It may be irrelevant, but I have been playing recently with OmniBase, which is a fully object-oriented database system, now over 20 years old, but it still works very well for my uses. David Gorišek, the author, claims that it has ACID properties. From my reading, updates operate on a proxy object, which is not written to the database until an explicit commit is given. A second transaction accessing the same object will still see the original until the change is committed. What happens to a proxy which is never committed is not clear, but if Gorišek is right, the stored data can never be contaminated. I think a proxy in this sense is equivalent to a memento.
Thanks to Esteban Lorenzano, OmniBase is now available on Pharo. The code is ancient, there is no documentation and obviously no support, but it might be worth while for someone to try some software archaeology and put it to use. I have found it possible to create and maintain a small database of natural language information, and access is fairly quick and easy – and it’s all Smalltalk. It claims to store all kinds of Smalltalk objects, except block closures, and skimming through the code it seems to incorporate a serializer similar to Fuel. The only documentation I have found is a slideshow at https://www.slideshare.net/esug/omni-baseobjectdatabase. I have found out a few things about it, if anyone is interested. Peter Kenny From: Pharo-users <pharo-users-boun...@lists.pharo.org> On Behalf Of Norbert Hartl Sent: 09 October 2019 18:08 To: Any question about pharo is welcome <pharo-users@lists.pharo.org> Subject: Re: [Pharo-users] voyage mongo and transactionality Am 09.10.2019 um 16:48 schrieb "jtuc...@objektfabrik.de <mailto:jtuc...@objektfabrik.de> " <jtuc...@objektfabrik.de <mailto:jtuc...@objektfabrik.de> >: This is a tricky mine field. Sometimes you need a lot of business functionality in objects referenced in your objects that are currently in the editor. So I'm still to see a project in which the memento pattern really worked for more complex scenarios. How deep do you dive to have enough memento objects to provide the functionality needed. I guess you can do that with some sort of object-level transaction framework that automatically creates mementos of whatever object is being navigated to during some kind of processing-context. I guess slots could be of use here. But this is not trivial for general cases. Yes it is tricky. You can have copies of business objects but you have always references to the business objects not pointing to the copy. And you need to know which objects should be tracked. In Gemstone IIRC it is easy as it is the time the object is copied from the stone to the gem it is registered in the current transaction. So you can check it and committing if it changed because you have to write it back. The important point here might be get noticed when a reference is acquired. In pharo it is not that easy but could be done if object would be reified and interceptable. In my experience, this problem area makes for the other 70% of the time spent on developing GUI or Web applications, besides the 60% for GUI design and implementation and 25% business logic... 70% + 60% + 25% + 30% = 185% sounds indeed very realistic if it comes to project planning. 😛There is even a rule saying that for the first 90% of the project you need the first 90% of time and for the last 10% of the project you need the second 90% of time. I'd be interested to learn about patterns to handle such more complex things. We constantly travel back and forth between implementing stuff in the GUI handlers (copying values to the GUI classes that access themselves during GUI operations and push values to the business objects when the users clicks on OK), using mementos (which most of the times are nets of mementos that are created manually - "we know what we'll touch in this Editor") and operating on business objects directly and relying on the persistence mechanism (Glorp in our case) and its rollback behaviour. All three have lots of weaknesses and seem to have their place nevertheless. So this is a very interesting discussion and I think this is an area that has not been solved yet. I think it isn‘t solved and I find every piece of information about it very interesting. Norbert Joachim Am 09.10.19 um 16:25 schrieb James Foster: Thanks for the explanation. And, yes, this is an artifact of your design; if you put intermediate values into domain objects then they will remain in your domain objects to be seen later. From what you’ve described, I don’t see how it would be any different in a non-image environment (Java, C#, etc.), unless you re-read the entire object graph from the database. As someone else mentioned, this would be a good place for the Memento Pattern. James On Oct 9, 2019, at 1:59 AM, Jonathan van Alteren <jvalte...@objectguild.com <mailto:jvalte...@objectguild.com> > wrote: Hi James, I see how my explanation might be unclear. We have a main form for the agenda and a subform for an item, which is shown using Seaside call/answer. The save button of the subform is clicked, which adds the item to the underlying agenda model object, but the save button of the main form is not clicked by the user. The callback for the main save button sends the save message to the agenda object, causing the database to be updated. So yes, the browser does submit the data on the subform, it's the main form component that doesn't receive the save button callback. I realize that this is in large part an issue with our design. However, the way object persistence seems to work in the image environment plays a large role. Kind regards, Jonathan van Alteren Founding Member | Object Guild jvalte...@objectguild.com <mailto:jvalte...@objectguild.com> On 8 Oct 2019, 15:41 +0200, James Foster <smallt...@jgfoster.net <mailto:smallt...@jgfoster.net> >, wrote: On Oct 8, 2019, at 3:05 AM, Jonathan van Alteren <jvalte...@objectguild.com <mailto:jvalte...@objectguild.com> > wrote: We've encountered an issue where a user makes changes to an agenda, but does not click the Save button. Instead, the user closes the browser or uses the navigation to go to a different part of the application. When navigating back to the original agenda, the changes made previously (e.g. items added) are still being displayed, even though they were never explicitly saved. Here is what I don’t understand: how did the change get from the user’s client agent (browser) to the server? If you make a change to a field in a form and then close the browser, who sent the change to the server? If you show the save domain value in a different location, with a dynamically-generated id and name (so it isn’t cached in the browser), or written to the Pharo Transcript, does the value still change? That is, are you sure that the change is in the reflected in the Smalltalk image and not just somehow cached in the browser? James -- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuc...@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1
