CollectionProperty avoid duplicate names

Question

I have a CollectionProperty like this:

class RenderGroups(PropertyGroup):
    image = StringProperty(name="Image", description="The image-texture of this group")

class MHFCMeshProps(PropertyGroup):
    render_groups = CollectionProperty(type=RenderGroups,
                                       name="Render Groups")

Now I don't want duplicate names in the PropertyGroup but I stumbled when I tried to shadow the internal name with a StringProperty. Is there any way the following code:

g = obj.testgroup.render_groups.add()
g.name = "Name"
g = obj.testgroup.render_groups.add()
g.name = "Name"

would result in two different keys "Name" and "Name.001" for example?

Answer 1

Here is my idea: Overwrite the attribute setting function of the class. The following code has been created mostly be the OP, based on that idea. I added some minor formatting for better readability:

import bpy
import re
from bpy.props import *

unique_names = ['name']

class RenderGroups(bpy.types.PropertyGroup):
    image = StringProperty(
            name="Image", 
            description="The image-texture of this group")

    def __setattr__(self, name, value): 

        def collection_from_element(self):
            # this gets the collection that the element is in
            path = self.path_from_id()
            match = re.match('(.*)\[\d*\]', path)
            parent = self.id_data
            try:
                coll_path = match.group(1)
            except AttributeError:
                raise TypeError("Propery not element in a collection.") 
            else:
                return parent.path_resolve(coll_path)

        def new_val(stem, nbr):
            # simply for formatting
            return '{st}.{nbr:03d}'.format(st=stem, nbr=nbr)

        # =====================================================

        if name not in unique_names:
            # don't want to handle
            self[name] = value
            return
        if value == getattr(self, name):
            # check for assignement of current value
            return

        coll = collection_from_element(self)
        if value not in coll:
            # if value is not in the collection, just assign
            self[name] = value
            return

        # see if value is already in a format like 'name.012'
        match = re.match('(.*)\.(\d{3,})', value)
        if match is None:
            stem, nbr = value, 1
        else:
            stem, nbr = match.groups()

        # check for each value if in collection
        new_value = new_val(stem, nbr)
        while new_value in coll:
            nbr += 1
            new_value = new_val(stem, nbr)
        self[name] = new_value

class MHFCMeshProps(bpy.types.PropertyGroup):
    render_groups = CollectionProperty(
            type=RenderGroups,
            name="Render Groups")

if __name__ == "__main__":
    bpy.utils.register_class(RenderGroups)
    bpy.utils.register_class(MHFCMeshProps)
    bpy.types.Object.testprop = PointerProperty(type=MHFCMeshProps)

Now you can do this in the blender python console:

obj=bpy.context.object
g=obj.testprop .render_groups.add()
g.name, g.whatever="testme", "keepme"
g.name, g['whatever']
('testme', 'keepme')

g=obj.testprop .render_groups.add()
g.name, g.whatever="testme", "keepme"
g.name, g['whatever']
('testme.001', 'keepme')

I think the code example above is now pretty much complete. Although there is still one caveat here. This keeps track of reassigning the current value and always assigns the lowest nbr possible.

Answer 2

There is no way with the api I think. I would suggest to implement your own function:

#collection:    collection, where you want to add a new entry
#name:          the 'original' name, will maybe modified
def add_new(collection, name): #or add_unique is maybe better
    #check if name allready exists in the given collection
    #if not add it directly
    if name in collection:
        try:
            #check if the name has allready a number
            #if not this will produce an error and except will be executed
            if name[-4:-3] == '.': #check for a point
                int(name[-3:])
                #cut out the 'original' name
                #([:-4] remove last 4 chars)
                name = name[:-4]
        except:
            #if its not an integer, do nothing
            pass

        i = 1
        #generate three chars with '0' ('{:0>3}') and
        #replace it with the next number (.format)
        #until a free number is found
        while (name + '.{:0>3}'.format(str(i))) in collection:
            #otherwise continue counting
            i += 1
        #add number to name
        name = name + '.{:0>3}'.format(str(i))
    #finally add item
    itm = collection.add()
    # ... and assign name
    itm.name = name
    #return that item
    return itm

Then you can use this in your code:

g = add_new(obj.testgroup.render_groups, "Name")
#->g.name= "Name"

g = add_new(obj.testgroup.render_groups, "Name")
#->g.name= "Name.001"

g = add_new(obj.testgroup.render_groups, "Name.001")
#->g.name= "Name.002" not "Name.001.001"