So let me be a pest some more ;-) See my questions mixed in to your comments Thomas :-)
> -----Original Message----- > From: Mahler Thomas [mailto:[EMAIL PROTECTED]] > Sent: Monday, September 02, 2002 1:27 AM > To: 'OJB Users List' > Subject: AW: SELECT statements and OJB > > > Hi, > > > I am extremely new to OJB. But something I was wondering > > regarding using the > > PB API is whether or not you can select the particular field > > (attribute) you > > want returned. For example, i have a sql statement like such > > SELECT ID, > > FIRSTNAME, LASTNAME FROM PEOPLE WHERE ID=2. The PEOPLE table actually > > contains the following fields: ID, FIRSTNAME, LASTNAME, ADDRESS, CITY, > > STATE, ZIP, NOTES. In OJB PB it seems that all i can do is > > the equivalent of > > SELECT * FROM PEOPLE WHERE... I don't want to select all (*) > > the fields > > everytime. In the afformentioned sql statement i want to just > > produce a list > > of People objects that have only the id, firstname and > > lastname variables > > populated. Am i missing something > > Yes! > > 1. OJB does *not* perform "select * from", for queries! > If you look up objects of class x OJB will read the class-descriptor for > class x and determine all necessary columns to materialize an x instance. > The performed select contains all those columns. > > If you want to limit the number of columns you can modify the > class-descriptor for class X do get a reduced number of columns. > So, if i needed a full person to be materialized in one place and only the id, firstname and lastname elsewhere then I would have to write a couple of classes and their associated class-descriptor. For example my PersonName and Person would be two different object classes that are populated from the same table (PEOPLE). > 2. OJB does have a ReportQuery concept. ReportQueries do not generate > collections of fully materialized entity objects, but a Simple tabular > representation of resultsets. > > You can use PersistenceBroker.getReportQueryIteratorbyQuery(q) do iterate > over a query resultset. > You can also combine ReportQueries with QueryBySql Queries to perform > arbitrary freeform SQL. > Is there some thorough docs on this. I looked into the javadocs but it left me with several questions. What do you mean by tabular representation of resulsets? What does tabular mean? Also what is the ReportQuery meant to address or solve in the course of coding with OJB? How is the getReportQueryIteratorByQuery(Query query) different from getIteratorByQuery(Query query)? How do i combine ReportQueries with QueryBySql? I am sorry i have so many questions. I noticed that something the documentation lacks is a good visual diagram of the components contained within OJB and theif defined purposes in the course of the various use cases in ojb. I am very grateful for the time and energy that you have put in Thomas. I would like to help. As i understand this more I would like to put together a reference that clearly defines the different elements of OJB's persistence broker and how they are related to one another. I am not familiar enough with JDO and ODMG to do anything there. If there is already a resource like this it would be great to know about. Also, on a side note. I was looking at the Proxy sample code in the Advanced O/R Mapping and i noticed in the proxy sample that the super(uniqueId, broker) was being called and when i looked into the VirtualProxy class i found no constructor that would be called with the provided parameters in the super method call. Has the base code changed or did i miss something in the javadocs? > > > or is this just not > > possible apart from > > using a sql statement call from the PB API's QuerBySQL (if > > that would even > > work cuz i haven't tested it). If i can't be selective about > > the data that > > populates my People object then I will produce a lot of > > unecessary data > > collection and population from the database to my objects. > > Especially if the > > NOTES field can contain 250k of data (an exaggeration of > > course but the > > point is there). The thing that attracted me to OJB was how > > easy it is to > > code to a database with OO patterns. I hope the solution > > isn't something > > that requires me to write some kind of extra class each time > > i want to limit > > what is populated in my People class or require me to create > > a whole new > > class to handle just the listing of the basic people info. > > This would be a third solution, but as there are two others it's not > mandatory... Thanks, Brandon Goodin Phase Web and Multimedia P (406) 862-2245 F (406) 862-0354 [EMAIL PROTECTED] http://www.phase.ws -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
