RE: Re: [OJB-developers] bug in sql generation

[<tr...@th...>]

It's your call, just bringing it to your attention.

Travis

---- Original Message ----
From: Oleg Nitz <on...@uk...>
Sent: 2002-05-30
To: obj...@li...
Subject: Re: [OJB-developers] bug in sql generation

On Thursday 30 May 2002 23:47, tr...@th... wrote:
> Because you are adding extra levels of complexity to OJB by trying to
> handle all databases internally.  Abstracting this out would make it much
> more modular and easier to maintain and implement new databases.  Not to
> mention better performance because crossdb uses a factory get the
> appropriate crossdb implementation, so there's not a bunch of if(db is
> mysql) else if(db is oracle), etc, etc.
Travis, the same thing is done in OJB: see Platform interface, 
PlatformFactory, and so on. And database handling is completely contained in 
ojb.broker.platforms module. The similar factory architecture is used in 
Castor. But I decided to introduce a classification of outer join syntax of 
*all* existing RDBMS (at least all that I know). At first I thought that 
there are 3 types of syntax: SQL-92, Sybase and Oracle. Than it turned out 
that SQL-92 syntax has 2 flavours: with braces and without braces.
And you are right, SqlStatement.java contains some number of if/else, which 
handles these 4 types of syntax. I don't believe that this is noticable for 
performance. But I suppose that the amount of code that handles database 
differences in OJB is less than in Castor (ojb.broker.platforms = 21K, 
org.exolab.castor.jdo.drivers = 217K), while OJB's SqlStatement.java is much 
more powerful than Castor's QueryExpression. 

> And it can support everything but unions (only because unions aren't
> supported in all dbs).  Joins are easily supported and Where statements can
> be infinitely nested.
And what about aliases?
Anyway we need to use unions with all databases that support them, thus 
CrossDB doesn't fit our needs. And supports less databases.
Not to mention better performance of SqlStatement because it does directly
  stringBuffer.append("X.col1");
  stringBuffer.append("=");
  stringBuffer.append("Y.col2");
instead of 
  SelectQuery sq = factory.getSelectQuery();
  ...
  sq.addWhereCondition("X.col1", WhereCondition.EQUAL_TO, "Y.col2");
  sq.execute();
I guess some number of additional objects are created inside the called 
methods. And how many if/else handle constants like WhereCondition.EQUAL_TO?
Don't tell me that with CrossDB we will increase performance ;o)

Regards,
 Oleg

_______________________________________________________________

Don't miss the 2002 Sprint PCS Application Developer's Conference
August 25-28 in Las Vegas -- http://devcon.sprintpcs.com/adp/index.cfm

_______________________________________________
Objectbridge-developers mailing list
Obj...@li...
https://lists.sourceforge.net/lists/listinfo/objectbridge-developers