There are page select and fileset select attributes in the marketplace, but no user select attributes.

Either the page or fileset select attribute may be a good starting point for coding a new attribute type, swapping out the page/file picker widget for a user picker widget.

Attributes can be quite simple to code, but the documentation, examples and hence general community wisdom is no-where near as good as it is for coding blocks, especially as it all changed for v8.

Thank you for the reply.
I used the link below to create a custom user attribute:
https://documentation.concrete5.org/developers/attributes/creating-c...

That sure seems like a lot of work for something functionally fairly simple, and a real pain if you wanted to add more values in the future.

I'd love to hear more about what hereNT mentions at the bottom of that page:

hereNT | Posted on Dec 31, 2016

I've used this technique extending the number attribute for years, it's been handy on tons of sites. The only real difference was that I didn't make up any kind of custom object for the dropdown values, instead just used a basic database query for name / id. Sometimes that's all you really need for a quick and dirty attribute type in an application.

There's not much to it, really. Just extending the number or text attribute and overriding the form to have a dropdown menu that's hardcoded or comes from a database table. I admit it's been awhile since I had to use it, so I don't remember many specific use cases but know that it's been handy when a full blown select doesn't make sense, or if there's a table that needs to be joined through.

Huh. Apparently I made a tutorial package showing how to do it. Completely forgot about that.

https://github.com/herent/c5_tutorials_database_attribute...

I am looking to do this exact same thing as you describe in your original post (attach one user to another user). Would you mind sharing a little more information as to how you accomplished this?