layerObj.getFeature seems to return a copy not a reference

[russell@…]

Using MapScript 4.10 on windows

layerObj.getFeature seems to return a copy, not a reference.

I call getFeature and change the annotation on the feature.  I can see that 
the text property changes.  I then call getFeature again with the same index 
and I get a feature with the original annotation.  I updated a copy.

It would be nice to get a real reference so I can edit the feature, would also 
be nice to have a method for removing features.

[sdlime]

A reference directly to a feature in a shapefile or database isn't possible. 
You always end up working with a copy and then would need to somehow commit 
your changes. MapServer hasn't gone that far and probably won't in the near 
future. Basically each driver would need to support an update method and the 
presents a number of challenges. For example, it is probably possible to edit 
the attrubutes of a shapefile in place, but you can't do that on the spatial 
side. You must re-write the whole file in that case.

Note that you often have the tools to do this outside of MapServer within the 
scripting language now.

Marking as something to look at in the future.

Steve

[sdlime]

A reference directly to a feature in a shapefile or database isn't possible. 
You always end up working with a copy and then would need to somehow commit 
your changes. MapServer hasn't gone that far and probably won't in the near 
future. Basically each driver would need to support an update method and the 
presents a number of challenges. For example, it is probably possible to edit 
the attrubutes of a shapefile in place, but you can't do that on the spatial 
side. You must re-write the whole file in that case.

Note that you often have the tools to do this outside of MapServer within the 
scripting language now.

Marking as something to look at in the future.

Steve

[russell@…]

[FURTHER EXPLANATION]

I'm working with inline
features defined in the mapfile.  I don't believe the layer feature
collection gives access to shapefile or database features.

layerObj.addFeature
layerObj.getNumFeatures
layerObj.getFeature

seem to work together and refer specifically to INLINE features.

getNumFeatures throws "msLayerGetNumFeatures(): Shapefile error. Not an
inline layer" if the layer is not an inline layer. 

addFeature works, and added features are displayed on the map. 

I'm not looking to edit the map file by editing a feature, just to
modify what is displayed on the map for an inline feature.

[RESPONSE FROM STEVE]

 I didn't
realize you were talking inline features only.

getFeature works for all connection types which makes it difficult to
do what you're asking. Only addFeature is limited to inline layers.
getNumFeatures only works for inline layers but that's because other
drivers haven't registered an equivalent.

[szekerest]

In fact mapserver handles the various data providers uniquely the returned
shapeObj-s are owned by the caller who is responsible to destroy the shapes.
The various drivers normally  does not retain or cache the shapeObj-s so
retrieving the shape by reference was not too relevant except for the inline layers.

However since I'm thinking of an addition that would provide a feature cache for
the various data providers this problem also gets some actuality. The long
running processes being capable to maintain the state of the mapscript objects
would happy to have a possibility to modify these shapes occasionally.

To provide some solution it would be desirable to make an additional function
like layer.GetShapeRef() in the layerObj vtable. This function would return the
shapes by reference and the caller would not destroy the underlying shape.

Tamas