Hi Christian,
Standby. I will post some code showing how to do this later today.
Cheers,
-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 probably
don't want to go through. You asked why we cannot take the whole derby
engine and use it ... well there is nor real reason not to do so. The
only "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 and
want 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 the
compiler from the execution engine and the storage layer--but that is
an 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 you
could 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 lot
of 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" รก 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
