
... ob.__setstate__({'x': 42})
>>> class BrokenDM(DM):
... def register(self,ob):
... self.called += 1
... raise NotImplementedError
... def setstate(self,ob):
... raise NotImplementedError
>>> class BrokenDM(DM):
... def register(self,ob):
... self.called += 1
... raise NotImplementedError
... def setstate(self,ob):
... raise NotImplementedError
>>> from persistent import Persistent
>>> from persistent import Persistent
Test Persistent without Data Manager
------------------------------------
First do some simple tests of a Persistent instance that does not have
a data manager (_p_jar).
>>> p = P()
>>> p.x
0
>>> p._p_changed
False
>>> p._p_state
0
>>> p._p_jar
>>> p._p_oid
Verify that modifications have no effect on _p_state of _p_changed.
>>> p.inc()
>>> p.inc()
>>> p.x
2
>>> p._p_changed
False
>>> p._p_state
0
a data manager (``_p_jar``).
>>> p = P()
>>> p.x
0
>>> p._p_changed
False
>>> p._p_state
0
>>> p._p_jar
>>> p._p_oid
Verify that modifications have no effect on ``_p_state`` of ``_p_changed``.
>>> p.inc()
>>> p.inc()
>>> p.x
2
>>> p._p_changed
False
>>> p._p_state
0
Try all sorts of different ways to change the object's state.
>>> p._p_deactivate()
>>> p._p_state
0
>>> p._p_changed = True
>>> p._p_state
0
>>> del p._p_changed
>>> p._p_changed
False
>>> p._p_state
0
>>> p.x
2
>>> p._p_deactivate()
>>> p._p_state
0
>>> p._p_changed = True
>>> p._p_state
0
>>> del p._p_changed
>>> p._p_changed
False
>>> p._p_state
0
>>> p.x
2
Test Persistent with Data Manager
---------------------------------
Next try some tests of an object with a data manager. The DM class is
Next try some tests of an object with a data manager. The `DM` class is
a simple testing stub.
>>> p = P()
>>> dm = DM()
>>> p._p_oid = "00000012"
>>> p._p_jar = dm
>>> p._p_changed
0
>>> dm.called
0
Modifying the object marks it as changed and registers it with the
data manager. Subsequent modifications don't have additional
side-effects.
>>> p.inc()
>>> p._p_changed
1
>>> dm.called
1
>>> p.inc()
>>> p._p_changed
1
>>> dm.called
1
>>> p = P()
>>> dm = DM()
>>> p._p_oid = "00000012"
>>> p._p_jar = dm
>>> p._p_changed
0
>>> dm.called
0
Modifying the object marks it as changed and registers it with the data
manager. Subsequent modifications don't have additional side-effects.
>>> p.inc()
>>> p._p_changed
1
>>> dm.called
1
>>> p.inc()
>>> p._p_changed
1
>>> dm.called
1
It's not possible to deactivate a modified object.
>>> p._p_deactivate()
>>> p._p_changed
1
It is possible to invalidate it. That's the key difference
between deactivation and invalidation.
>>> p._p_invalidate()
>>> p._p_state
-1
Now that the object is a ghost, any attempt to modify it will
require that it be unghosted first. The test data manager
has the odd property that it sets the object's 'x' attribute
to 42 when it is unghosted.
>>> p.inc()
>>> p.x
43
>>> dm.called
2
You can manually reset the changed field to False, although
it's not clear why you would want to do that. The object
changes to the UPTODATE state but retains its modifications.
>>> p._p_changed = False
>>> p._p_state
0
>>> p._p_changed
False
>>> p.x
43
>>> p.inc()
>>> p._p_changed
True
>>> dm.called
3
__getstate__() and __setstate__()
---------------------------------
The next several tests cover the __getstate__() and __setstate__()
>>> p._p_deactivate()
>>> p._p_changed
1
It is possible to invalidate it. That's the key difference between
deactivation and invalidation.
>>> p._p_invalidate()
>>> p._p_state
-1
Now that the object is a ghost, any attempt to modify it will require that it
be unghosted first. The test data manager has the odd property that it sets
the object's ``x`` attribute to ``42`` when it is unghosted.
>>> p.inc()
>>> p.x
43
>>> dm.called
2
You can manually reset the changed field to ``False``, although it's not clear
why you would want to do that. The object changes to the ``UPTODATE`` state
but retains its modifications.
>>> p._p_changed = False
>>> p._p_state
0
>>> p._p_changed
False
>>> p.x
43
>>> p.inc()
>>> p._p_changed
True
>>> dm.called
3
``__getstate__()`` and ``__setstate__()``
-----------------------------------------
The next several tests cover the ``__getstate__()`` and ``__setstate__()``
implementations.
>>> p = P()
>>> state = p.__getstate__()
>>> isinstance(state, dict)
True
>>> state['x']
0
>>> p._p_state
0
>>> p = P()
>>> state = p.__getstate__()
>>> isinstance(state, dict)
True
>>> state['x']
0
>>> p._p_state
0
Calling setstate always leaves the object in the uptodate state?
(I'm not entirely clear on this one.)
>>> p.__setstate__({'x': 5})
>>> p._p_state
0
>>> p.__setstate__({'x': 5})
>>> p._p_state
0
Assigning to a volatile attribute has no effect on the object state.
>>> p._v_foo = 2
>>> p.__getstate__()
{'x': 5}
>>> p._p_state
0
>>> p._v_foo = 2
>>> p.__getstate__()
{'x': 5}
>>> p._p_state
0
The _p_serial attribute is not affected by calling setstate.
The ``_p_serial`` attribute is not affected by calling setstate.
>>> p._p_serial = "00000012"
>>> p.__setstate__(p.__getstate__())
>>> p._p_serial
'00000012'
>>> p._p_serial = "00000012"
>>> p.__setstate__(p.__getstate__())
>>> p._p_serial
'00000012'
Change Ghost test
-----------------
If an object is a ghost and its _p_changed is set to True (any true value),
it should activate (unghostify) the object. This behavior is new in ZODB
3.6; before then, an attempt to do "ghost._p_changed = True" was ignored.
>>> p = P()
>>> p._p_jar = DM()
>>> p._p_oid = 1
>>> p._p_deactivate()
>>> p._p_changed # None
>>> p._p_state # ghost state
-1
>>> p._p_changed = True
>>> p._p_changed
1
>>> p._p_state # changed state
1
>>> p.x
42
If an object is a ghost and its ``_p_changed`` is set to ``True`` (any true
value), it should activate (unghostify) the object. This behavior is new in
ZODB 3.6; before then, an attempt to do ``ghost._p_changed = True`` was
ignored.
>>> p = P()
>>> p._p_jar = DM()
>>> p._p_oid = 1
>>> p._p_deactivate()
>>> p._p_changed # None
>>> p._p_state # ghost state
-1
>>> p._p_changed = True
>>> p._p_changed
1
>>> p._p_state # changed state
1
>>> p.x
42
Activate, deactivate, and invalidate
------------------------------------
Some of these tests are redundant, but are included to make sure there
are explicit and simple tests of _p_activate(), _p_deactivate(), and
_p_invalidate().
>>> p = P()
>>> p._p_oid = 1
>>> p._p_jar = DM()
>>> p._p_deactivate()
>>> p._p_state
-1
>>> p._p_activate()
>>> p._p_state
0
>>> p.x
42
>>> p.inc()
>>> p.x
43
>>> p._p_state
1
>>> p._p_invalidate()
>>> p._p_state
-1
>>> p.x
42
are explicit and simple tests of ``_p_activate()``, ``_p_deactivate()``, and
``_p_invalidate()``.
>>> p = P()
>>> p._p_oid = 1
>>> p._p_jar = DM()
>>> p._p_deactivate()
>>> p._p_state
-1
>>> p._p_activate()
>>> p._p_state
0
>>> p.x
42
>>> p.inc()
>>> p.x
43
>>> p._p_state
1
>>> p._p_invalidate()
>>> p._p_state
-1
>>> p.x
42
Test failures
-------------
The following tests cover various errors cases.
When an object is modified, it registers with its data manager. If
that registration fails, the exception is propagated and the object
stays in the up-to-date state. It shouldn't change to the modified
state, because it won't be saved when the transaction commits.
>>> p = P()
>>> p._p_oid = 1
>>> p._p_jar = BrokenDM()
>>> p._p_state
0
>>> p._p_jar.called
0
>>> p._p_changed = 1
Traceback (most recent call last):
...
NotImplementedError
>>> p._p_jar.called
1
>>> p._p_state
0
Make sure that exceptions that occur inside the data manager's
setstate() method propagate out to the caller.
>>> p = P()
>>> p._p_oid = 1
>>> p._p_jar = BrokenDM()
>>> p._p_deactivate()
>>> p._p_state
-1
>>> p._p_activate()
Traceback (most recent call last):
...
NotImplementedError
>>> p._p_state
-1
Special test to cover layout of __dict__
----------------------------------------
We once had a bug in the Persistent class that calculated an incorrect
offset for the __dict__ attribute. It assigned __dict__ and _p_jar to
the same location in memory. This is a simple test to make sure they
have different locations.
>>> p = P()
>>> p.inc()
>>> p.inc()
>>> 'x' in p.__dict__
True
>>> p._p_jar
When an object is modified, it registers with its data manager. If that
registration fails, the exception is propagated and the object stays in the
up-to-date state. It shouldn't change to the modified state, because it won't
be saved when the transaction commits.
>>> p = P()
>>> p._p_oid = 1
>>> p._p_jar = BrokenDM()
>>> p._p_state
0
>>> p._p_jar.called
0
>>> p._p_changed = 1
Traceback (most recent call last):
...
NotImplementedError
>>> p._p_jar.called
1
>>> p._p_state
0
Make sure that exceptions that occur inside the data manager's ``setstate()``
method propagate out to the caller.
>>> p = P()
>>> p._p_oid = 1
>>> p._p_jar = BrokenDM()
>>> p._p_deactivate()
>>> p._p_state
-1
>>> p._p_activate()
Traceback (most recent call last):
...
NotImplementedError
>>> p._p_state
-1
Special test to cover layout of ``__dict__``
--------------------------------------------
We once had a bug in the `Persistent` class that calculated an incorrect
offset for the ``__dict__`` attribute. It assigned ``__dict__`` and
``_p_jar`` to the same location in memory. This is a simple test to make sure
they have different locations.
>>> p = P()
>>> p.inc()
>>> p.inc()
>>> 'x' in p.__dict__
True
>>> p._p_jar
Inheritance and metaclasses
---------------------------
Simple tests to make sure it's possible to inherit from the Persistent
base class multiple times. There used to be metaclasses involved in
Persistent that probably made this a more interesting test.
>>> class A(Persistent):
... pass
>>> class B(Persistent):
... pass
>>> class C(A, B):
... pass
>>> class D(object):
... pass
>>> class E(D, B):
... pass
>>> a = A()
>>> b = B()
>>> c = C()
>>> d = D()
>>> e = E()
Also make sure that it's possible to define Persistent classes that
have a custom metaclass.
>>> class alternateMeta(type):
... type
>>> class alternate(object):
... __metaclass__ = alternateMeta
>>> class mixedMeta(alternateMeta, type):
... pass
>>> class mixed(alternate, Persistent):
... pass
>>> class mixed(Persistent, alternate):
... pass
Simple tests to make sure it's possible to inherit from the `Persistent` base
class multiple times. There used to be metaclasses involved in `Persistent`
that probably made this a more interesting test.
>>> class A(Persistent):
... pass
>>> class B(Persistent):
... pass
>>> class C(A, B):
... pass
>>> class D(object):
... pass
>>> class E(D, B):
... pass
>>> a = A()
>>> b = B()
>>> c = C()
>>> d = D()
>>> e = E()
Also make sure that it's possible to define `Persistent` classes that have a
custom metaclass.
>>> class alternateMeta(type):
... type
>>> class alternate(object):
... __metaclass__ = alternateMeta
>>> class mixedMeta(alternateMeta, type):
... pass
>>> class mixed(alternate, Persistent):
... pass
>>> class mixed(Persistent, alternate):
... pass
Basic type structure
--------------------
>>> Persistent.__dictoffset__
0
>>> Persistent.__weakrefoffset__
0
>>> Persistent.__basicsize__ > object.__basicsize__
True
>>> P.__dictoffset__ > 0
True
>>> P.__weakrefoffset__ > 0
True
>>> P.__dictoffset__ < P.__weakrefoffset__
True
>>> P.__basicsize__ > Persistent.__basicsize__
True
>>> Persistent.__dictoffset__
0
>>> Persistent.__weakrefoffset__
0
>>> Persistent.__basicsize__ > object.__basicsize__
True
>>> P.__dictoffset__ > 0
True
>>> P.__weakrefoffset__ > 0
True
>>> P.__dictoffset__ < P.__weakrefoffset__
True
>>> P.__basicsize__ > Persistent.__basicsize__
True
Slots
-----
These are some simple tests of classes that have an __slots__
These are some simple tests of classes that have an ``__slots__``
attribute. Some of the classes should have slots, others shouldn't.
>>> class noDict(object):
... __slots__ = ['foo']
>>> class p_noDict(Persistent):
... __slots__ = ['foo']
>>> class p_shouldHaveDict(p_noDict):
... pass
>>> p_noDict.__dictoffset__
0
>>> x = p_noDict()
>>> x.foo = 1
>>> x.foo
1
>>> x.bar = 1
Traceback (most recent call last):
...
AttributeError: 'p_noDict' object has no attribute 'bar'
>>> x._v_bar = 1
Traceback (most recent call last):
...
AttributeError: 'p_noDict' object has no attribute '_v_bar'
>>> x.__dict__
Traceback (most recent call last):
...
AttributeError: 'p_noDict' object has no attribute '__dict__'
The various _p_ attributes are unaffected by slots.
>>> p._p_oid
>>> p._p_jar
>>> p._p_state
0
>>> class noDict(object):
... __slots__ = ['foo']
>>> class p_noDict(Persistent):
... __slots__ = ['foo']
>>> class p_shouldHaveDict(p_noDict):
... pass
>>> p_noDict.__dictoffset__
0
>>> x = p_noDict()
>>> x.foo = 1
>>> x.foo
1
>>> x.bar = 1
Traceback (most recent call last):
...
AttributeError: 'p_noDict' object has no attribute 'bar'
>>> x._v_bar = 1
Traceback (most recent call last):
...
AttributeError: 'p_noDict' object has no attribute '_v_bar'
>>> x.__dict__
Traceback (most recent call last):
...
AttributeError: 'p_noDict' object has no attribute '__dict__'
The various _p_ attributes are unaffected by slots.
>>> p._p_oid
>>> p._p_jar
>>> p._p_state
0
If the most-derived class does not specify
>>> p_shouldHaveDict.__dictoffset__ > 0
True
>>> x = p_shouldHaveDict()
>>> isinstance(x.__dict__, dict)
True
>>> p_shouldHaveDict.__dictoffset__ > 0
True
>>> x = p_shouldHaveDict()
>>> isinstance(x.__dict__, dict)
True
Pickling
--------
There's actually a substantial effort involved in making subclasses of
Persistent work with plain-old pickle. The ZODB serialization layer
never calls pickle on an object; it pickles the object's class
description and its state as two separate pickles.
>>> import pickle
>>> p = P()
>>> p.inc()
>>> p2 = pickle.loads(pickle.dumps(p))
>>> p2.__class__ is P
True
>>> p2.x == p.x
True
We should also test that pickle works with custom getstate and
setstate. Perhaps even reduce. The problem is that pickling depends
on finding the class in a particular module, and classes defined here
won't appear in any module. We could require each user of the tests
to define a base class, but that might be tedious.
`Persistent` work with plain-old pickle. The ZODB serialization layer never
calls pickle on an object; it pickles the object's class description and its
state as two separate pickles.
>>> import pickle
>>> p = P()
>>> p.inc()
>>> p2 = pickle.loads(pickle.dumps(p))
>>> p2.__class__ is P
True
>>> p2.x == p.x
True
We should also test that pickle works with custom getstate and setstate.
Perhaps even reduce. The problem is that pickling depends on finding the
class in a particular module, and classes defined here won't appear in any
module. We could require each user of the tests to define a base class, but
that might be tedious.
Interfaces
----------
Some versions of Zope and ZODB have the zope.interfaces package
available. If it is available, then persistent will be associated
with several interfaces. It's hard to write a doctest test that runs
the tests only if zope.interface is available, so this test looks a
little unusual. One problem is that the assert statements won't do
anything if you run with -O.
>>> try:
... import zope.interface
... except ImportError:
... pass
... else:
... from persistent.interfaces import IPersistent
... assert IPersistent.implementedBy(Persistent)
... p = Persistent()
... assert IPersistent.providedBy(p)
... assert IPersistent.implementedBy(P)
... p = P()
... assert IPersistent.providedBy(p)
Some versions of Zope and ZODB have the `zope.interfaces` package available.
If it is available, then persistent will be associated with several
interfaces. It's hard to write a doctest test that runs the tests only if
`zope.interface` is available, so this test looks a little unusual. One
problem is that the assert statements won't do anything if you run with `-O`.
>>> try:
... import zope.interface
... except ImportError:
... pass
... else:
... from persistent.interfaces import IPersistent
... assert IPersistent.implementedBy(Persistent)
... p = Persistent()
... assert IPersistent.providedBy(p)
... assert IPersistent.implementedBy(P)
... p = P()
... assert IPersistent.providedBy(p)
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