Hi Roger, sorry for my delay.
> As I understand your example, it boils down to the appendParameter method
in your solution.
> That method adds the String representation of the value into the query
instead of the questionmark,
> used as argument placeholder in the prepared statement.
Exactly.
> In your example you use the asDBParameter method, but that one is not
available within 1.0rc5 version of OJB.
This should be a static function in your class that overrided
SqlSelectStatement (in my example it is DynamicSqlSelectStatement):
public static String asDBParameter(Object value)
{
if (value instanceof Number)
return value.toString();
// and so on for all your data types. Don't forgot to quote
strings.
This is all, you don't need the other things you mentioned.
It's just two classes, try it out.
You activate the class in your OJB property file with:
#---------------------------------------------------------------------------
-------------
# SqlGenerator
#---------------------------------------------------------------------------
-------------
# The SqlGeneratorClass entry defines the SqlGenerator implemementation to
be used
SqlGeneratorClass=org.apache.ojb.broker.accesslayer.sql.DynamicSqlSelectStat
ement
Regards, CL
-----Original Message-----
From: Janssen, Roger [mailto:[EMAIL PROTECTED]
Sent: Freitag, 04. April 2008 14:05
To: OJB Users List
Subject: RE: Is it possible to force OJB not use execute a prepared
statement?
Hi Christian,
It took me a while to have a closer look at your suggested solution, but I
finally had some time for it.
I do have a few/questions remarks. Maybe some it is caused by using
different versions of OJB, I do not know... We use 1.0rc5, but all the
things you describe, match this version as far as I can tell.
As I understand your example, it boils down to the appendParameter method in
your solution. That method adds the String representation of the value into
the query instead of the questionmark, used as argument placeholder in the
prepared statement.
In your example you use the asDBParameter method, but that one is not
available within 1.0rc5 version of OJB. However, it seems unlikely to me
that this method will do everything that is required. This method has just
one argument, a value represented by an instance of a java datatype
(integer/date/string/...). What the asDBParameter should do is the
following:
1. execute the fieldconversion for the attribute associated with this value,
which is given by the fielddescriptor 2. convert the outcome of the
fieldconversion into a JDBC typed object instance 3. add the string value
representation of the result from step 2 to into the query
For step one you require the classdescriptor and the fieldname, or the
fielddescriptor. The method asDBParameter does not have access to these
objects! They are not passed as arguments. Neither does the encapsulating
appendParameter method. So to make this work, these arguments should be
passed on, with all these nested method calls, which implies that you have
to change a lot of existing OJB method signatures (api interfaces). I am
reluctant to do so, because this would really complicate migrating to newer
versions of OJB.
Step two is not obvious as well. The current OJB solution embeds this
conversion inside the PreparedStatement class (used in the StatementManager
en Platform-implementation classes), it's like a black box, and you cannot
pull the converted argument values out of this statement. So I have no
solution yet to perform the conversion.
So how are the fieldconversions executed in your suggested solution, and
when does the java to jdbc datatype conversion takes place?
What also is missing in your solution is that in the end, the
StatementManager class (in 1.0rc5) binds all the values to the parameters.
This now should no longer be necessary, so you need to implement your own
JdbcAccessImpl class that implements a custom public ResultSetAndStatement
executeQuery(Query query, ClassDescriptor cld) throws
PersistenceBrokerException method. Within this method, the value/parameter
binding can be removed (call to method of StatementManager). Not doing this,
may not lead to errors, but doing this will remove a lot of now redundant
overhead.
So... a bit late... but here is my response on your suggested solution and
the exaample code you send.
Of course... there is always a chance that I got it completely wrong, please
let me know.
Greetings,
Roger Janssen
iBanx
-----Original Message-----
From: Christian Lipp [mailto:[EMAIL PROTECTED]
Sent: Wednesday, March 05, 2008 5:45 PM
To: 'OJB Users List'
Subject: RE: Is it possible to force OJB not use execute a prepared
statement?
In the OJB property file you have an entry "SqlGeneratorClass", which allows
you to choose a different generator implementation.
Override SqlGeneratorDefaultImpl. You have to implement a ctor, which calls
the super ctor and a function getPreparedSelectStatement(), which delegates
to your own Statement class.
This means that you handle SELECT statements, the rest (INSERT, DELETE,
UPDATE) is still handeld by SqlGeneratorDefaultImpl. If you want more, you
have to override getPreparedDeleteStatement for DELETE and so on. The class
would look like:
Then you have to write your own statement class (override
SqlSelectStatement). Again, you have to implement the ctors and override the
function appendParameter().
In this function you have to format the concrete value (function
asDBParameter):
/**
* Overridden method; appends the Parameter (real value) or the
sub-query.
* @param value the value of the criteria
*/
protected void appendParameter(Object value, StringBuffer buf)
{
if (value instanceof Query)
{
super.appendSubQuery((Query) value, buf);
}
else
{
buf.append(asDBParameter(value));
}
}
Since the statements are recursive, you also have to override
getSubQuerySQL:
/**
* Convert subQuery to SQL
* @param subQuery the subQuery value of SelectionCriteria
*/
protected String getSubQuerySQL(Query subQuery)
{
ClassDescriptor cld =
getRoot().cld.getRepository().getDescriptorFor(subQuery.getSearchClass());
String sql;
if (subQuery instanceof QueryBySQL)
{
sql = ((QueryBySQL) subQuery).getSql();
}
else
{
sql = new DynamicSqlSelectStatement(this,
getPlatform(), cld, subQuery, getLogger()).getStatement();
}
return sql;
}
You have to build your own strategie. I will post our strategies soon.
Greetings, CL
-----Original Message-----
From: Janssen, Roger [mailto:[EMAIL PROTECTED]
Sent: Mittwoch, 05. März 2008 15:02
To: OJB Users List
Subject: RE: Is it possible to force OJB not use execute a prepared
statement?
Hi Christian,
The problem, I believe, is with the number of parameters (parameter
markers) that crosses a certain boundary. We ran into an upper limit of 2000
(or something like that) on MSSQL server. That is a problem for us because
we sometimes generate queries that have more parameters (yes...
really), and then MSSQL server throws an exception.
So, I am very interested in your solution. It could help solve our problem
as well.
Roger Janssen
iBanx
-----Original Message-----
From: Christian Lipp [mailto:[EMAIL PROTECTED]
Sent: Wednesday, March 05, 2008 2:27 PM
To: 'OJB Users List'
Subject: Potential SPAM:RE: Is it possible to force OJB not use execute a
prepared statement?
Hi Roger,
OJB uses alsways prepared statements as armin said before, but do you have
problems with the prepared statements or with the count of parameter markers
(? in the where clause)?
I am asking because we did a lot of experiments with different
implementations (or specialisations) of SqlGeneratorDefaultImpl. The first
implementation was not using parameter markers at all.
So we used prepared statements without any parameter markers, which comes
close to dynamic statements (at least in my understanding and I think this
is what you need).
I would like to post what we did to discuss it here on the mailing list (we
are using db2 and could increase the performance 40% in online acces and 50%
in batch access).
CL
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