Named Groups

Named Groups provide a way for a MicroStation user to connect logically a set of MicroStation graphic elements. Named groups can include elements from the active file and those from directly attached references. Elements in a named group can be manipulated collectively: read MicroStation help for more information. The MicroStation user interface makes it easy to create a named group and add and remove elements in that group …

Nested Named Groups

As well as individual named groups, you can create a hierarchy of them by adding “child” named groups to a “parent”. When you have a hierarchy, manipulating the “parent” named group will include any attached “child” named groups. You can add and drop elements from individual named groups (including those that are part of a hierarchy), as well as manipulate the elements within each named group (again, including those that are part of a hierarchy).

Programming Named Groups

Get the named groups collection for a specified DGN model like this …

dgn_model: DgnModel = ISessionMgr.ActiveDgnModelRef
named_groups = NamedGroupCollection(dgn_model)

Enumerate that collection to see each named group …

count = 0
for i, group in enumerate(named_groups):
    msg += f"  [{1 + i}] Name: {group.GetName()}, Description: {group.GetDescription()}\n"
    count = i + 1

You can create, modify, and delete named groups using the Python API.

You can visit members of a named group using the TraverseMembers() and TraverseRelatedMembers() functions.

Get the size of a NamedGroupCollection like this …

n_groups = len(list(named_groups))

Named Group Collection Problem

Warning: Don't assume that you can convert a NamedGroupedCollection to a Python list

If you take this reasonable step and then attempt to enumerate the resulting list, it won't work. Something happens in the conversion and the data become garbled …

dgn_model: DgnModel = ISessionMgr.ActiveDgnModelRef
named_groups = NamedGroupCollection(dgn_model)
named_group_list = list(named_groups)
for group in named_group_list:
    name = group.GetName() # Gives odd error message

The NamedGroupCollection is not Pythonic: it has no __len__() member and no __iter__() method. We get its length by converting it to a list and measuring the length of that list …

n_members = len(list(named_group_collection))

But don't attempt to use that list for enumeration! See what follows …

The lack of an iteration (__iter__()) method means that we can't use the usual Python ways to enumerate that list. That's one reason I wrote NamedGroupProxy. Here's how to get a list of NamedGroupProxy from a NamedGroupCollection …

def named_group_collection_to_list(named_group_collection: NamedGroupCollection)->(int, list[NamedGroupProxy]):
    '''
    Convert a NamedGroupCollection to a Python list.

    Returns: tuple (int, list[NamedGroupProxy])
    '''
    dgn_model = named_group_collection.GetModelRef().GetDgnModel()
    ng_list = []

    for i, group in enumerate (named_group_collection):
        proxy = NamedGroupProxy.from_named_group(group, dgn_model)
        #print(f"[{i}] {proxy}") # For developers only
        ng_list.append(proxy)
    return len(ng_list), ng_list

Named Group Flags

Class NamedGroupFlags get/sets various named flags that specify such things as propagation protocols. They are described in the Named Group Flags page.

Questions

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