Model association

### I had problem with association with model Admin_User and Post.
I don't know how to get current user id when create a post.
I want the user id that is current id of login user(admin) will be inserted automatically when create a post.
``` 
form do |f|
    f.inputs "Post detail"  do 

      f.input :title
      f.input :content
      f.input :#user_id here
    end
    f.actions
  end

```