[Zope] WebDAV Metadata

[HolgerSchmidt]

Wednesday, 2003-07-11 21:10 Dieter Maurer wrote:
DM> Holger Schmidt wrote at 2003-6-11 17:36 +0200:
DM>  > ...
DM>  > Using WebDAV you are able to attach Metadata to a document by calling
DM>  > PROPPATCH and you can get this Metadata by calling PROPFIND ...
DM>  > 
DM>  > Zope saves these Properties in the ZODB.
DM>  > 
DM>  > Properties are handled by OFS.PropertyManager.PropertyManager and for
DM>  > the Presentation OFS.PropertySheets.PropertySheet is used ...
DM>  > ---
DM>  > 
DM>  > I think it should be possible to "redirect" this Metadata, so a
DM>  > PROPPATCH would save the Metadata to 'MY' MySQL-DB and a PROPFIND
DM>  > would get it from 'MY' MySQL-DB ...
DM>  > 
DM>  > Has anybody ever done something like this before?

DM> I did something like this but for general attributes
DM> (not WebDAV properties).

DM> A word of warning:

DM>    You get lots of nasty problems when you distribute attribute
DM>    storage between ZODB and something external.
   
DM>    Moving and copying must be treated carefully.
DM>    Export/Import is likely to break.
DM>    Undo and Versions will bring your system in an inconsistent state.

DM> Apart from that, it is not too difficult:

DM>    Attribute access can be handled by letting "__getattr__"
DM>    fetch the attributes from the database on demand.

hmm ... this works as far as I do not change any attributes via WebDAV
or the "Zope Management Interface" ...
If I change these attributes every later WebDAV-Request returns the
values i changed the attributes to even if i return some other value in
my __getattr__-Method:

def __getattr__(self, name):
    # if one of my attributes return "MyValue :)"
    if (name[:5]=='LIRA_':
       return "MyValue :)"

    # none of my attributes => use __getattr__ of PropertyManager
    return PropertyManager.__getattr__(self, name)
# def __getattr__

is only __getattr__ called when webdav returns properties or are there
even some more functions that are touched by this operation?

DM>    For modification, the "PropertyManager" methods can
DM>    be overridden to update the values in the database
DM>    (be careful, if you delay update until transaction
DM>    commit (for efficiency). It may be too late then to
DM>    register the DA.).

Holger