Hi,
I am a newbie in OJB and an now trying the OJB using the ODMG API. I run the
tutorials on the OJB website successfully. But when I am trying one of my
own project, I was stuck in two problems,
1)
for the query string, if I use "select p from Project where companyCode = $1
and billingCode= $2;" everything is fine. But if I am trying to use the
alias for the object, replacing the above query with "select p from Project
p where p.companyCode = $1 and p.billingCode= $2;" there will be exception
thownn,
line 1: unexpected token: p
java.lang.NullPointerException
.....
The following is the code.
public Project locateProjectByCodes(String company_code, String
billing_code)
{
String oqlQuery = "select p from Project where companyCode = $1 and
billingCode= $2";
Database db = odmg.getDatabase(null); // the current DB
Transaction tx = null;
Project oneInstance=null;
try
{
// 3. open transaction
tx = odmg.newTransaction();
tx.begin();
// 4. acquire write lock on new object
OQLQuery query = odmg.newOQLQuery();
try
{
query.create(oqlQuery);
System.err.println("finished creating query");
}
catch(QueryInvalidException e)
{
System.err.println("query problem!");
}
query.bind(company_code);
query.bind(billing_code);
DList result = (DList) query.execute();
java.util.Iterator iter = result.iterator();
// 5. commit transaction
tx.commit();
//6. loop the result collection
if (iter.hasNext())
{
oneInstance = (Project) result.get(0);
}
logger.warn("locateProjectByCodes: "+oneInstance.getCompanyCode());
}
catch( Exception e )
{
System.err.println(e.toString());
tx.abort();
e.printStackTrace();
// e.printStackTrace(logger);
// Code omitted for tutorial brevity....
}
return null;
}
2) how to query two or more tables? Like the above example, say I have a
table Employee (to simplify the question, we assume it is 1:1 relationship
between these two tables, each employee works on one project)and I want to
get the project information a specified employee works on. With sql, I would
write as "select p.* from Project p, Employee e where
p.ProjectId=e.ProjectId and e.EmployeeName='me'", but how to do this with
ODMG query? I read all the tutorials and more than one examples on internet,
but all of them only query one table each time... In fact, when I tried to
write the OQL, like the above example, the exception reported my second
table name as unexpected token.
Thank you and I am waiting in such eagerness for your help.
Best,
Jack
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