[Qgis-developer] Re: qgsRelate (Table joins in QGIS)

Maurício de Paulo mauricio.dev at gmail.com
Sun Dec 27 13:41:13 EST 2009

The idea behind this plugin is that it would use qgsvectorlayer  (that
supports shapefile, postgresql, grass, dbf, etc) and would join only a
single feature attributes.
So i'm proposing that the user would select a feature and would be able to
find everything related to it. Every relationship could be stored in a
relationship file so that you could reproduce it for a given data model.
It's a major problem in Brasil because we defined a new spatial model and
qgis is not able to read relationships. At least, the user should be able to
build them to look for non-spatial relations of a given feature.
Well, as soon as I have a working plugin i'm going to release it. If anyone
have interest in it, please tell me so I can continue working without
loosing my time. :P
Mauricio de Paulo

2009/12/27 John C. Tull <john.tull at wildnevada.org>

> Hi Mauricio,
> I am interested in what you propose. Currently, fTools allows joining
> tables using dbf files (maybe other formats, not sure). But this produces a
> new shapefile. Having a means to create table joins without outputting a new
> file would be very useful. I am sure others would agree. Ideally, this would
> allow the use of multiple table formats, including postgresql, as you
> suggested.
> Cheers,
> John
> On Dec 26, 2009, at 8:56 PM, Maurício de Paulo wrote:
> Well, after some testing I found out that qgis now can open dbf files as
> vector layers. It's enough for me to create the "relate" implementation.
> As far as I can see, it's possible and won't take too long to implement.
> Will it be usefull? Is anyone already working on a full join implementation?
> Mauricio de Paulo
> 2009/12/26 Maurício de Paulo <mauricio.dev at gmail.com>
>> Hi folks,
>> I don't remember exactly what was defined on the last discussion about
>> table joins.
>> I've read many good sugestions, many of them about implementing attribute
>> relationship inside qgsvectorprovider.
>> I also work on ArcGIS and the relations and joins on ArcGIS usually don't
>> show the full table join. It only shows the related attributes of a single
>> feature. So for each feature, you can use a Info tool to see every attribute
>> about it (including the ones that comes from related tables). Everything is
>> done on the fly, but performance is not a big issue as i'm only going to
>> search for one feature's relationships.
>> I'm using the screenshots that are attached to the mail as an example of
>> how it should work.
>> At the moment I need some feedback on what it is or is not a good approach
>> and if it's gonna be usefull for the users.
>> What do you guys think?
>> The idea is a plugin to record what relationships are stored for each
>> layer and then show the attributes in a tree view where a single feature can
>> be linked to many other rows in the second table. I still don't know how i'm
>> going to implement it but either I will use ogr or qgsvectorprovider. I
>> still have to search if it's possible to access the dbf files and postgis
>> connections using qgis api.
>> Any comment is welcome.
>> Mauricio de Paulo
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