5 Apr
2011
5 Apr
'11
7:17 p.m.
Again this is sort of scaring discussion to me.
For minimal benefits - and there is still no persuasive example around -
you want to sacrifice proven (to avoid the word 'standard') query
language implementations to provide an own 'exotic' implementation ?
This doesn't make any sense to me except that it might be more fun to
write such an implementation
as to fix all outstanding JIRA issues.
Hibernate HQL is documented on ~30 printed pages with quite some examples:
http://docs.jboss.org/hibernate/core/3.3/reference/en/html/queryhql.html
The HQL chapter in Gavin King and Christian Bauers 'standard' 'Java
Persistence' book is about 50 pages long.
Both documentations sort of scratch the surface - they are still lacking
when it comes to writing real complex stuff.
aggregations / joins all the like ...
So - now you propagate a new QL. Maybe it is better - who knows ?
It's not useful if there is just a basic documentation.
Even with a very good documentation it needs to be learned and understood.
From the users point of view it would be more beneficial to focus
efforts on making XWiki more concise.
Just as an example this issue
http://jira.xwiki.org/jira/browse/XRENDERING-75
seems to be open since 2 years ...
Again I don't mean to criticize. But from time to time please try to see
your work through users glasses ...
regards
Andreas
Am 04.04.2011 16:37, schrieb Caleb James DeLisle:
On 04/04/2011 10:01 AM, Sergiu Dumitriu wrote:
On 04/02/2011 02:22 PM, Caleb James DeLisle
wrote:
The problem
now is we don't have any specification to tell us what is valid and what is not.
Is this a valid XWQL query?
$services.query.xwql("from BaseObject as obj where doc.fullName = obj.name and
obj.className =
'XWiki.XWikiUsers'").execute()
Run it and you might be surprised.
Based on that, we have no way of ensuring that a query which works now will work in a new
XWQL
implementation which defeats the purpose of abstracting the user away from HQL.
After searching through documentation on JPQL
(JPA's query language) I was unable to find any
example of the "doc.object(XWiki.XWikiUsers)" construct. This means XWQL is
it's own standard and
there is no authoritative reference on it. What makes an implementation compliant? I have
found that
most HQL queries can be executed as XWQL queries with little or no modification so if
compliance is
defined as being "just like the reference implementation" then nearly all HQL
must be implemented in
order to be compliant.
The goal of XWQL was to not be bound to a certain query
language, but to
be able to map it to as many QLs as possible, be they SQL-related, like
HQL or JPQL, or other types of queries, like QBE, XPath, SPARQL. So, it
wasn't meant from the start to be compatible with any standard. Now, I'm not sure if the right thing to do is
to move to a standard
query language, or to stick with our own.
If we're going to define our own
query language (I think there are enough already) there are certain
things we have to do such as writing a specification. I frankly find this thing
embarrassing.
- Is there any tool that allows mapping a JPQL or
JDOQL query into other
query languages?
http://www.datanucleus.org/products/accessplatform_3_0/datastores.html
These folks are mapping JDOQL and JPQL into a whole bunch of different types of storage.
- Is there a way to parse a query into a
tree/AST?
- Other than the fact that it's a non-standard language (and all the
consequences of this, like no support from tools and libraries), are
there any downsides to having our own query language?
This particular one has 2
downsides:
1. There is no official specification.
2. HQL can be run as shown above.
The major downside of implementing one correctly is that it is massively complicated.
Caleb
The benefit of XWQL was that it allowed to write
domain specific
queries, which are shorter and easier to understand (at least in theory).
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Looking at the specifications I have rewritten
the example query in compliant JPQL and JDOQL.
I wrote these so that they would work if all objects were custom mapped which is similar
to the
appearance XWQL gives.
XWQL:
(SELECT doc.fullName FROM XWikiDocument as doc) where doc.author =
'XWiki.LudovicDubost' and
doc.object(XWiki.XWikiUsers).email like '%xwiki.com'
JPQL:
SELECT doc.fullName FROM XWikiDocument as doc, IN(doc.xObjects) obj WHERE obj.className
=
'XWiki.XWikiUsers' and obj.email LIKE '%xwiki.com'
JDOQL:
SELECT this.fullName FROM XWikiDocument WHERE this.xObjects.containsValue(obj)&&
obj.className ==
"XWiki.XWikiUsers"&& obj.email.startsWith("xwiki.com")
I understood that XWQL was simply a translation scheme which made it appear that we were
using JPQL
with the schema we wanted when really we were using HQL with the schema we had. Given
that it is not
compliant JPQL that is not the case.
I think when we update the schema, we should cut our losses with this thing and move to
something
which has a reference document and is more widely used.
WDYT?
Caleb
The JPQL specification (originally called EJBQL):
ejb-3_0-fr-spec-ejbcore.pdf chapter 9.
http://jcp.org/aboutJava/communityprocess/final/jsr220/
The JDOQL specification:
jdo-3_0-mrel3-spec.pdf chapter 26.
http://db.apache.org/jdo/specifications.html
Easy to read, example rich descriptions:
http://www.datanucleus.org/products/accessplatform_3_0/jpa/jpql.html
http://www.datanucleus.org/products/accessplatform_3_0/jdo/jdoql.html