[Digikam-devel] Update query fails
Swati Lodha
swatilodha27 at gmail.com
Thu Jun 2 19:26:12 BST 2016
Please find attached patch file for the same.
Thank you.
ᐧ
On Thu, Jun 2, 2016 at 8:57 PM, Swati Lodha <swatilodha27 at gmail.com> wrote:
> Hello
>
> In coredb.cpp:4547 ";" is missing after the UPDATE query. This change
> should be committed?
>
> Regards
> ᐧ
>
> On Wed, Jun 1, 2016 at 6:14 PM, Richard Mortimer <
> richm+digikam at oldelvet.org.uk> wrote:
>
>> On 01/06/2016 10:12, Swati Lodha wrote:
>> > I understand this now. Thank you for clarification.
>> >
>> > So as it mentioned around coredb.cpp:549
>> >
>> > 549 // We need to work around the table constraint, no we want to
>> > delete older stale albums with
>> > 550 // the same relativePath, and adjust relativePaths depending on
>> > albumRoot.
>> >
>> >
>> > I think that this needs to be done?
>>
>> It is all part of the bigger picture that needs considering to allow
>> referential integrity to be applied across the (MySQL) database. I don't
>> have the years of experience with digikam that Marcel does but I think
>> the following is required:
>>
>> 1 - apply "ideal" referential integrity to the MySQL digikam schema
>> (mostly done).
>>
>> 2 - now identify where things break down due to interaction with the
>> outside world (file systems, other photo editors/tools). Generally I
>> think this is easy to spot and is normally the root of an information
>> hierarchy. (tags tree, albums, album roots spring to mind).
>>
>> I think that digikam has been pretty consistent with using a magic "0"
>> value to represent where something no-longer fits into a hierarchy but
>> is likely to re-appear in due course.
>>
>> 3 - Once identified the architectural decision is how to handle it in a
>> database configured to enforce referential integrity. Bear in mind that
>> this needs to continue to support SQLite too without having to add too
>> many special cases. Note that SQLite is capable of supporting
>> referential integrity so the choice may be to adopt the same solution
>> for both.
>>
>> Really the choices for handling the orphaned items are:
>>
>> a - disable referential integrity on those affected fields. That is
>> almost trivial to implement but does negate some of the benefits.
>>
>> b - add "special" internal rows that can be used to collect these
>> temporarily orphaned nodes. I know that there is one at the root of the
>> tags tree for MySQL. Note they are a bit tricky to arrange because they
>> really need to be created with a primary key of zero to match the
>> existing behaviour of putting zero in there.
>>
>> c - change to use null instead of a magic placeholder value. That is
>> probably a purer solution but does create differences between SQLite and
>> MySQL.
>>
>> I'd probably suggest that option b is the right one to minimise chances
>> of short/medium term breakage but would be interested to know what
>> others think.
>>
>> Regards
>>
>> Richard
>>
>> P.S. even if b & c are chosen there are some potential issues that may
>> occur if multiple orphaned tags, folders, images have the same name.
>> That will trip up with existing "unique" constraints on the database. I
>> suspect that this should just be left as "good enough" for now.
>>
>>
>> >
>> > Regards
>> > ᐧ
>> >
>> > On Wed, Jun 1, 2016 at 2:28 PM, Marcel Wiesweg <marcel.wiesweg at gmx.de
>> > <mailto:marcel.wiesweg at gmx.de>> wrote:
>> >
>> > 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 <mailto: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
>> > > >
>> > > > _______________________________________________
>> > > > Digikam-devel mailing list
>> > > > Digikam-devel at kde.org <mailto:Digikam-devel at kde.org>
>> > > > https://mail.kde.org/mailman/listinfo/digikam-devel
>> >
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>> >
>> >
>> >
>> >
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