db-ojb-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Christian Lipp" <c.l...@xion.at>
Subject RE: Is it possible to force OJB not use execute a prepared statement?
Date Wed, 04 Jun 2008 09:06:46 GMT
Hi Roger,

you are right with the chess match ....

I understand your point now, but we are not using a strategie at all (which
means we have exactly one strategie and it's hardcoded).
So we have always the same way to convert a boolean, we always enclose
strings with quotes, and so on...

The whole function looks like this:
	private static SimpleDateFormat df_date = new
SimpleDateFormat("yyyy-MM-dd");
	private static SimpleDateFormat df_time = new
SimpleDateFormat("HH:mm:ss.SSS");

	public static String asDBParameter(Object value)
	{
		if (value instanceof Number)		
			return value.toString();

		if (value instanceof String || value instanceof Character)
			return "'" + escapeString(value.toString()) + "'";

		if (value instanceof Timestamp)
			return "'" + value.toString() + "'";

		if (value instanceof Time)
			return "'" + df_time.format((Time)value) + "'";
			
		if (value instanceof Date)
			return "'" + df_date.format((Date)value) + "'";
			
		return value.toString();
	}

That's enough for our needs.

But when you want to implement a strategie and you need class descriptor or
field descriptor,
then I would override all functions which are calling appendParameter (for
example appendSelectionCriteria) and would provide a myAppendParameter,
which I would call from the overriden functions. The
myAppendParameter-function can have more arguments for strategie handling.

The signatur for appendSelectionCriteria is:
	void appendSelectionCriteria(TableAlias alias, PathInfo pathInfo,
SelectionCriteria c, StringBuffer buf)

With the first two parameters you could call
	protected FieldDescriptor getFieldDescriptor(TableAlias aTableAlias,
PathInfo aPathInfo)

and then you can give the field descriptor to myAppendParameter and from
there to asDBParameter and in this function you can perform your strategie.

Hope that helps,
CL

-----Original Message-----
From: Janssen, Roger [mailto:roger.janssen@ibanx.nl] 
Sent: Donnerstag, 08. Mai 2008 11:39
To: OJB Users List
Subject: RE: Is it possible to force OJB not use execute a prepared
statement?

Hi Christian,

I am also late in my response, this thread feels like a long distance chess
match communicating the moves by post (not email that is..) :)...

I understand you implemted a method "public static String
asDBParameter(Object value)", but with this solution, one of my questions
is: where/when are the conversion-strategies executed? The logical location
would be within this method, but then we need more information within this
method. We need to know whether there is a strategy configured, so we need
to have either the class-desriptor and attribute name, or the
field-descriptor. But that is all missing. We do need this because you just
cannot convert the java value object to the a string representation, and use
this within your query... A java boolean value may need to be converted into
an int value on a DB level... String clauses need to be enclosed within
quotes, integer values not... So more needs to be done with the java value
object... in the following order :
- apply conversion strategy
- convert to jdbc type
- convert to string representation (enclosed with quotes when required)

I am missing all this in your solution... Or I do not fully understand your
solution... Please explain me where/when in your solution the
conversion-strategies are appplied? Where/when are the values converted to
the proper JDBC type?

Greetings,

Roger Janssen
iBanx


-----Original Message-----
From: Christian Lipp [mailto:c.lipp@xion.at]
Sent: Thursday, April 17, 2008 5:04 PM
To: 'OJB Users List'
Subject: RE: Is it possible to force OJB not use execute a prepared
statement?

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.DynamicSqlSelect
Stat
ement

Regards, CL

-----Original Message-----
From: Janssen, Roger [mailto:roger.janssen@ibanx.nl]
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 
 
*************************************************************************
The information contained in this communication is confidential and is
intended solely for the use of the individual or entity to  whom it is
addressed.You should not copy, disclose or distribute this communication
without the authority of iBanx bv. iBanx bv is neither liable for the proper
and complete transmission of the information has been maintained nor that
the communication is free of viruses, interceptions or interference.  
 
If you are not the intended recipient of this communication please return
the communication to the sender and delete and destroy all copies.  





---------------------------------------------------------------------
To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
For additional commands, e-mail: ojb-user-help@db.apache.org



---------------------------------------------------------------------
To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
For additional commands, e-mail: ojb-user-help@db.apache.org


Mime
View raw message