Assign existing property group to a new collection

Question

I have a propertygroup class called "Variants" from which I created several variant objects. Now I'm struggling to add these existing objects to a collection in another class.

class variantStates(bpy.types.PropertyGroup):

    variantState: bpy.props.StringProperty()

class variant(bpy.types.PropertyGroup):

    variantType: bpy.props.StringProperty()
    variantName: bpy.props.StringProperty()
    # List of all possible states
    variantStates: bpy.props.CollectionProperty(type=variantStates)


class variantList(bpy.types.PropertyGroup):

    variantRef: bpy.props.PointerProperty(type=variant)


class variantSet(bpy.types.PropertyGroup):
    # This is a Variant Set. It will contain several variants and trigger them all together

    variantSetName: bpy.props.StringProperty()

    # Here I want to add the existing variants when I create the set
    variantSetVariants: bpy.props.CollectionProperty(type=variantList)

here is the snippet from the operator that should later add the variants to the set:

for variant in var:
    
        addedVariant = newSet.variantSetVariants.add()
        addedVariant.variantRef = variant

I use the same approach as with adding the states to the variant early, but now it tells me that the pointer is read-only. And I only get a new empty variant added to the list. I guess I'm not really knowing what the pointer does. How can I achieve this? I was following the logic of this post where this is done with a pointer to "bpy.types.Object" and it works perfectly:

How to get one UIList to control the contents of another UIList?

Answer 1

You can't do that : addedVariant.variantRef = variant

It is not possible to reassign a PointerProperty.

You'll have to manually copy the properties from the reference property group to the target property group.

eg

for variant in var:    
    addedVariant = newSet.variantSetVariants.add()
    addedVariant.variantRef.variantType = variant.variantType
    addedVariant.variantRef.variantName = variant.variantName
    # etc.
    # It's a bit more involved to copy collection properties
    addedVariant.variantRef.variantStates.clear() # Ensure it's empty before copying
    for source_state in variant.variantStates:
        new_state = addedVariant.variantRef.variantStates.add()
        new_state.name = source_state.name  # This attribute is builtin. (no need to explicitely define it)
        new_state.variantState = source_state.variantState
        # etc.