问题
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?
回答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.
回答2:
Cassandra by design is Key value database, so to achieve M:M there are two ways to do it.
De-normalize your data so every relation ship should duplicate data.
ie. x->y(value) and x->z(value) and a->y(value)
y should be saved for x and a
This is how it should be done as it's give you strength of database
Save reference for relational key as value.
x->y(key) and x->z(Key) and a->y(Key)
So if you need x with value of y it should be two operation, get x which will give you value of y. Then get y itself in a separate operation.
Cassandra is not RDBMS so don't wrap you mind around traditional way of doing it by dropping values and define relationship.
来源：https://stackoverflow.com/questions/2573106/what-are-the-alternative-ways-to-model-mm-relations-in-cassandra