Re: [xwiki-devs] [proposal] XWiki Query Language implementation

Hi, devs. I would like to discuss about the new xwiki query language. http://dev.xwiki.org/xwiki/bin/view/Design/XWikiQueryLanguage We need to choose a syntax and data model of the query language There are some examples in http://dev.xwiki.org/xwiki/bin/view/Design/XWiki+Query+Language+Specificati… I already have a prototype based on my JPQL parser (SableCC based) and hql generator. It is quite easy to modify syntax and generator. Results of my query parser research in the end of the message. I propose: 0) Name: XWiki Query Language, XWQL as a name of the new language.

1) Data Model: Choose query method #1 from specification http://dev.xwiki.org/xwiki/bin/view/Design/XWiki+Query+Language+Specificati… with corrections: add Document as a virtual class for our XWikiDocument. use "docalias.XWiki.ClassName instead" of "XWiki.ClassName". docalias is some alias for Document. add optional select clause. example: "select doc.fullName from Document as doc, doc.XWiki.XWikiUsers as user where user.email like '%xwiki.com' and doc.author=:username"

"select doc.fullName from Document as doc" may be omitted. It will be added if there is no Document in query statement. So "from doc.XWiki.XWikiUsers as user" is correct query statement. It is possible to use several documents and objects in one query. Attachment, Class, and other xwiki entities will be added later if needed. 2) Syntax: XWQL will be JPQL subset. (hint: JPQL is part of Java Persistance API standard, JSR#317. HQL is a superset of JPQL. Hibernate support JPA) All JPQL features and all hibernate data model will be accessible for hibernate store. But it is not true for JCR store. Only described data model will be available for XWQL on JCRStore. (But we may add some extensions later) In JCRv2 will not work (JCRSQL2 constraint): arithmetic expressions (+-*/) aggregation funtions (max,min,sum,avg) some other functions In JCRv1 also will not work (XPath constraint): query on several documents (from Document as doc1, Document as doc2) Some JPQL limitations compared with HQL: no arithmetic expressions (+-*/) in select clause aliases at from clause are mandatory (from Document as alias) So the main idea is to use simple JPQL preprocessor to rewrite virtual data model to real. This is quite easy for HQL and JCRSQL2. But it is hard(but doable) for JCRv1 XPath.

WDYT? Appendix: I researched a many of query engines and found nothing appropriate. All query engines/parsers is either very specific or cannot be used standalone or cannot be used as a preprocessor. JCRSQL2 language parser from Jackrabbit is still unusable. Next I researched a parser generators and found that SableCC is best choose for my needs. Other tools (ANTLR, JavaCC, Cup, Beaver) requires much more hand work to write parse tree (AST) and preprocessors (Visitors and ast.toString). JTB and JJTree also generate AST and visitors, but SableCC generated code is much more clean. SableCC generate all of this from one clear grammar file. Maybe it is not as perfect as hand-written one, but it is quite suitable. Reason to choose sql-like syntax: XPath isn't still much spread. XPath language is deprecated in JCRv2. JCRv2 uses JCRSQL2 and criteria-like AQM instead. JCRSQL2 is much more powerful (in expression sense) than JCR's XPath and JCRSQL1. -- Artem Melentyev _______________________________________________ devs mailing list devs(a)xwiki.org http://lists.xwiki.org/mailman/listinfo/devs