[QGIS-Developer] Run processing model on selected features only

[Nyall Dawson]

On 14 December 2017 at 17:45, Matthias Kuhn <matthias at opengis.ch> wrote:

>
> When relations are involved, there needs to be a vector layer around to
> work with these as far as I can see.
> If this vector layer is promoted from a feature source parameter or
> provided as vector layer input is a different question (I can live with
> both).

What I've been wondering is whether we need some concept of "original
layer id" in outputs generated by processing models. This could allow
us to retrieve relation information and additionally editor widget
config from the original source layer.

It's bound to be requested soon that someone wants to run a model that
does something like take a vector layer with a relation, change its
geometry in some way, and then do something with related features.
Regardless of whether we use vector layers or feature sources, that
just isn't possible in models currently since the output from any
other algorithms is a new layer, which has no knowledge of the
original layer's relations or editor widget config. (Also layer
metadata, which in some future release I'd like to see retained with
every step of a model)

I'm not sure the best way to handle this, but if it was available for
the output layers it would be trivial to make it also available for
feature sources, and through it allow models which use feature sources
to take advantage of relations/editor widget config/etc.

What do you think?

Nyall