On 10 September 2013 19:28, Kevin Meyer - KMZ <[email protected]> wrote:
> > I would be interested in knowing if it is possible to use the DN meta > data API to allow the JDO data store to make intelligent guesses > (that'll generally be "right", or at least a default that is generally > useable). > Yes, I think that by and large that would be possible. Certainly, a lot of the Estatio entities are all very similar to each other. I could also imagine "profiles" whereby we map one way for a "typical" RDBMS setup, and a slightly different way to support Google App Engine. (Maurizio tells me off-list that this is working fine; he's in the middle of getting his committer perms sorted in order to do the necessary commit). > > Then, when the defaults are not good enough (some final deployment > tweaking would improve behaviour or performance), let the developer > provide JDO annotations as required. > > Yeah, I think that would be necessary. > Of course, some Isis annotations (e.g. @Optional) also impact on the > database (implicitly requiring "allowNulls = true") and there is possibly > no way around this (unless one of the defaults to the datastore is that > allowNulls is always true!) > > At the moment we have Isis recognizing @Column(allowsNull=true) to mean optional. But if we use the DN metadata API, then we could go the other way (ie use @Optional to setup the DN metamodel instead). So goal is to get the objectstore "working" as soon as possible with no > (or very few) data-store specific annotations on the POJOs. > > Very happy to support you on this Kevin. For myself, I shan't be putting any time into it; need to keep focussed on getting Estatio live. > So, the question is: Can the metadata API provide enough input to > DN that an introspector (using the Isis metamodel) can guess the > required DN metadata for entities and properties (single valued and > collections) if there are no annotations? > > To a large extent, yes. The main things we don't have are bidirectional relationships and inheritance mapping (roll-up vs table-per-type vs roll-down). For these I think we just recognize the JDO annotations. > I don't understand the relationship between JDO and DN, so I would > need to do a lot of research first.. ;) JDO is the API, DN is the implementation. (DN also supports the JPA API, so after we get this sorted out to our mutual satisfaction, we can go round the loop and look at JPA). > Perhaps a better understanding > would clarify why my goal is pointless (or impossible). > > It's doable. The question remains: do we expect our would-be users to learn the Isis conventions (and learn about its default mappings), or do we let them bring their existing JDO (and one day) JPA knowledge and then have Isis do "the right thing". Dan
