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From Niclas Hedhman <nic...@hedhman.org>
Subject Re: GeoSpatial Query support
Date Thu, 11 Jun 2015 09:29:18 GMT
Kent,
Nice to hear your refreshing input. Perhaps you have a very strong point.
Loooong ago, the Query and Storage was more intertwined (days before
org.qi4j.api.property.Property and we tried to do pojo-style "properties")
than it is today, and perhaps we stopped that separation "too early" and
even further modularization makes good sense. I am not sure...

But let me guess; People tend to forget how complex the "Module" is. The
"current module" is two parts, one that holds the module from where
UnitOfWork is created, and one "follows" the execution stack, i.e. just
before the invocation stack is invoked, a bunch of stuff is assigned to it,
including this handling of the "current module". Why? That is to make the
whole Visibility thing to work as expected. In the early days, we had a lot
of "bugs" (unexpected behavior) due to this...

I am guessing that a QueryBuilder @Service would have problem with the same
thing, i.e. it can handle the Entity type that is being requested, but any
dereferencing of associations might cause problems. As I said above, I am
not sure, but willing to investigate it.


Regarding your examples;
SpecificationQueryBuilder<Person> sqb =
this.module.newQueryBuilder( SpecificationQueryBuilder.class,
Person.class );

here you still have "this.module" but in the text I get the impression that
you even consider a totally stand-alone @Service QueryBuilderFactory
(instead of the @Structure one), with regular injection.


Cheers

On Thu, Jun 11, 2015 at 3:20 PM, Kent SĂžlvsten <kent.soelvsten@gmail.com>
wrote:

> While I agree that the goal of decoupling the query part from core is a
> worthy one, I fail to see what UnitOfWorkFactory has to do with that.
>
> Decoupling the UnitOfWork may or may not make sence, but I think that is
> another discussion - which could make sense eg. if you wish to integrate
> a Zest application with an XA transaction manager.
>
> Since the EntityFinders are responsible for executing a Query it makes
> since to me to let the EntityFinder be involved in creating the query.
> So a possible design could be to simply break out the querybuilder API's
> form core. No more, no less.
>
> Let us say that the core API only consists of
>
> public interface QueryBuilder<T> {
>   Query<T> newQuery( UnitOfWork uoq );
> }
>
> public interface QueryBuilderFactory {
>     <QB,T> QB<T> newQueryBuilder( Class<QB extends QueryBuilder>
> builderType, Class<T> resultType )
>         throws MissingIndexingSystemException,
> InvalidQueryLanguageException;
> }
>
> Query interface still in core, looking as of today.
>
> QueryBuilderFactory should no longer be embedded inside the module, but
> instead be a service (probably implemented by the extension that also
> implements the EntityFinder).
>
> Concrete QueryBuilder interfaces/impls and Query implementations are
> moved to libraries (one library implementing SpecificationQueryBuilder,
> another implementing SparQLQueryBuilder ....)
>
> Application code could then be something like:
>
>         SpecificationQueryBuilder<Person> sqb =
> this.module.newQueryBuilder( SpecificationQueryBuilder.class,
> Person.class ); // h
>         Property<String> nameProp = templateFor( Person.class ).name();
>         sqb = sqb.where( eq( nameProp, "Kent") );
>         Query<Person> query = unitOfWork.newQuery( qb );
>
> or
>         SqlQueryBuilder<Person> sql = this.module.newQueryBuilder(
> SqlQueryBuilder.class, Person.class );
>         sql = sql.where( "name = 'Kent'");
>         Query<Person> query = sql.newQuery( unitOfWork );  // this
> QueryBuilder might have a special query implementation
> or
>         SesameQueryBuilder<Person> sesame = this.module.newQueryBuilder(
> SesameQueryBuilder.class, Person.class );
>         sesame = sesame.bySparql( queryString);  // this queryBuilder is
> now probably immutable
>         Query<Person> query = sesame.newQuery( unitOfWork );  // this
> QueryBuilder might have a special query implementation
>
>
> Some of the QueryBuilder libraries might only consist of an API
> (implementations supplied by the extension also supplying the
> EntityFinder) - other libraries might have a default implementation to
> facilitate several entitystores supporting that Query 'language'.
> Note that some EntityFinders  might support several Query 'languages',
> both a specification based and a native one.
>
> We might even some day be able to support JPA or Hibernate, allowing the
> user to create a Zest app combining existing data in a relational
> database with geospatial data? (that would probably require some
> re-thinking of the UnitOfWork concept).
>
> Am I making sense?
>
> /Kent
>
>
>
>
>
>
>
>
> Den 06-06-2015 kl. 05:41 skrev Niclas Hedhman:
> > Thanks Martin, that gives a nice overview of the situation (you should
> > plaster that on frontpage)...
> >
> > Zest gang,
> > So, I think our challenge is to be able to introduce Geospatial
> > indexing/querying, without introducing a dependency.
> >
> > What do I mean by this?
> >
> > Well, we already have another "Custom Query" type, the Lucene free-text
> > search, which couldn't be fitted nicely into the very nature of the
> > UnitOfWork/QueryExpressions/QueryBuilder system.
> >
> > So let's hypothesize about;
> >   * Ability to introduce new indexable data types,
> >   * Ability to introduce extensions to the Query DSL
> >   * Ability to extend the Indexing/Query extension itself.
> >
> >
> > Where is the root of this system? Well, it all begins in the UnitOfWork.
> > So, one possibility would be to disconnect UnitOfWorkFactory from the
> > Module itself, and have a ServiceComposite for the UnitOfWorkFactory.
> Once
> > the UnifOfWorkFactory implementation is outside the Core Runtime, so is
> > UnitOfWork and everything that derives from it. It SHOULD mean that all
> > parts could be Composites, in which case we can add arbitrary methods to
> > them, the static methods of QueryExpressions could go away and probably
> > other, yet to be discovered, benefits.
> >
> > Granted, it won't be common for users to create their own, but having
> this
> > possibility, without becoming incompatible and without introducing
> > dependencies in the Core, seems to me to be worthwhile going down this
> > route. Having such a major part of the Core to be on the "Composite-side
> of
> > things", might open up more cool ideas...
> > It also feels "right" along our habit of breaking things out of Core and
> > moving towards more modularity.
> >
> > On paper, it sounds reasonably easy to do this, but I bet the devil is in
> > the details. Maybe an impossible circular dependency will arise, or
> > something to that extent.
> >
> >
> > Any thought on this?
> >
> >
> > Cheers
> >
> > On Fri, Jun 5, 2015 at 4:57 PM, Martin Desruisseaux <
> > martin.desruisseaux@geomatys.com> wrote:
> >
> >> Thanks Chris for getting Zest and SIS in touch. I just finished reading
> >> the thread. There is some tips for information purpose:
> >>
> >> Niclas Hedhman wrote:
> >>
> >>> So, IF SIS are primarily based around interfaces, then that would be
> >>> great and we can possibly leverage quite a bit, especially at what we
> >>> call "Library" level, i.e. not part of the Core runtime itself, which
> >>> we try to keep free of dependencies
> >> The core part of SIS is defined by a set of interfaces provided by a
> >> separated project: http://www.geoapi.org/. GeoAPI consists of only
> >> interfaces, except some classes for Exception, Enum and "CodeList"
> >> (similar to Enum but extensible). GeoAPI is based on some international
> >> standards published jointly by the Open Geospatial Consortium (OGC) and
> >> International Organization for Standardization (ISO). It currently
> >> covers only a small part of OGC standards, but this includes map
> >> projections.
> >>
> >> Apache SIS is a GeoAPI 3.0 implementation. The GeoAPI project provides
> >> also implementations as wrappers around Proj.4 (the C/C++ library used
> >> by GDAL) and the UCAR NetCDF library. All those projects have advantages
> >> and inconvenient (e.g. Proj.4 supports a wider range of map projections
> >> than SIS, but SIS is more compliant with OGC/ISO standards). But if Zest
> >> depends directly on only GeoAPI interfaces you would have the freedom to
> >> change implementation. However I do not know if Spatial4J would be
> >> interested to implement GeoAPI interfaces.
> >>
> >> On geometry and indexing, there is no satisfying solution on GeoAPI side
> >> yet. In particular, geometries are defined by the ISO 19107
> >> international standard, which is currently under revision. This will
> >> have a deep impact on GeoAPI once the ISO revision will be completed.
> >>
> >> Please let us know if you would like to explore further (e.g. how to
> >> apply a map projection using the API defined by GeoAPI).
> >>
> >>     Martin
> >>
> >>
> >
>
>


-- 
Niclas Hedhman, Software Developer
http://zest.apache.org - New Energy for Java

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