On Apr 17, 3:16 pm, "Martin P. Hellwig" <martin.hell...@dcuktec.org> wrote: > Daniel Fetchinson wrote: > > <cut> > > > > > In an relational database setting you would have a table for artists, > > a table for cd's and a table for songs and a table for comments where > > people can comment on songs. All of this with obvious foreign keys. > > Now you want to display on your website the total number of cd's, the > > total number of songs and the total number of comments because that > > looks very cool on top of every page: 1242342 cd's and 134242342342 > > songs and 284284728347284728 comments! > > > Okay, so you need to issue a query with joins in your relational db. > > Or in another query, you want to select all comments of an artist, > > meaning all comments that were comments on a song belonging to cd's of > > a given artist. This would also involve joins. > > > How would I do these queries if I can't have joins or in other words > > how would I lay out my data storage? > > > Thanks by the way for your help and replies, > > Daniel > > What actually is happening here is that feature x which is usually in an > abstraction layer (like a RDBM) is not available to you. Which means you > have to write code which does the same but on your side of the code. > > I played a bit around with the GAE some time ago and designed the > storage of all data in an sort of EAV model > (http://en.wikipedia.org/wiki/Entity-Attribute-Value_model) > The abstraction layer had all my meta code, counting stuff up was a > matter of creating a list of id's from one section and with that list > selecting the appropriate records on the other section, then count up > the number of results or use the result again, it is very likely you > have to do quite a lot of queries before you get the result. > > So in other words, just lay out the data which makes the most sense to > you, the pain of recreating SQL like logic is there no matter what > layout you choose. > > -- > mph
Instead of creating a new table, just create an iterator that returns successive entries in it. Just don't change the size of either table during iteration. -- http://mail.python.org/mailman/listinfo/python-list
