How do I filter the list of changes when subscribing to a model?

[hishnash]

How do I filter the list of changes when subscribing to a model?

[hishnash]

You should use the @model_observer.

Let us consider the example of subscribing to all the comments that @mention the current user.

To start out we can declare the model observer handler method:

@model_observer(Comment)
async def blog_post_comment_changed(self, message, subscribed_request_ids,  action, **kwargs):
    await self.reply(action=action, data= message, request_id=request_id)

With this in place we need to add an action to our consumer so that the user can start subscribing to changes.

@action()
async def subscribe_to_comments(self, request_id, **kwargs):
    username = self.scope['user'].username
    await  self. blog_post_comment_changed.subscribe(request_id=request_id, username=username)
    await self.reply(action=action, request_id=request_id)

Important in the above snippet is the passing of the username to the subscribe method. This allows us to use it when enumerating which channel groups to subscribe to.

To do this we add a groups_for_consumer method

@blog_post_comment_changed.groups_for_consumer
def blog_post_comment_changed(self, username: str, **kwargs):
    yield f"mentioned__{username}"
    yield f"reply_to__{username}"

This method is called when subscribing to enumerate the list of groups to subscribe to. In this case we subscribe to 2 different groups. The first is a group that will get notified every time a user @mentions the user by username the second is a group that will be notified every time a direct reply is created.

With the consumer subscribe to these 2 groups we now need to ensure that when a Comment is created/edited/deleted we send a message to the correct groups.

To do this we implement a groups_for_signal method this is called every time any Comment is created/edited or deleted.

def blog_post_comment_changed(self, instance: Comment, **kwargs):
    for mention in comment.get_mentions():
        yield f'mentioned__{mention.username}'
    
    parent = instance.parent
    if parent is not None and instance.author != parent.author:
        yield f"reply_to__{parent.author.username}"