[Qgis-developer] Memory data provider persistence

[Chris Crook]

Hi

I think the change in behaviour is due to the change in the gdal 1.9 implementation of the GML driver, which generates the fid field when the layer is reloaded.  I am looking at a fix that basically removes the field after it is reloaded.
Not an ideal solution (especially if you want a field called "fid").

On you other points on the memory layer saving, it may be worth reviewing the earlier discussions about the memory layer saver.

http://lists.osgeo.org/pipermail/qgis-developer/2010-December/011876.html

I have a couple of times proposed that memory layers get saved alongside the project or within the project file.  Inside the project file is not a good idea - it could easily get too big.  

So the main question for the ideal solution is how to store the information.  I am using the GML format as a preferrred open format (preferred in this case based on responese on the qgis dev list).  I'm inclined to modify this to a format that uses a single file for all the layers as a cleaner implementation from the users perspective (eg if the project file is test.qgs then the persisted data is in test.qgs.db, or something like that).  The format could be spatialite perhaps, or a zip file of the gml files?  It would also get rid of the horrible long file names.

I see in your bug post that you have found that sometimes the layers don't get saved at all.  I haven't experienced this, but I did notice that if you start editing a layer, add some features, and then quit qgis without saving the edits, then there is no prompt for saving the edits.  If the edits don't get saved then the memory saver plugin doesn't flag the project as dirty, and so the changes don't get saved.  Could this match your example?

Cheers
Chris Crook


-----Original Message-----
From: haubourg [mailto:regis.haubourg at eau-adour-garonne.fr] 
Sent: Saturday, 21 July 2012 1:55 a.m.
To: qgis-developer at lists.osgeo.org
Subject: Re: [Qgis-developer] Memory data provider persistence

Hi all,
one up for this topic. Since QGIS 1.8, memory layer saver is not working the same way as in 1.7.4.
I raised a tickets here  http://hub.qgis.org/issues/6075
http://hub.qgis.org/issues/6075 , but I think something changed in memory layer provider or OGR GML provider, and it maybe isn't a plugin issue:

In fact, FID field was previously hidden to end user in QGIS but was present in GML.  It was filled with "F"+id . It now is filled with "projectName."+id. FID field is now shown to end user whic alterates table structure when saving. 
Reopening project, saving and reoping a second time add a second FID field. 

Anyone has an idea of what's going on ? 

BTW *I'am really interested to have a stable way of saving memory layers along with project.Anyone still working on it ? Having it part of the Core would be great too. I am ready to sponsor it since it. * What solution should we keep? gml+xsd along with project? A dialog asking what memory layers to save, and explaining what are thoses gml and xsd files would be nice too. I have seen users cleaning up those messy files since they did not understand what they were.. 




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