Event Subscriptions and Expressions

[Evan Hale]

Hello, 

I am trying to understand how expressions work in regards subscribing to events.

So far I have:

session.event_hub.subscribe('topic=ftrack.update', handle_event)

I am trying to filter an ftrack.update event to only capture when a status change occurs. I understand I can access the key value pairs in the event using "." notation. However whatever I try seems not to work.  If my event looks like the one below how would I access "statusid" inside of "changes"? Or even "statusid" inside of "keys"? I am not sure how to navigate past the list that is "entities" or "keys". I also see in the api documentation that you can use ">" "<" operators. How would this work? I don't seem to be able to filter by length.

TLDR: I want to filter the event subscription to only capture events with a status change. How would I do this? Thanks!

"<Event"{
    "id":"9573a292408342b580dacfb654dd8a45",
    "data":{
       "entities":[
          {
             "entity_type":"Task",
             "keys":[
                "statusid"
             ],
             "objectTypeId":"11c137c0-ee7e-4f9c-91c5-8c77cec22b2c",
             "entityType":"task",
             "parents":[
                {
                   "entityId":"849a05ce-a267-11ed-8a5f-32d516aa59c4",
                   "entityType":"task",
                   "entity_type":"Task",
                   "parentId":"7c90fdb0-a267-11ed-8d96-32d516aa59c4"
                },
                {
                   "entityId":"7c90fdb0-a267-11ed-8d96-32d516aa59c4",
                   "entityType":"task",
                   "entity_type":"Folder",
                   "parentId":"829bf916-9cf5-11ed-b339-32d516aa59c4"
                },
                {
                   "entityId":"829bf916-9cf5-11ed-b339-32d516aa59c4",
                   "entityType":"show",
                   "entity_type":"Project",
                   "parentId":"None"
                }
             ],
             "parentId":"7c90fdb0-a267-11ed-8d96-32d516aa59c4",
             "action":"update",
             "entityId":"849a05ce-a267-11ed-8a5f-32d516aa59c4",
             "changes":{
                "statusid":{
                   "new":"44de097a-4164-11df-9218-0019bb4983d8",
                   "old":"44ddd0fe-4164-11df-9218-0019bb4983d8"
                }
             }
          }
       ],
       "pushToken":"6902c5b6-a3f3-11ed-8a5f-32d516aa59c4",
       "parents":[
          "7c90fdb0-a267-11ed-8d96-32d516aa59c4",
          "849a05ce-a267-11ed-8a5f-32d516aa59c4",
          "829bf916-9cf5-11ed-b339-32d516aa59c4"
       ],
    },
    "topic":"ftrack.update",
    "sent":"None",
    "source":{
    "target":"",
    "in_reply_to_event":"None"
 }">"

 

[Patrick Boucher ftrack]

Hi Evan,

Which documentation are you referring to that mentions `<` and `>`? I want to check it out and ensure it accurately reflects current capabilities.

As for your initial question, it is my understanding that anything past the boundary of a list is not accessible via the dot notation in a subscription. This would preclude you from accessing `changes.statusid.<new|old>` and `keys.statusid`. These kinds of things need to be implemented in your callback.

Regards,
Patrick

[Evan Hale]

Hey Patrick,

Sorry for the late response. I ended up doing exactly that and just filtering the events in the callback. I for the life of me cannot find the documentation where '<' and '>' operators can be used for filtering so maybe it was some old information or I am just going insane. Either way, I believe we are doing it the intended way in the callback now.

Thank you!