[Qgis-developer] Visualisation of relations

[Patrick Valsecchi]

Hi,

I'm tasked with making QGIS a bit more usable with complex database schemas
having a lot of relations (up to hundreds of linked tables). The INSPIRE
people were a bit too inspired when creating their data schemas and now we
have to try to make QGIS able to cope with that.

My concerns with the current situation (as of QGIS master) are:

   - We can specify the relations between the layers at the project level
   (it's now easier with the auto-discover feature for PostGIS and
   Spatialite). But those are only showing in the QgsAttributeForm for the 1-N
   side (the side that doesn't have the foreign key). Why not on the N-1 side?
   - For showing the N-1 side in the QgsAttributeForm, one can define a
   Join in the layer's properties, but I don't see the point of having to
   define it here as well when we have already the relations info at the
   project level. I see a use for special joins, but for relations, I don't
   see why we have to define it twice. And the way it's displayed is not
   allowing to create joins or edit the joined fields.
   - I let you imagine the look of the feature attribute form when there
   are hundreds of directly and indirectly linked tabled. This is just not
   usable if we display all of them directly like that. Just look at the
   attached screen shot that shows what happens by default with only 3 tables.
   It's already a mess.

Now, what I propose is:

   - Not expand the relation widget (QgsCollapsibleGroupBox) by default and
   build it's content only when it is expanded the first time (think of what
   would happen when you have loops in the schema).
   - Show N-1 relations as well, in a collapsed by default
   QgsCollapsibleGroupBox, including a way to add a new linked entry, remove
   the link (put the FK to NULL) and delete it.
   - Add a button to open a related feature in a new window.

What do you guys think?

Thanks.
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