Relationship options: where, group by, display, order by

Hello,

I’m trying to customize options for admin post edit for Relationship field.

Here is what I haven’t found solution for in forums nor in documentation:

Display field in selection list: can I have 2 fields displayed in drop down list? I tried this and it doesn’t work: {@post_author}: {@post_title}

Customized WHERE: can I have current user filtered posts? I tried this but it doesn’t work: post_author={@post_author}

How can I define GROUP BY to sort list items by usernames like this for example:

John
– post title A
– post title X
James
– post title Y
– post title Z

I tried this but it doesn’t work: post_author.name