Tnx. I found your blog post already before and it gives a good background but am looking for something lower level. More of “how does one work with it”. I know the Ecto docs are there so explicitly excluded them in the question 
Found also this thread: Ecto associations and the purpose of has many through and many to many But still - do I need to take low level care of things (transactional creating of join records for example like the OP there does) or are there some built-in mechanisms / “best practices” that I’d be best aware of before I create lots of completely unneeded code
