[Digikam-devel] Update query fails

[Marcel Wiesweg]

Have a look at the (rather complex) CollectionScanner.

The problem is the nature of our scan, which will always run in all kinds of 
race conditions with the file system.

When a folder is moved, we may notice that it is removed at the previous 
location. Later, we see it appear at the new location. It would be unfortunate 
to have completely deleted all album metadata in the meantime. Therefore, it 
is made a stale album, which can be resurrected later if a new place can be 
identified.

This is done in a similar way for images. Here, we can identify them by 
content, so the storage of "removed" images is even more extensively done.



> This query is executed in core/libs/database/coredb.cpp:576 in the function
> to create stale Albums, that is why the albumRoot has been set to 0.
> 
> I would like to ask why is there a need to create the stale Albums?
> 
> Regards
> ᐧ
> 
> On Wed, Jun 1, 2016 at 1:19 AM, Marcel Wiesweg <marcel.wiesweg at gmx.de>
> 
> wrote:
> > Please check the context where it is called, but I am quite sure that
> > there is
> > a special meaning in setting album root to 0.
> > I'm sure there is a similar case with deleted images where album is set to
> > 0,
> > but the entry is preserved in case the image reappears at a different
> > place
> > (moving files where the removal is noticed first)
> > 
> > Marcel
> > 
> > > Hello.
> > > 
> > > I was facing this error from past few days:
> > > 
> > > MariaDB [digikam]> update Albums set albumRoot=0 where id=10;
> > > 
> > > > ERROR 1452 (23000): Cannot add or update a child row: a foreign key
> > > > constraint fails (`digikam`.`Albums`, CONSTRAINT `Albums_AlbumRoot
> > > > s` FOREIGN KEY (`albumRoot`) REFERENCES `AlbumRoots` (`id`) ON DELETE
> > > > CASCADE ON UPDATE CASCADE)
> > > 
> > > I figured out that as 'id' is AlbumRoots table is not 0. So 'albumRoot'
> > 
> > in
> > 
> > > Images table can't be set to 0. This is I think the possible reason for
> > 
> > FK
> > 
> > > constraint failing.
> > > 
> > > I used this statement instead & it worked:
> > > 
> > > MariaDB [digikam]> update Albums set albumRoot=1 where id=10;
> > > 
> > > > Query OK, 0 rows affected (0.06 sec)
> > > > Rows matched: 1  Changed: 0  Warnings: 0
> > > 
> > > Please look into this.
> > > 
> > > Regards
> > > ᐧ
> > 
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