On 17 Apr 2014, at 15:18, Norbert Hartl <norb...@hartl.name> wrote: > > Am 17.04.2014 um 15:05 schrieb olivier auverlot <olivier.auver...@gmail.com>: > >> thanks Robert for the explications. >> > It’s Norbert btw. :) > >> I agree with you that's the best way to remove a book is to delete the >> reference in ComicsCollection. >> >> But how to do that ? Must I simply remove the reference in the ordered >> collection ? Voyage will syncronize automatically the data in memory with >> the content of the database ? Must I force the save of the data after >> removing the reference ? >> > You need to explicitly save it as we don’t have something like write barriers > in the image. So > > aComicCollection > removeBook: aBook; > save > > is needed.
yes, and also (if you want to be clean): aBook remove. (assuming aBook is also persistent). But as Sabina points: #enableMissingContent in CommicCollection will help you to simplify things, then you just need: "aBook remove", and next time you read aComicCollection it will “clean” the invalid reference. I call that “eventual integrity” :P but beware of it… is considered “power voyage programming” :) Esteban > > Norbert > >> Olivier ;-) >> >> >> 2014-04-17 14:10 GMT+02:00 Norbert Hartl <norb...@hartl.name>: >> >> Am 17.04.2014 um 13:53 schrieb olivier <olivier.auver...@gmail.com>: >> >> > Hi, >> > >> > I'm using Voyage in a Pharo application. >> > >> > I have two MongoDB collections which are ComicsCollection and ComicsBook. >> > Each book is attached to a instance of ComicsCollection. The reference of >> > each book is stored in an ordered collection (in the instance of >> > ComicsCollection). The problem is that if I remove a book, the reference >> > to the book is not deleted from ComicsCollection. >> > >> > How can I remove properly a book and the reference to the book ? >> > >> From the smalltalk image view the problem is usually exactly the opposite: >> You don’t delete objects but you remove references to them. As voyage maps >> objects it is a good idea to stay in the object realm. So you should rather >> remove the book from the collection. This way you won’t get errors just >> garbage. The „real“ problem that arises then is that the book would still be >> in the database. Just like it is in the image but there is no garbage >> collector for mongo. To decide that from the image is not possible. You load >> only a sub graph from the database into image memory. So you don’t know if >> there are other objects referencing the book. >> >> If your records fit all in memory you could load all collections and books >> and build the difference between all referenced books in the collections and >> the total amount of books. The difference will be the set of objects not >> being referenced by a collection and those can be deleted. >> >> If the records do not fit in memory an alternative strategy would be needed. >> I started to research if it is possible to build a map/reduce based garbage >> collector for common cases but got distracted. But I have the same problem >> so I will need to pick it up some time. >> >> hope that helps, >> >> Norbert >> >> >> >
