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Re: [udig-devel] Re: [udig-users] ID of FID
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On Mon, Mar 17, 2008 at 5:06 PM, Jody Garnett <jgarnett@xxxxxxxxxxxxxxx> wrote:
> > Hi, I'm taking this to the devel list, since I also need some clarification.
> > Am I right in saying that the primary key column is taken as the FID field?
> >
> Depends which DataStore; you can also have multiple primary keys - for
> details see the JDBCDataStore FidMapper class.
I wonder what in that case is done.
> > This, in my opinion brings to different behaviours.
> > Imagine I have a postgis table with 4 fields, one of which is primary key.
> > case 1: I load it into udig through the postgis connection. Then I
> > export the layer to shapefile and what I gain is a file containing
> > only 3 fields, since the original primary key field was transformed
> > into FID and therefore distorting it, and also the FID is not
> > exported.
> >
> > case 2: I export the shapefile through pgsql3shp. I get my nice
> > shapefile with all 4 fields.
> >
> > Is this a known behaviour? Is this a proper behaviour?
> >
> It is up to you the developer what you want to do; some file based
> datastore formats can store the feature id you provided (the property
> datastore can for example); others like shapefile have a very simple
> definition of primary key (ie row number).
Not sure here. As a developer in these "standard" things I want to
rely on the "standard" tools of the application and not fork some
stuff and then maintain a fork.
> > I have a strange feeling in knowing that I will lose a field in exporting a postgis layer through udig.
> >
> Please note that if you import the shapefile you exported as pgsql3shp
> you will have 4 fields AND a primary key (so 5 bits of information).
> If your table had an ID column that was not a primary key I think the
> default behavior is to use the "oid" information for the row - which is
> only stable for rows that have not been updated or something.
I agree about that, but anyway for the shapefiles the fid is never
stable, since every time I edit and save, the fid column is refreshed
and the original fid table is lost.
So in the case I export a shapefile from postgis, the primary key
column is changed from int to a string and every time I edit, the id
mapping is no more the same as the original. I'm just asking for
information.
> I think you can set a Hint or configuration option to include keys as
> readable attributes (up to you).
Again, I would not want to fork anything. Is this what you mean?
Ciao
Andrea
> Jody
> _______________________________________________
> User-friendly Desktop Internet GIS (uDig)
> http://udig.refractions.net
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