Thanx for the insight. The only reason that I didn't go with ReportQueries is because the application I have needs to be configured w/ the repository.xml file, not by myself, but by the client - someone with absolutely NO experience or knowledge of OJB. Because the database schemas could change between clients and I wanted to use the same application per client, I couldn't use ReportQueries because you can't configure them with the XML descriptors.
--Bobby
Antonio Gallardo wrote:
On Lun, 24 de Enero de 2005, 8:32, Bobby Lawrence dijo:
Not having an alias would allow you to use functions and string literals. You could specify a string literal in the field-descriptor like this:
<field-descriptor name="myField" column="' 'a string literal' ">
This would give you the same value for every class instance, which might
not seem that useful at first, but this is exactly what I needed in my
project for a brief time. At the time, I was expecting values from the
database where the field did not exist yet and I needed something to test.
Is posible to test for null?
You could also specify functions in the field-descriptor like this:
<field-descriptor name="wholeName" column="CONCAT(CONCAT(firstname, ' ',
lastname) AS wholename">
If using an Oracle database, this would concatenate the first and last
names to give you a whole name.
Could be used in a ReportQuery if we make it resolve more than 1 field in a expresion.
Another example on concatenation w/ Oracle without using the function:
<field-descriptor name="wholeName" column="firstname || ' ' || lastname
AS wholename">
Works in PostgreSQL too, again the solution is using a ReportQuery that solves multiplefields in one expresion.
All of these should be possible if OJB didn't use table aliases in its
generated SQL statements.
While the theory indicates that each field in the database must have a unique name. In the practice, we found that in some databases, the users choose same names for fields in diferentables. Sample:
table1.ID table2.ID
the same field name "ID" should be resolved and this is why I think OJB choosed to use SQL table alias to resolve this names.
What IS the benefit of using an alias?
Not being a big fan of SQL alias, but what I understand:
1-This is convenient when you want to obtain information from two separate tables (the technical term is 'perform joins'). The advantage of using a table alias when doing joins is readily apparent when we talk about joins.
2- Generate shorter queries:
SELECT from mylongnametable.fieldA, mylongnametable.fieldB FROM mylongnametable;
vs.
SELECT from A0.fieldA, A0.fieldB FROM mylongnametable A0;
Hope this helps,
Best Regards,
Antonio Gallardo.
--------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
-- ---------------------------- Bobby Lawrence MIS Application Developer
Jefferson Lab (www.jlab.org)
Email: [EMAIL PROTECTED] Office: (757) 269-5818 Pager: (757) 584-5818 ----------------------------
