Suppose I have a CF that holds some sort of assets that some users of my program have access to, and that some do not. In SQL-ish terms it would look something like this:
TABLE Assets ( asset_id serial primary key, ... ); TABLE Users ( user_id serial primary key, user_name text ); TABLE Permissions ( asset_id integer references(Assets), user_id integer references(Users) ) Now, I can generate UUIDs for my asset keys without any trouble, so the serial that I have in my pseudo-SQL Assets table isn't a problem. My problem is that I can't see a good way to model the relationship between user ids and assets. I see one way to do this, which has problems, and I think I sort of see a second way. The obvious way to do it is have the Assets CF have a SuperColumn that somehow enumerates the users allowed to see it, so when retrieving a specific Asset I can retrieve the users list and ensure that the user doing the request is allowed to see it. This has quite a few problems. The foremost is that Cassandra doesn't appear to have much for conflict resolution (at least I can't find any docs on it), so if two processes try to add permissions to the same Asset, it looks like one process will win and I have no idea what happens to the loser. Another problem is that Cassandra's SuperColumns don't appear to be ideal for storing lists of things; they store maps, which isn't a terrible problem, but it feels like a bit of a mismatch in my design. A SuperColumn mapping from user_ids to an empty byte array seems like it should work pretty efficiently for checking whether a user has permissions on an Asset, but it also seems pretty evil. The other idea that I have is a seperate CF for AssetPermissions that somehow stores pairs of asset_ids and user_names. I don't know what I'd use for a key in that situation, so I haven't really gotten too far in seeing what else is broken with that idea. I think it would get around the race condition, but I don't know how to do it, and I'm not sure how efficient it could be. What do people normally use in this situation? I assume it's a pretty common problem, but I haven't see it in the various data modelling examples on the Wiki.
