Subscribe

You can subscribe to object events using filters.

Use Cases

Subscription is a very powerful feature in Novi. It's crucial for some plugins. For example, I want to generate a thumbnail for every image object (yes, that's a plugin instead of a built-in feature in Novi). I can subscribe to image objects that have local files and generate thumbnails for them.

@=image @file:original -@file:thumbnail

The filter above subscribes to image objects that have original files but don't have thumbnail files. For each matching object, we generate thumbnail for it and add a @file:thumbnail property to it.

Here's another example. I want to automatically add a dog tag to every image object that has a corgi tag. I can use the following filter:

@=image corgi -dog

And for each matching object, we add a dog tag to it. However, this is not the best practice since we can achieve the same result using an imply rule.