[postgis-devel] triggers for postgis topology edition

[Rémi Cura]

Yep,
enabling/disabling seems necessary because as you said,
and is very easy to do (ALTER TABLE table DISABLE TRIGGER USER;)
enabling the trigger and importing data in topology would be at best slower,
, probably very hard to write
, and at worst impossible (infinite trigger call).

I also have the concurrent editing in mind, but I don't aim at doing an
un-breakable topology for my first try.
simply allowing reasonable edition in qgis, where the user understand
topology and doesn't break things:
 - edition not modifying topology : moving non-isolated node, changing geom
of edges (excluding first/last point, no crossing other edges)
 - edition modifying topology : create a node (split edge if necessary),
delete a node(heal edge if necessary), adding/deleting edged between
existing node

long term goal is more like un-breakable scenario and would be for the user
to simply edit a linestring layer, and the topology associated to this
layer would be updated,
which is a very common use case I believe, but much  more difficult to do
right .

Cheers,
Rémi-C

2015-02-05 12:44 GMT+01:00 Sandro Santilli <strk at keybit.net>:

> On Thu, Feb 05, 2015 at 12:34:18PM +0100, Rémi Cura wrote:
> > Hey,
> > I'm going to write triggers on postgis topology low level tables
> > (edge_data,node) to allow simple edition in QGIS without plug-in.
> > Anybody has something on it, or ideas?
>
> I've always avoided triggers as checking all conditions would be
> very expensive, and ISO editors are doing the checking themselves,
> which would make other triggers do the work twice.
>
> But on the other hand getting full triggers in place might make it
> impossible to break a topology by concurrent editing, which could
> be a nice feature to have. Maybe you could have functions to
> enable/disable such triggers to do some tests ?
>
> --strk;
>
>   ()   Free GIS & Flash consultant/developer
>   /\   http://strk.keybit.net/services.html
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