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Homogeneous values favoring maximum or minimum for ZODB conflict resolution

Project Description

Min/Max Value Conflict Resolution

This package provides support for homogeneous values favoring maximum or minimum for ZODB conflict resolution. See src/zope/minmax/minmax.txt for a detailed description.

Detailed Documentation

Conflict Resolution using Maximum or Minimum Values

The zope.minmax.AbstractValue class provides a super class which can be subclassed to store arbitrary homogeneous values in a persistent storage and apply different conflict resolution policies.

The subclasses defined here are resolving the conflicts using always either the maximum or the minimum of the conflicting values.

Maximum

The zope.minmax.Maximum class always resolves conflicts favoring the maximum value. Let’s instantiate one object and verify that it satisfies the interface.

>>> import zope.minmax
>>> import zope.interface.verify
>>> max_favored = zope.minmax.Maximum()
>>> zope.interface.verify.verifyObject(
...     zope.minmax.interfaces.IAbstractValue, max_favored)
True

We can confirm that the initial value is zero.

>>> bool(max_favored)
False
>>> print max_favored.value
None

Now, we can store a new value in the object.

>>> max_favored.value = 11
>>> print max_favored.value
11
>>> bool(max_favored)
True

Or we can use the methods.

>>> max_favored.__setstate__(4532)
>>> max_favored.__getstate__()
4532
>>> print max_favored.value
4532
>>> bool(max_favored)
True

Do notice that using a direct assignment to the value attribute is a more natural use.

Minimum

The zope.minmax.Minimum class always resolves conflicts favoring the minimum value. Again, we instantiate an object and verify that it satisfies the interface.

>>> min_favored = zope.minmax.Minimum()
>>> zope.interface.verify.verifyObject(
...     zope.minmax.interfaces.IAbstractValue, min_favored)
True

We need a confirmation that the initial value is zero.

>>> bool(min_favored)
False
>>> print min_favored.value
None

Let’s populate this one too.

>>> min_favored.value = 22
>>> print min_favored.value
22
>>> bool(min_favored)
True

Or we can use the methods, again.

>>> min_favored.__setstate__(8796)
>>> min_favored.__getstate__()
8796
>>> print min_favored.value
8796
>>> bool(min_favored)
True

Please, notice, again, that using a direct assignment to the value attribute is a more natural use.

Conflict Resolution

Now, we need to exercise the conflict resolution interface. First for the zope.minmax.Maximum:

Let’s try differing values larger than the old value.

>>> max_favored._p_resolveConflict(max_favored.value, 4536, 4535)
4536
>>> max_favored._p_resolveConflict(max_favored.value, 4573, 4574)
4574

What happens when all the values are equal, including the old.

>>> max_favored._p_resolveConflict(max_favored.value, 4532, 4532)
4532

Notice that when the old value is larger than both the committed and new, it is still disregarded.

>>> max_favored._p_resolveConflict(max_favored.value, 4531, 4530)
4531

Now, the zope.minmax.Minimum:

Let’s try differing values smaller than the old value.

>>> min_favored._p_resolveConflict(min_favored.value, 8792, 8791)
8791
>>> min_favored._p_resolveConflict(min_favored.value, 8785, 8786)
8785

What happens when all the values are equal, including the old.

>>> min_favored._p_resolveConflict(min_favored.value, 8796, 8796)
8796

Notice that when the old value is smaller than both the committed and new, it is still disregarded.

>>> min_favored._p_resolveConflict(min_favored.value, 8798, 8799)
8798

How about an example that is not numerical?

>>> max_word = zope.minmax.Maximum('joy')
>>> print max_word.value
joy
>>> bool(max_word)
True
>>> max_word._p_resolveConflict(max_word.value, 'happiness', 'exuberance')
'happiness'
>>> max_word._p_resolveConflict(max_word.value, 'exuberance', 'happiness')
'happiness'
>>> min_word = zope.minmax.Minimum(max_word.value)
>>> print min_word.value
joy
>>> bool(min_word)
True
>>> min_word._p_resolveConflict(min_word.value, 'happiness', 'exuberance')
'exuberance'
>>> min_word._p_resolveConflict(min_word.value, 'exuberance', 'happiness')
'exuberance'

As indicated, we don’t need to have numbers, just homegeneous items. The homogeneous values are not really inherently required. However, it makes no sense to apply min() or max() on, say, one number and one string. Simply, the ordering relations do not work at all on heterogeneous values.

CHANGES

1.1.2 (2009-09-24)

  • Use the standard Python doctest module instead of the deprecated zope.testing.doctest.

1.1.1 (2009-09-09)

  • Fixed homepage link and mailing list address.
  • Cleaned up.

1.1 (2007-10-02)

  • Refactored package setup.

1.0 (2007-09-28)

  • No further changes since 1.0b2

1.0b2 (2007-07-09)

  • Removed _p_independent method from AbstractValue class.

1.0b1 (2007-07-03)

  • Initial release.

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