[Yanel-development] [yarep] fallback not working

[Michael Wechner]

Josias Thöny wrote:

>On Wed, 2006-11-15 at 23:29 +0100, Michael Wechner wrote:
>  
>
>>Josias Thöny wrote:
>>
>>    
>>
>>>Hi all,
>>>
>>>This is a yarep question. Sorry for posting to the yanel list. Is there
>>>a better place for yarep questions?
>>> 
>>>
>>>      
>>>
>>not yet ;-)
>>
>>    
>>
>>>The fallback mechanism of yarep allows to access files in the repository
>>>which are not registered in the uid/path map.
>>> 
>>>
>>>      
>>>
>>right
>>
>>    
>>
>>>If you want to read the content for a given path from yarep, and the
>>>path is not found in the uid/path map, it will assume that path=uid and
>>>read that path directly from the repository.
>>>
>>>There is a problem with this approach:
>>>- say there is a file /foo.txt in the repository, but it's not
>>>registered in the path-map.
>>>- someone reads the path "/foo.txt". it will work.
>>>- now someone writes to this path. since the map has no uid for this
>>>path, one will be created, say 1234, and the content will be written to
>>>the file /1234
>>>
>>>This means we now have two different files for the same path in the
>>>repository, which is bad.
>>>
>>>Furthermore, methods like getChildren() or delete() do not work if the
>>>path is not registered in the map.
>>>
>>>I therefore propose to remove the fallback, unless someone has an idea
>>>how to fix it.
>>> 
>>>
>>>      
>>>
>>I think we should fix it somehow and I hope we are able to ;-)
>>    
>>
>
>What about the following situation:
>
>Assume there is a path /abc.html which has the uid /a.html:
>path: /abc.html -> uid: /a.html
>
>Now someone wants to write to the path /a.html
>What should the repository do? 
>Currently it does the following:
>- Look up in the map 
>-> no uid exists for path /a.html 
>-> uid 1234 will be created 
>  
>

for reading this should not be the case, but I think for writing it is 
as you say

>-> content will be written to /1234
>  
>

right

>If you allow fallback in the write method, this will happen:
>-> no uid exists for path /a.html 
>-> check if file /a.html exists in the repo content -> yes!
>-> write to file /a.html
>
>Now we have overwritten the content of path /abc.html
>  
>

agreed, because people accessing abc will not like this

>I don't think the fallback can be fixed, because it's not clean.
>
>  
>
>>It also took me quite some time to introduce the fallback because
>>I also thought that it is "evil", but there is a lot of existing data
>>for which it would be nice use the Path/Map repo implementation, but at 
>>the same time one would have to create all map entries. Well, one could 
>>argue to write an import method
>>
>>    
>>
>>>It probably could be replaced by a special map implementation which
>>>directly maps paths to uids.
>>>
>>>      
>>>
>>such an implementation exist namely the VFileSystemImplementation, but it
>>had the disadvantage that "/" cannot be translated into for instance 
>>/index.html
>>    
>>
>
>Ok, let's use this implementation then. What does the V stand for?
>virtual?
>  
>

yes

>Actually if we want to have an implementation which directly maps the
>paths to the fs, I don't think it's the job of such an implementation to
>translate paths like you mentioned.
>  
>

I guess you are right

Let me think an hour ;-)

Michi

>josias
>
>  
>
>>>WDYT? 
>>> 
>>>
>>>      
>>>
>>I would suggest that we implement fallback also for the following cases:
>>
>>- add
>>- delete
>>- getChildren
>>- ...
>>
>>but yes, the question is if this is actually going to end ...
>>
>>WDYT?
>>
>>Michi
>>
>>    
>>
>>>Josias
>>>
>>>
>>>
>>>_______________________________________________
>>>Yanel-development mailing list
>>>Yanel-development at wyona.com
>>>http://wyona.com/cgi-bin/mailman/listinfo/yanel-development
>>>
>>> 
>>>
>>>      
>>>
>>    
>>
>
>
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>
>  
>


-- 
Michael Wechner
Wyona      -   Open Source Content Management   -    Apache Lenya
http://www.wyona.com                      http://lenya.apache.org
michael.wechner at wyona.com                        michi at apache.org
+41 44 272 91 61