Automatic migration for Archetypes schema changes

Hi all--

I have just checked in some semi-experimental auto-migration code for
Archetypes.  Reinstall Archetypes and go to the archetype_tool.  Click on
the Update Schema tab.  You will see all your types listed.  If you click
update, an automatic migration script will run and update the schema on all
of your objects to the current schema.  After that, the archetypes tool will
notice whenever your class schema change, and you can run the update as
needed on the changed classes.  The migration script is kind of dumb (see
below for details), so BE CAREFUL if you use this.  It works fine for me,
but YMMV.

Running the unit tests for the automigration will require an additional
product called ArchetypesTestUpdateSchema, which I am checking into the
Collective.

Enjoy

Geoff


    * ArchetypeTool.py: added mechanism for monitoring object schemae.
Schema
    are signed at registration time, and when a schema signature changes, it
is
    flagged in ArchetypeTool._types.  Added a new tab on the tool that lets
you
    see which types have schema that have changed and lets you update all
the
    schema in place.  You will need to reinstall Archetypes to make this
work.

    * Schema.py: Added toString and signature methods for use with update
    detection.  The toString method could use some improving.  Also made a
minor
    fix for the case of validating objects in place.

    * Field.py: Added toString and signature methods for use with update
    detection.  The toString method could use some improving.

    * BaseObject.py: Added an automigration method for handling updated
schema.
    The migration method works fine as long as calling a mutator on the
value
    returned by an object's accessor leaves the object unchanged.  If you
have
    objects for which this simple migration mechanism won't work, you will
need
    to override BaseObject._updateSchema.

    * tests/test_update_schema.py: A new test to make sure all the schema
updates
    work.  The individual subtests all work when run individually, but
something
    evil in Archetypes is causing POSKeyErrors to be raised when the suite
is
    run.  You will need to download the test product
ArchetypesTestUpdateSchema
    for this test to run.





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