Hi Mike I've had some similar thoughts in the past myself.
Where I think this has most use is when some complex mapping is required thats specified declaratively in XML. eg. when you are navigating over beans, or XML or SQL and performing complex mappings, where you may set properties on JDO objects, invoke EJB methods, do some arbitrary SQL, invoke some web service(s) or output an XML view of your beans or whatever. e.g. in EAI or implement complex bindings of beans to web service calls or whatever. I've never quite considered mapping from data objects to JDO yet though. I'm interested in seeing how this pans out. James ------- http://radio.weblogs.com/0112098/ ----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Wednesday, November 27, 2002 1:18 PM Subject: [Jelly] Tags to create or transform an object graph Hi, Many people are using the DTO "pattern" in their webapps to transfer data back and forth between their persistence and presentation layers. For those who decide to adopt this pattern, they find themselves with two different object models: the persistence (domain) model which is mapped to an underlying data store and a Java Bean model that is used by the JSPs and Struts actions or what have you. The problem with this is that you find yourself writing a tonne of this kind of get()/set() code: domainObject.setName(beanObject.getName()); Additonally, if you are using some kind of O/R mapping runtime, you want to do a set() only if it required, to limit the number of SQL UPDATE statements, so you have code like this everywhere: if ( !(domainObject.getName().equals(beanObject.getName())) ) { domainObject.setName(beanObject.getName()); } I am half way through a set of Jelly tags that allow me succinctly describe the rules involved in this kind of situation. The above Java can be stated as <graph:set from="name" to="name"/> (assuming domainObject and beanObject are in the JellyContext and named as "target" and "source"). Sometimes more complex mappings are required: <graph:map name="person.site" sourceKeys="country.id,language.id" targetKeys="country.countryCode,language.languageCode"> <graph:change> <graph:lookup target="site" sourceKeys="country.id,language.id"/> </graph:change> <graph:prune objects="site"/> </graph:map> What this says is "if source.getCountry().getId() and source.getLanguage().getId() are different to target.getCountry().getCountryCode() and target.getLanguage().getLanguageCode() resp, then set target.site to the result of a lookup based on specified params. (lookup uses an ObjectManager.lookup() instance, available from the context). Alternatively, if either of the sourceKeys is missing or valueless, prune target.site". Now, I guess this is more likely to make sense if, like me, you are using JDO as your persistence runtime. This allows the graph mapper to surf references as it needs, driven by the Jelly script. But, what I wanted to know is is there a better way to do this, is somebody else working on something similar and, if not, whether you would consider sucking these tags into the Jelly dist and allow many minds to make them better ;-) Thanks a mil, Mike. PS I initially looked at using JXPath to do this, but that is good at pulling data out of a graph, but not so good at transforming a target graph based on the content of a source graph. Pruning is the biggest problem I see, but I am open to correction. -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]> __________________________________________________ Do You Yahoo!? Everything you'll ever need on one web page from News and Sport to Email and Music Charts http://uk.my.yahoo.com -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
