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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