if you want to look up "what permissions does user X have on asset Y" then i would model that as a row keyed by userid, containing supercolumns named by asset ids, and containing subcolumns of the permissions granted.
On Mon, Apr 19, 2010 at 12:03 PM, tsuraan <tsur...@gmail.com> wrote: > 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. >
