Expilitly identify each element of a server

[duxt3r]

Is there a way to identify each element of a server explicitly? Display names and node ids are repetitive. I'm just wondering if I need to implement this myself or if there is something like an uid or specific attribute each element carries.

[schroeder-]

NodeIds are unique. But in the browse tree it possible that a node is referenced(linked) by multiple other nodes.

[duxt3r]

so client.get_node() could result in getting the same id twice? If so, is there a way to differentiate those?

[schroeder-]

No. NodeId is unique, so get_node returns only one Node. But in the Browsetree a node could be found multiple times.

[AndreasHeine]

it depends on the used hierarchical reference...
a node can be referenced multiple times so it will appear multiple times!

X:Sensor -> 3:SignalSet has a child X:Temperature (ProcessValueType)
X:Temperature is also referenced under X:Monitoring!

so if you crawl the X:MyMachine it will find it twice as long as you dont apply filter to the browse where you can specify the references you want the BrowseResult for!

[duxt3r]

But if I go over all elements of the server with a recursive function I get the same nodeid output twice.

def get_server_recursive(client, parent):
    children = client.get_node(parent).get_children()
    if children:
        for child in children:
            child_id = client.get_node(child)
            print(child_id)
            get_server_tree_recursive(client, child)

EDIT:
Sorry @AndreasHeine , I didn't see your reply befor commenting.
That makes sense, thanks!

[AndreasHeine]

get_children -> makes a browse request! https://github.com/FreeOpcUa/python-opcua/blob/master/opcua/common/node.py#L294-L316

get_children(self, refs=ua.ObjectIds.HierarchicalReferences, nodeclassmask=ua.NodeClass.Unspecified):

which calls:
def get_referenced_nodes(self, refs=ua.ObjectIds.References, direction=ua.BrowseDirection.Both, nodeclassmask=ua.NodeClass.Unspecified, includesubtypes=True):

includesubtypes=True means all subtypes of "ua.ObjectIds.HierarchicalReferences"

ua.NodeClass:
https://github.com/FreeOpcUa/python-opcua/blob/master/opcua/ua/uaprotocol_auto.py#L356-L385

    Unspecified = 0
    Object = 1
    Variable = 2
    Method = 4
    ObjectType = 8
    VariableType = 16
    ReferenceType = 32
    DataType = 64
    View = 128