Hi Flavio,I have attached a TreeWalker class to https://issues.apache.org/jira/browse/DERBY-3946 This may help you explore the AST.
Hope this helps, -Rick Rick Hillegas wrote:
Hi Flavio,I don't think that we have a good primer on the AST nodes. However, you can get some sense of what the nodes mean by building the Derby javadoc and looking at the javadoc for the package org.apache.derby.impl.sql.compile.Now that you've gotten over the hard hurdle of building the Derby classes, building the javadoc is easy:ant -quiet javadocThis will build the javadoc into the directory javadoc/engine. Once you have built the engine javadoc, browse to the org.apache.derby.impl.sql.compile package. The header comments on the classes are usually pretty helpful. I also recommend taking a look at the tree view of that package. You will see that the AST nodes are all of the classes indented under QueryTreeNode.Understanding the AST graph takes some patience. There are two useful techniques for figuring out how the nodes snap together into a graph:1) The nodes themselves implement org.apache.derby.iapi.sql.compile.Visitable. That interface has one method, accept(). Not all AST nodes directly implement accept() so you may have to inspect their superclasses. The accept() method shows you what each node thinks its subnodes are. You can write your own tool to explore the graph by coding your implementation of the graph walker, org.apache.derby.iapi.sql.compile.Visitor.2) The nodes also implement a pretty-printing method, treePrint(). The treePrint() method is another example of what a node thinks its subnodes are. This is the method which ASTParser calls on the top node.That should get you started. The devil is in the details, but keep posting questions and I think you'll get to the bottom of it.Hope this helps, -Rick Flavio Palumbo wrote:Hi guys, I followed this post finding it very exciting, cause I post a similar question a while ago.Now I'd like to test the work submitted by Rick but I'm not so inside Derbyto catch he whole job I have to do. I understood that I have to : - download Derby sources (from where ?) - apply the patch suggested by Rich (seen the classes but not catch the lines of code) - recompile Derby (what libraries/jars I need to) - use ASTParser as suggested Can somebody give me a hint Thanks a lot Flavio-----Messaggio originale----- Da: news [mailto:[EMAIL PROTECTED] conto di Christian Riedel Inviato: giovedì 13 novembre 2008 6.37 A: [email protected] Oggetto: Re: Using derby to parse an SQL statement Hi Rick, at first thank you very much for your efforts so far. At a first glance your changes to the code seem to be exactly what we want. I will try if it works asap.To test it with the derby libs I'd have to work on the current trunk andapply the patch an then compile derby manually, right? I'll keep you updated Thanks for your help Christian Rick Hillegas schrieb:Hi Christian, I have created a JIRA to track this issue: https://issues.apache.org/jira/browse/DERBY-3946 I have attached to the JIRA a small patch which exposes the ASTproducedby the parser. I have also attached a simple program, ASTParser, which shows how to retrieve the AST from Derby. I am inclined to check this patch in to the trunk. Please let me know if you find thisuseful and ifyou would like me to port this patch to another Derby branch. Hope this helps, -Rick Christian Riedel wrote:Hi Rick, first of all thanks for your answer ... now the relations have become a lot clearer ... Your are right, there is a lot of things to be done that we probablydon't want to go through. You asked why we cannot take the whole derbyengine and use it ... well there is nor real reason not to do so. Theonly "problem" I see is, that derby is a dbms - if I am not mistaken - and we only have an SQL statement that we extract from a text file andwant tot analyze it to extract some metadata from it. So if we take the derby engine as it is, how can I prevent that we have to set up a "dummy" DB in order to be able to actually use thje parsing feature .... I hope you see my point. We could live with setting up a dummy DB ... and I do think that the derby AST offers all information we need. It's just that I don't see how we can set this thing up. So having a dummy DB is necessary to be able to intercept the parsing process to get hold of the AST? Can we actually access the AST if we choose to set up a dummy DB? I think that would be something we could live with ;-) Thanks for your support Christian Rick Hillegas schrieb:Hi Christian, I think you will have difficulty isolating the Parser from the rest of the SQL interpreter. In theory, you should be able to isolate thecompiler from the execution engine and the storage layer--but that isan untested theory. The Parser wants to turn out abstract syntax trees (AST). Ideally,the Parser would just need to ask a NodeFactory for AST nodes and youcould supply your own NodeFactory. But I think that there is a fair amount of coupling between the Parser and Derby's concrete implementation of NodeFactory. I think that you could uncouple the two, but you may not want to spend your time on that. So the Parser is going to force you to pull in the AST nodes. Once you do that, you will end up with the whole compiler. In particular, the AST nodes (and the Parser itself) expect that you will supply an implementation of LanguageConnectionContext, the master state variable for the whole SQL interpreter. Untangling that requirement is another chunk of work you may not want to do. Then there is the Monitor. It has been a while since I was in that code but I seem to recall that fairly early on the Monitor wants to fault in a storage layer. In theory you ought to be able to supply the Monitor a list of modules that doesn't include a storage layer.But since no-one runs in this configuration, there are probably a lotof undocumented surprises that you may not want to fix either.Can I ask you what breaks if you just pull in the whole Derby engine?Are you concerned that you will fault in too much code that you barely use? Are you concerned that you'll end up with a dummy database that you don't need? Are Derby's AST nodes not a usable representation of statement syntax? Thanks, -Rick Christian Riedel wrote:Hi there, we are working on a small project where we need to analyze an SQL statement that can be of any kind: very simple, with inner selects, complex join etc. We figured it inappropriate to start to write our own parser when there are other projects, like derby, out there that can do it much better than we would possibly do ... so this was our idea: Can we use derby to create an instance of Parser (org.apache.derby.iapi.sql.compile.Parser.class) and let our SQL statement be parsed by calling the parse() method on this instance? What we want to have is a syntax tree of the statement that allows us to see which tables and which fields are accessed / included in the statement (including any possibly done "renames" á la SELECT street AS "ADDRESS" FROM USER_DATA ). The problem is, that we are stuck ... we spent several days now to try to find the proper way to create an instance of the Parser. Is it possible at all without having to set up a running derby system? Is the Monitor class the right entry point? How can we create a CompilerContext so that a Parser instance can be created? This sure is off-topic but we don't see any way through all this. Can you help us? Thanks in advance Christian-- To reply to this posting directly use the following address and remove the 'NO-SPAM' part: [EMAIL PROTECTED]-----------------------------------------------------------Il presente messaggio non costituisce un impegno contrattuale tra SILMA S.r.l. ed il destinatario.Le opinioni ivi espresse sono quelle dell'autore.SILMA S.r.l. non assume alcuna responsabilita riguardo al contenuto del presente messaggio.Il messaggio è destinato esclusivamente al destinatario. Il contenuto e gli allegati sono da considerarsi di natura confidenzialeNel caso abbiate ricevuto il presente messaggio per errore siete pregati di comunicarloalla casella [EMAIL PROTECTED]
