Developer Forum

Where to find collection_index for moving an object?

Other Development Topics Python API
#1

Hey guys,

in preparing my addon for 2.8 I try to make the necessary collections and move or link objects into them via

bpy.ops.object.move_to_collection(collection_index=n)

I thought the collection_index=n would be the index of bpy.data.collections[n], which you can find by bpy.data.collections.find(“CollectionName”), but its not.

I figured out that bpy.data.collections are reordered alphabetically when a new collection is added or a collection is renamed. But the collection_index key of the move_to_collection function is an index given in order of collection creation. Can someone tell me how to access the collection_index value (preferably by collection name)?

Addon Operators and Undo support
#2

Do not use operators for moving objects between collections. In general operators are not reliable to use in scripts, they are meant as end user tools. These indices correspond to a particular layout in user interface menus.

Instead use collection.objects.link() and collection.objects.unlink() API functions.
https://docs.blender.org/api/blender2.8/bpy.types.CollectionObjects.html

2 Likes
#3

thank you, for the fast answer. This works great :see_no_evil::hear_no_evil::speak_no_evil:

#4

hmmm…sorry to bother again. I guess my limited python is in my way, but I could only figure out half of the clue

I see that I better use code like this to move objects reliably to a specific collection (if thats what you meant):
bpy.data.colllections[“CollectionName”].objects.link(bpy.data.objects[Objectname])

However, I could not figure out how to create, remove, move and instance collections.
I could only find these operators:

bpy.ops.collection.create(name=“Collection”) … which creates a collection with the given name, which i can find by data.collections[’’]. but it doesn’t appear in the outliner.

yes the dirty one makes collections, too, but with the problems mentioned above
bpy.ops.object.move_to_collection(collection_index=n)

bpy.data.collections.remove(bpy.data.collections[‘CollName’]) removes the collection from bpy.data.collections-list. But than blender crashes when I hover over the outliner… I guess I delete from the wrong spot and its not updated…???

moving and instancing is even more a riddle to me.

Could you give me another hint how to approach these things?

thx in advance

#5

Some examples:

# Create new collection
collection = bpy.data.collections.new(name="MyCollection")

# Add collection to scene
scene.collection.children.link(collection)

# Create collection instance in scene
object = bpy.data.objects.new(name="MyObject", object_data=None)
object.instance_collection = collection
scene.collection.objects.link(object)
3 Likes