[QGIS-Developer] Question over capability of adding to or editing a filtered shapefile

[Patrick Dunford]

Good evening

It seems there may be some point of contention over whether a shapefile 
that is filtered should be capable of having new features added.

I have recently begun filtering my shapefiles (to enable me to produce 
different views of the same map) and did not understand there might be a 
question over adding new features to a table that is filtered for 
display. To me this is like a discussion about live queries as opposed 
to static views of database queries, and whether the dataset should be 
capable of being updated for display when changes are made to it. It 
would seem the case is the same for editing filtered shapefile data, 
since this also involves a change to the source dataset.

There seems to be a design assumption that it shouldn't be possible to 
edit filtered shapefiles. Nevertheless, it is possible. I would like to 
ask for the rationale to be justified that it shouldn't be possible to 
edit a filtered shapefile. This seems to revolve around the question of 
whether the filtered view is meant to be read only or updateable.

In some of my maps I use filtering to present different (historical 
eras) views of the same geographical location, by filtering on a 
specific field, but this is also useful when editing the map, and this 
is what I am using at present with some maps I am working on. Currently 
the software appears to be geared around attempting to block edits or 
updates to a filtered shapefile dataset, but if present, this feature 
has only been introduced this year in Qgis 3.0.