Re: [xwiki-devs] Thoughts on new model proposal

Hi Caleb, Thanks for taking the time to provide this feedback! See below. On Sep 27, 2012, at 9:52 AM, Caleb James DeLisle &lt;calebdelisle(a)lavabit.com&gt; wrote: Right now it's a String. I don't recall why I proposed String rather than UUID, maybe to allow for changing the implementation in the future. I don't agree with this. MVC has nothing to do here. In MVC, the M stands for Model and this is the only thing we're talking about here. V (for View) and C (for Controller) are outside of the scope. What you hint at (I think) is a Layered Architecture and this we're going to do, by having the persistence layer in a different layer. However business objects are completely ok to call the persistence layer. My idea is to use a Rich data model (as the current model BTW), i.e. business operations are *in* the model object interfaces. This is where we need to agree. I personally don't want to use an Anemic model where you have business objects be just data holders (ie. only getters/setters) and move all business operations into a service layer. For more on this topic: * http://en.wikipedia.org/wiki/Anemic_domain_model (lists pros and cons) * http://www.martinfowler.com/bliki/AnemicDomainModel.html That's the reason for the Iterator: EntityIterator<Entity> getChildren(EntityType type) With an Iterator the implementation can do things like: * get a single item at a time from the DB * get a bunch of N items at once (in one request) from the DB Now you have a valid point that we may also want to have the ability to get children references. It's a good question. Now if we imagine that parents are stored as RDBMS column in a document table. Getting all children documents will mean doing a select in the document table where parent = a given parent ref ("select parent from document doc where doc.parent = ?"). Now getting getChildren() would do: select * from document doc where doc.parent = ?. The extra cost would just be the loading of marshalling/unmarshalling of data (which you would need thereafter in your logic). But I agree and it's possible that on other stores, it could cost less to get references. So I'd propose to have 2 methods: one for getting only children references and one for getting all children entities. There's no global variable. It's a thread local variable (i.e. visible only for the current thread). Yes I'd like to continue this. We didn't have it before in oldcore and XWikiContext was passed around everywhere which is why we moved to ThreadLocal. oldcore doesn't use this since it uses XWikiContext and not the Execution Context. Maybe you could explain in more details what you mean by "lot of inter-modular communication"? This has been discussed and voted on another thread so these names will be modified to match the result of that vote. Yes that's possible. However there could other methods such as a method to get the property definition. The user who started the session. Then set the store to use when you start the session. Yep, that was exactly the reason for the attributes parameter ;) We can tune this API and remove comment/minorEdit if we want. I'm not sure about putting them in Document; it's strange from an API POV IMO. I wouldn't want to use such as API where you have to remember to set the comment in the Document before calling save... Don't agree, see above. Nothing to do with MVC IMO. See above, anemic vs rich model. A Session is form a user POV. Technically it will use a Transaction but that's a technical implementation and it's more than that. It contains a user; it can contain the store to use, etc. Saving a Session means saving all entities that have been modified and have not been saved so far. This is the same as JCR (a lot of stuff come from JCR btw): http://www.day.com/maven/javax.jcr/javadocs/jcr-2.0/javax/jcr/Session.html Note that JCR 2.0 has deprecated Item.save() and I've researched this a bit but couldn't find the reason beyond "they wanted to simplify the API" and it's causing problems to users who want to just persist a given Item and what's below and the not the whole Session. Which is why I've kept having Entities implement Persistable so far. I prefer the current API: Entity parent = …; Space newSpace = parent.addSpace("child space"); Document newDocument = newSpace.addDocument("a document"); newDocument.setContent("This is content"); // Save the new entities created below parent parent.save(…); // Note: if we wanted to save all entities modified(not just the one in this tree) we would write: session.save(…); Your solution doesn't hide the implementation (DefaultSpace() and DefaultDocument() in this case) and makes it a lot harder to unit test. We don't want to repeat the issue we have today with unit testing XWiki/XWikiDocument... Good question. I don't know yet. A possibility is to pass the user in the save() call. Another is to use the Entity's author. Note that we also need a new User module anyway. Thanks -Vincent