Auto Populate with User ID?

Super excited that 1.5 is now available for cloud!

Question.. how do I set an attribute to auto populate with the user ID?

Or what’s the easiest way to have that linked?

depends on how you're creating the document.

For example, I have a users/profiles collection and a function that triggers when a new user is created. Then, i take that data and create the document in users/profiles collection

Just generally I wondered if it could be set as a default value or a trigger rather than having to be passed through as a value from a web app for example