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From "Emmanuel Venisse" <emmanuel.veni...@gmail.com>
Subject Re: Some continuum-jpa branch updates
Date Thu, 24 Jan 2008 09:04:23 GMT
On Jan 22, 2008 3:06 AM, Rahul Thakur <rahul.thakur.xdev3@gmail.com> wrote:

>
> A Query object that wraps up criteria and is built programmatically
> affords us the ability to keep Store APIs lean and stable. That is the
> motivation behind building up queries programatically. IMHO, the current
> ContinuumStore is a bunch of methods that don't even vary that much
> underneath. I think the same can be easily achieved by using Query.
>

With named queries, queries are cached in the persistence context so they
don't need to be parsed each time.
With named queries, an other good thing is that they can be overriden in the
xml file if needed for performance for a specific DB and we can add query
hints.
The last thing is that with named queries, we know exactly which requests we
execute so we can optimize the DB schema with some index, it isn't easy to
do with dynamic queries.

I don't say we won't use dynamic queries but only that it must be the
majority of our requests and it's a JPA best practices.


>
> I am not sure if StringBuilder will be more performant than StringBuffer
> when you are concatenating only a few Strings. I think what is more
> important is a goal of a lean, test'able and clean API.
>

It isn't important for a concatenation of few strings, but in your code, you
do it in the Query generator. The concatenation will executed a lot because
we execute lot of requests in all pages, so the benefit of StringBuilder is
very important.


>
> I can't really comment on named queries (probably need to toy around
> with them a bit), and not sure how the implementation would end up
> making use of named queries, but if anyone else has any opinions, I am
> keen to understand.
>
> Cheers,
> Rahul
>
> Emmanuel Venisse wrote:
> > As Christian said, named queries are pre-compiled to SQL. With dynamic
> > queries, perf can be not good because for each execution, the JPQL
> request
> > is recompile to SQL, so parsing, creation of the JPQL tree then SQL
> > generation, and with your solution, you concatenate lot of String. It
> isn't
> > important for one request but with lot of request, you use more time and
> > cpu, for string concatenation, it is better to use StringBuilder that is
> > more performant than String addition or StringBuffer.
> >
> > An other argument for named queries is that with dynamic queries, if
> they
> > aren't written correctly (it isn't the case for your code ;) ), it is
> easy
> > to introduce some malicious SQL code with parameters
> >
> > my two cents.
> > Emmanuel
> >
> > On Jan 18, 2008 9:57 PM, Christian Edward Gruber<cgruber@israfil.net>
> > wrote:
> >
> >
> >> You can get some benefit from named queries in terms of query pre-
> >> compilation and caching on the underlying database.  However, most
> >> database flavors and hibernate providers turn criteria queries into
> >> named queries (parameterized SQL) which is then cached, so, on the
> >> surface I suspect the performance characteristics will be similar.
> >>
> >> Christian.
> >>
> >> On 18-Jan-08, at 14:35 , Rahul Thakur wrote:
> >>
> >>
> >>> Thanks Emmanuel! Responses inlined...
> >>>
> >>> Emmanuel Venisse wrote:
> >>>
> >>>> Hi Rahul,
> >>>>
> >>>> After few days to look at JPA, I'm sure now it would be good to use
> >>>> it
> >>>> instead of the actual JDO/JPOX (I know JPOX 1.2 support JPA).
> >>>> The code is very easy to write and to read with JPA.
> >>>>
> >>>> About your continuum-jpa branch, I have few remarks:
> >>>> - I don't think it's good to use directly some OpenJPA APIs. If
> >>>> possible,
> >>>> I'd prefer to use only standard JPA APIs so we'll can choose later
> >>>> the
> >>>> implementation we want to use (OpenJPA, TopLink, JPOX...)
> >>>>
> >>>>
> >>> Agree. The only place where OpenJPA APIs are being used directly
> >>> currently are the unit tests.
> >>>
> >>>> - why do you use some Spring code?
> >>>>
> >>>>
> >>> Experimental. Spring has a good transaction management framework out
> >>> of the box.
> >>>
> >>>> - we don't need to store the model encoding
> >>>> (CommonUpdatableModelEntity
> >>>> class)
> >>>>
> >>>>
> >>> Sure. Easily fix'able. :-)
> >>>
> >>>> - can you explain dateCreated/dateUpdated fields? How are they
> >>>> managed?
> >>>>
> >>>>
> >>> These are for audit puposes, and can be used as range search query
> >>> criteria for fetching entities. These were an extension I thought
> >>> will be good. 'dateCreated' gets set when an entity is first
> >>> inserted into the underlying store, subsequent updates update the
> >>> 'dateUpdated'.
> >>>
> >>>> - all the model is fectched eagerly and it isn't acceptable for
> >>>> performance
> >>>>
> >>>>
> >>> Yes, the model does needs review and tweaks to annotations where we
> >>> know we don't need to fetch 'eagerly'.
> >>>
> >>>> - I'm not sure your Query "pattern" is good. I'd prefer to use
> >>>> named queries
> >>>> but maybe you have a reason
> >>>>
> >>>>
> >>> I think using a Query like we have on the JPA branch nicely provides
> >>> for a flexible construction of queries (i.e, only the criteria
> >>> passed in contributes to the query). I am not sure if such is
> >>> available with named queries; but I am interested to know why named
> >>> queries might be better.
> >>>
> >>> Cheers,
> >>> Rahul
> >>>
> >>>
> >>>> That's all for the moment.
> >>>>
> >>>> Emmanuel
> >>>>
> >>>> On Jan 16, 2008 11:30 PM, Rahul Thakur
> >>>> <rahul.thakur.xdev@gmail.com>  wrote:
> >>>>
> >>>>
> >>>>
> >>>>> Just wondering if anyone else got to the changes?
> >>>>>
> >>>>>
> >>>>> Emmanuel Venisse wrote:
> >>>>>
> >>>>>
> >>>>>> I don't have the time to look at it these days but I'll do it
asap
> >>>>>> (maybe in few weeks :( )
> >>>>>>
> >>>>>> Emmanuel
> >>>>>>
> >>>>>> Rahul Thakur a écrit :
> >>>>>>
> >>>>>>
> >>>>>>> Hi All,
> >>>>>>>
> >>>>>>> Scribbling some quick notes on some of the toying around
I have
> >>>>>>> been
> >>>>>>> doing with OpenJPA, Generics etc on the continuum-jpa branch[1]:
> >>>>>>>
> >>>>>>> 1) Use JPA for persistence
> >>>>>>> Motivation behind this has been to investigate how this
compares
> >>>>>>> to
> >>>>>>> JPOX/JDO for managing the model - both in terms on performance
and
> >>>>>>> ease of use (Store APIs). Continuum model classes are annotated
> >>>>>>> with
> >>>>>>> JPA annotations on the branch. However, this needs a review
as
> >>>>>>> there
> >>>>>>> are some elements (for example 'configuration' typed as
Map)
> >>>>>>> that I am
> >>>>>>> not sure yet how to persist yet. The provider used is OpenJPA
[2].
> >>>>>>>
> >>>>>>> 2) Refactorings to Store interface
> >>>>>>> Main motivation has been to keep the core Store interface
lean and
> >>>>>>> mean (read extensible). The Store interface[3] now has 4
methods:
> >>>>>>> lookup()
> >>>>>>> save()
> >>>>>>> delete()
> >>>>>>> query()
> >>>>>>>
> >>>>>>> The lookup(), save() and delete() act on single model Entity,
> >>>>>>> while
> >>>>>>> query() will filter and obtain matching Entities from the
> >>>>>>> underlying
> >>>>>>> database based on the Query specified. Query implementations
> >>>>>>> control
> >>>>>>> how a resulting JPQL gets constructed and which matching
> >>>>>>> entities get
> >>>>>>> pulled, and can be easily extended.
> >>>>>>>
> >>>>>>> To preserve compatibility with the existing Store interface,
we
> >>>>>>> can
> >>>>>>> mimick the existing ContinuumStore interface operations
by
> >>>>>>> having a
> >>>>>>> facade that can prepare requisite queries and delegate to
a Store
> >>>>>>> instance.
> >>>>>>>
> >>>>>>> 3) Misc.
> >>>>>>> There are a few I am investigating:
> >>>>>>> 1) Spring/Guice under the hood.
> >>>>>>> 2) JUnit 4.4 (and Hamcrest library)
> >>>>>>> , but these are still in early stages.
> >>>>>>>
> >>>>>>> I am keen to get a feedback on what others think.
> >>>>>>>
> >>>>>>> Cheers,
> >>>>>>>
> >>>>>>> Rahul
> >>>>>>>
> >>>>>>>
> >>>>>>> [1] -
> >>>>>>>
> >>>>>>>
> >> http://svn.apache.org/repos/asf/maven/continuum/branches/continuum-jpa/
> >>
> >>>>>>> [2] - http://openjpa.apache.org/
> >>>>>>>
> >>>>>>> [3] -
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>
> http://svn.apache.org/repos/asf/maven/continuum/branches/continuum-jpa/continuum-model-jpa/src/main/java/org/apache/maven/continuum/store/api/Store.java
> >>
> >>>>>>>
> >>>>
> >>
> >
> >
>
>

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