[sync] Deleting attributes on the client

[Jan Schneider]

Zitat von Jan Schneider <jan at horde.org>:

> Zitat von Gunnar Wrobel <p at rdus.de>:
>
>> Hi!
>>
>> I'm currently testing SyncML support with Horde CVS HEAD based on a
>> Kolab backend (IMAP based data storage). The SyncML part is based on
>> SQL though. Clients are a Blackberry and a Nokia 6120c.
>>
>> In general both work fine wich is nice :) But I'm unable to delete
>> attributes on either of the clients (e.g. removing an e-mail address
>> or a phone number in an already synchronized addressbook entry on the
>> client). The data remains present on the server after removing the
>> attribute and synchronizing.
>>
>> This seems to come down to a problem with data exchange via
>> vCard/iCalendar. I'm not certain how things are supposed to work.
>>
>> Both clients will send vCard/iCalendar data wich contains only
>> attributes that actually have a value on the client. So if I delete an
>> attribute in a vCard it won't be mentioned in the update message from
>> the client.
>>
>> As te vCard has been exchanged between client and server before Turba
>> will fetch the old entry and overwrite any attributes provided by the
>> client on this addressbook entry.
>>
>> As I deleted the attribute the change will be missed by the server.
>>
>> Turba will delete an attribute if the attribute is provided with an
>> empty string as value. Is this the intended behaviour? Meaning that
>> the client update must indicate removal of an attribute by sending the
>> attribute with an empty value?
>>
>> As the clients don't do that I would need to use a client specific
>> converter but that would be fine. I'm just wondering whether that is
>> the intended mode of action. In fact using vCards/iCalendars as method
>> of data exchange seems somewhat limited in that context. But that
>> would be a SyncML limitation then.
>
> This is a very special problem limited to Turba. The problem is, that
> both could happen: we have attributes in Turba that are not supported
> by vCard or the sync client, or we have vCard attributes that are not
> supported by Turba.
>
> If we simply overwrite the contacts in Turba with the updated contact
> from the client, all special attributes from the Turba contact would
> disappear. This is obviously not what we want.
>
> I'm not sure how to deal with that. Maybe we could try to determine
> the vCard attributes that would have been supported by Turba and
> overwrite those unconditionally. But this seems fragile, since it
> would still delete attributes from Turba that are supported by vCard,
> but not by the client.

Actually this is not exactly true. IIRC some clients send a list of  
vCard/iCalendar attributes that they support. This could probably be  
used to build a complete list of attributes, with those set to empty  
that are missing.

Jan.

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