What are the alternative ways to model M:M relations in Cassandra?

Question

Consider a M:M relation that needs to be represented in a Cassandra data store.

What M:M modeling options are available? For each alternative, when is it to prefer? What M:M modeling choices have you made in your Cassandra powered projects?

Answer 1

Instead of using a join table the way you would with an rdbms, you would have one ColumnFamily containing a row for each X and a list of Ys associated with it, then a CF containing a row for each Y and a list of each X associated with it.

If it turns out you don't really care about querying one of those directions then only keep the CF that you do care about.