On Wed, 2011-02-09 at 12:24 +1100, Scott Ritchie wrote: > Having looked at both, they seem fairly similar in terms of notation > and what we're trying to achieve. The only downside i can see to JPA > is it doesnt support Many-Many relationships, whereas JPO does > (allowing us to cut out UserTeamRelation if we want).
Aye. I had a bit of a closer look around last night and did some research. JDO is the older standard that was donated to the Apache project by Sun. It seems to be a little better suited for App Engine since it's not constrained to using a RDBMS (it can use a variety of stores). JPA is the newer standard and there are some politics behind it's formation (Certain RDBMS providers didn't like the idea of being completely decoupled from their systems?). Systems like Hibernate have a JPA provider in addition to their own built in API. App Engine uses DataNucleus provider that allows both JPA and JDO on App Engine but there are some limitations due to the underlying data store not being a RDBMS (See http://code.google.com/appengine/docs/java/datastore/jpa/overview.html#Unsupported_Features_of_JPA ). I'd be surprised if JPA can't do Many-Many in some form (even if it is deconstructed to a pair of 1-Many). Here seems to be a reasonable good overview of how you map classes with JDO - http://www.datanucleus.org/products/accessplatform/jdo/class_mapping.html . There's also an equivalent guide for JPA. Some more general links: http://www.datanucleus.org/products/accessplatform/jdo_jpa_faq.html http://db.apache.org/jdo/jdo_v_jpa.html http://stackoverflow.com/search?q=JDO+JPA Cheers, David
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