Use the layer type when adding a part to a featureless entry. Fix #8459

[biolds]

Fix http://hub.qgis.org/issues/8459

[3nids]

@mhugent can you have a look to this?

[biolds]

I should explain a bit:
Adding a new part to a empty geometry fails because the type of geometry (created in QgsVectorLayerEditUtils::addPart) is UnknownGeometry. Adding a part to this type of geometry fails in QgsGeometry::addPart, because the code relies on it to check the added part.
This patch adds an argument to addPart to allow passing the type that we know from the layer.

[mhugent]

Could you explain a bit more on the use case? I assume there is a specific reason why you add a part to an empty geometry (instead creating a new geometry).
Also, is it possible to test the geometry type ( and do fromGeos() if unknown) at the begin of the function instead of passing the geometry type as an argument?

[3nids]

Basically if you already have a feature without any geometry and want to edit it. If it's a multi part, I think the most obvious way is to use add part.

The question for single geometry would still be open.

[mhugent]

Right, that sounds reasonable for single and multi types.
Is it possible to just alter the behaviour of addPart() function such that the part becomes the geometry if geometry is empty (so without the need to pass a type as an argument to the function)?

[biolds]

Both for multi part type and single part the "Add part" button can be used to set the geometry, I think they are handled the same way in Qgis. I checked it works correctly with single and multi geometries.
In my use case, the database lines are created using an other software (Tryton, an ERP), and afterward I set geometries on these entries.
It's not possible to retrieve the type from the Geometry because it uses the underlying GEOS object to retrieve the type, and since it is NULL the Geometry has a type UnknownGeometry at this point.

[mhugent]

I see, we need the geometry type to create the part object. That's fine, patch is applied. Thank you !