[Bf-committers] About groups and object deletion in 2.77

Bastien Montagne montagne29 at wanadoo.fr
Sun Feb 21 17:22:42 CET 2016

Hi people,

So, a recent report [1] raised the topic of how deleting objects should 
(or not) remove them from their groups.

The 2.76 and previous behavior was (usually) to remove objects from 
their groups once they were deleted from all user scenes.
However, this behavior was broken in some cases (the 'user_one' ID 
issue, same as with images used in both textures and ImageEditor
e.g., depending on order of assignments images becomes unremovable…).

In 2.77 a fix was made to our handling of those 'user_one' ID usages, 
previous 'special behaviors' of those corner cases shall no more
exist, and usercount should always remain consistent.

Now, this unfold an issue with object deletion and groups: since 
'user_one' usage is no more 'lost' when deleting the object, it does not 
anymore from its groups - so you get an unreachable object still 
presents in all groups instantiations, which is obviously bad.

This kind of enlight our poor managing of objects & groups imho, but for 
2.77 I would propose to simply add explicit removal
of object from all groups uppon deletion (provided said object is used 
by no scene anymore). That way we avoid changing
behavior for users, and at least code also clearly reflects expected 

Later we can decide what tools we want to manage objects in groups, and 
add them. ;)

[1] https://developer.blender.org/T47482

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