Hi Peter, I will submit the code to my Github repo later today and will document it with an example on my Github wiki.
The mechanism to extend existing classes (using implicit conversations) only works from within Scala, so the code I wrote is not usable within a Java project. Kind regards, Niels Hoogeveen > From: neubauer.pe...@gmail.com > Date: Fri, 26 Mar 2010 17:25:01 +0100 > To: user@lists.neo4j.org > Subject: Re: [Neo] meta meta classes > > Awesome Niels! > > maybe you could blog or document some cool example on this? > > Cheers, > > /peter neubauer > > COO and Sales, Neo Technology > > GTalk: neubauer.peter > Skype peter.neubauer > Phone +46 704 106975 > LinkedIn http://www.linkedin.com/in/neubauer > Twitter http://twitter.com/peterneubauer > > http://www.neo4j.org - Your high performance graph database. > http://www.tinkerpop.com - Processing for Internet-scale graphs. > http://www.thoughtmade.com - Scandinavias coolest Bring-a-Thing party. > > > > On Fri, Mar 26, 2010 at 5:22 PM, Niels Hoogeveen > <pd_aficion...@hotmail.com> wrote: > > > > Using Scala, I was actually able to extend MetaModelThing to act as a Node > > and MetaModelClass to have shadowing functionality for both > > MetaModelClasses and for MetaModelProperties, without touching the original > > source code. > > > >> To: user@lists.neo4j.org > >> From: rick.bullo...@burningskysoftware.com > >> Date: Fri, 26 Mar 2010 14:29:03 +0000 > >> Subject: Re: [Neo] meta meta classes > >> > >> Such are the joys and challenges of frameworks and abstractions. > >> Sometimes you do need to get "close to the metal" though, to achieve > >> specific functional and performance requirements. Thus the reason open > >> source frameworks are awesome. At least we can change and extend them > >> more easily! > >> > >> > >> > >> -----Original Message----- > >> From: Niels Hoogeveen <pd_aficion...@hotmail.com> > >> Date: Fri, 26 Mar 2010 15:20:15 > >> To: <user@lists.neo4j.org> > >> Subject: Re: [Neo] meta meta classes > >> > >> > >> Making MetaModelThing implement the Node interface is actually orthogonal > >> to the creation of Shadow objects. Though it does make code using classes > >> as objects cleaner, and allows the node property of MetaModelThing to > >> become private. > >> > >> > From: pd_aficion...@hotmail.com > >> > To: user@lists.neo4j.org > >> > Date: Fri, 26 Mar 2010 14:38:08 +0100 > >> > Subject: Re: [Neo] meta meta classes > >> > > >> > > >> > Or, and this probably the simplest solution. Let a MetaModelThing > >> > implement the Node interface. This allows a class to be an instance of > >> > another class and/or a SubType of another class. > >> > > >> > > >> > > From: pd_aficion...@hotmail.com > >> > > To: user@lists.neo4j.org > >> > > Date: Fri, 26 Mar 2010 14:20:07 +0100 > >> > > Subject: Re: [Neo] meta meta classes > >> > > > >> > > > >> > > The class as object phenomenon is actually quite pervasive, and I > >> > > think it is possible to have a generalized solution for it. > >> > > > >> > > After sending this email yesterday, I came up with a slightly > >> > > different solution. > >> > > > >> > > val taggable = namespace.getMetaClass("taggable", true) > >> > > > >> > > val tagName = metaModelNamespace.getMetaProperty("tagname", true) > >> > > tagName.setCardinality(1) > >> > > > >> > > val metaTaggable = metaModelNamespace.getMetaClass("taggable", true) > >> > > metaTaggable.getDirectProperties.add(tagName) > >> > > metaTaggable.getDirectInstances.add(taggable.node) > >> > > > >> > > val body = namespace.getMetaClass("body", true) > >> > > taggable.getDirectSubs.add(body) > >> > > > >> > > Instead of directly relating the class "body" to the meta class > >> > > "taggable", I create a shadow of the meta class "taggable" with the > >> > > same name in the namespace of the class "body", and make "body" a > >> > > subclass of this shadow. That way the sub classing relationship > >> > > remains nicely in one name space, while the instance relationship > >> > > transcends name spaces, as it should. > >> > > > >> > > This could in principle be generalized by adding a methods to > >> > > MetaModelClass: > >> > > > >> > > public MetaModelClass createShadowClass(NameSpace ns){ > >> > > > >> > > MetaModelClass mc = ns.getMetaClass(this.getName(), true); > >> > > this.getDirectInstances.add(mc.node); > >> > > return mc; > >> > > } > >> > > > >> > > This returns a shadow of a given MetaModelClass in a given namespace > >> > > and adds it as a an instance of this. > >> > > > >> > > It would of course be nicer to have a method with the signature: > >> > > > >> > > public MetaModelClass getShadow(NameSpace ns, Boolean create) > >> > > > >> > > This is much more in line with the rest of the API, but requires a way > >> > > to find out the namespace a given MetaModelClass is defined in. I > >> > > didn't see a method getNamespace() for a given class, and didn't delve > >> > > deeply enough in the source code to figure out how to do that. > >> > > > >> > > A similar approach can of course also be applied to > >> > > MetaModelProperties, by adding the following method to MetaModelClass: > >> > > > >> > > public MetaModelProperty > >> > > createShadowProperty(NameSpace ns){ > >> > > > >> > > > >> > > > >> > > MetaModelProperty mp = > >> > > ns.getMetaProperty(this.getName(), true); > >> > > > >> > > > >> > > this.getDirectInstances.add(mp.node); > >> > > > >> > > return mp; > >> > > > >> > > } > >> > > > >> > > > >> > > This way the underlying node of a MetaModelProperty can properly be > >> > > used as a class of its own and have properties, relationships, that > >> > > can be further modeled in the meta layer. This e.q. allows to set a > >> > > default rendering format for a given property class. > >> > > > >> > > I don't see a MetaModelRelationships, which is unfortunate, since that > >> > > would allow the modeling of the properties of a Relationship. > >> > > > >> > > > >> > > Kind regards, > >> > > Niels Hoogeveen > >> > > > >> > > > >> > > > Date: Fri, 26 Mar 2010 11:26:29 +0100 > >> > > > From: matt...@neotechnology.com > >> > > > To: user@lists.neo4j.org > >> > > > Subject: Re: [Neo] meta meta classes > >> > > > > >> > > > That's an interresting case you've got here and it looks to me like > >> > > > it's > >> > > > probably the best way to model it in the meta model. > >> > > > > >> > > > 2010/3/25 Niels Hoogeveen <pd_aficion...@hotmail.com> > >> > > > > >> > > > > > >> > > > > For my application, I want to model an HTML template in Neo4J, > >> > > > > using the > >> > > > > MetaModel api. > >> > > > > > >> > > > > So I started setting up MetaModelClasses for the various HTML > >> > > > > entities. > >> > > > > > >> > > > > e.g. (code in Scala) > >> > > > > > >> > > > > val classProp = namespace.getMetaProperty("class", true) > >> > > > > val idProp = > >> > > > > namespace.getMetaProperty("id", true) > >> > > > > idProp.setCardinality(1) > >> > > > > > >> > > > > > >> > > > > val body = namespace.getMetaClass("body", true) > >> > > > > body.getDirectProperties(classProp) > >> > > > > body.getDirectProperties(idProp) > >> > > > > > >> > > > > > >> > > > > Which creates a class named "body" which has a property named > >> > > > > "class" > >> > > > > without a cardinality restriction and a property named "id" with a > >> > > > > cardinality restriction of 1. > >> > > > > > >> > > > > Now I can create nodes of class "body" with various values for > >> > > > > "class" and > >> > > > > for "id". > >> > > > > > >> > > > > So far so good, but now I want to say that the class body has a > >> > > > > property > >> > > > > "tagname" which should get the value "body". > >> > > > > > >> > > > > The meta model itself doesn't allow classes to have properties, > >> > > > > but it > >> > > > > allows access to the underlying node of the class. > >> > > > > > >> > > > > So I created a separate namespace for the meta meta classes and > >> > > > > added the > >> > > > > following three definitions: > >> > > > > > >> > > > > val tagName = metaNamespace.getMetaProperty("tagname", true) > >> > > > > tagName.setCardinality(1) > >> > > > > val taggable = metaNamespace.getMetaClass("taggable", true) > >> > > > > > >> > > > > body.node.setProperty("tagname", "body") > >> > > > > > >> > > > > This creates a property "tagname" with the value "body" for the > >> > > > > class named > >> > > > > "body". > >> > > > > > >> > > > > Now comes the more ambiguous part, how to link "body" to > >> > > > > "taggable". > >> > > > > > >> > > > > I can make body.node an instance of taggable. Once there is a > >> > > > > validator, > >> > > > > the existence of a "tagname" property with cardinality 1 should be > >> > > > > checked, > >> > > > > so it is reasonable to make body.node an instance of taggable. > >> > > > > > >> > > > > At the same time the class body is actually a subclass of > >> > > > > taggable, so I am > >> > > > > inclined to define that as well. > >> > > > > > >> > > > > So I end up doing the following: > >> > > > > > >> > > > > taggable.getDirectInstances.add(body.node) > >> > > > > taggable.getDirectSubs.add(body) > >> > > > > > >> > > > > I would like to know if this is the correct approach to this > >> > > > > situation, or > >> > > > > whether there are better alternatives. > >> > > > > > >> > > > > Kind regards, > >> > > > > Niels Hoogeveen > >> > > > > > >> > > > > > >> > > > > _________________________________________________________________ > >> > > > > New Windows 7: Find the right PC for you. Learn more. > >> > > > > http://windows.microsoft.com/shop > >> > > > > _______________________________________________ > >> > > > > Neo mailing list > >> > > > > User@lists.neo4j.org > >> > > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > > > >> > > > > >> > > > > >> > > > > >> > > > -- > >> > > > Mattias Persson, [matt...@neotechnology.com] > >> > > > Neo Technology, www.neotechnology.com > >> > > > _______________________________________________ > >> > > > Neo mailing list > >> > > > User@lists.neo4j.org > >> > > > https://lists.neo4j.org/mailman/listinfo/user > >> > > > >> > > _________________________________________________________________ > >> > > Express yourself instantly with MSN Messenger! Download today it's > >> > > FREE! > >> > > http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ > >> > > _______________________________________________ > >> > > Neo mailing list > >> > > User@lists.neo4j.org > >> > > https://lists.neo4j.org/mailman/listinfo/user > >> > > >> > _________________________________________________________________ > >> > New Windows 7: Find the right PC for you. Learn more. > >> > http://windows.microsoft.com/shop > >> > _______________________________________________ > >> > Neo mailing list > >> > User@lists.neo4j.org > >> > https://lists.neo4j.org/mailman/listinfo/user > >> > >> _________________________________________________________________ > >> New Windows 7: Find the right PC for you. Learn more. > >> http://windows.microsoft.com/shop > >> _______________________________________________ > >> Neo mailing list > >> User@lists.neo4j.org > >> https://lists.neo4j.org/mailman/listinfo/user > >> _______________________________________________ > >> Neo mailing list > >> User@lists.neo4j.org > >> https://lists.neo4j.org/mailman/listinfo/user > > > > _________________________________________________________________ > > New Windows 7: Find the right PC for you. Learn more. > > http://windows.microsoft.com/shop > > _______________________________________________ > > Neo mailing list > > User@lists.neo4j.org > > https://lists.neo4j.org/mailman/listinfo/user > > > _______________________________________________ > Neo mailing list > User@lists.neo4j.org > https://lists.neo4j.org/mailman/listinfo/user _________________________________________________________________ New Windows 7: Find the right PC for you. 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