I have a two tables, basically a parent table and a child table. I want the parent object to contain a set of child ids as opposed to references to the child objects themselves. I feel I set this up propertly in the hbm.xml file (see below). However, when I access all the parent objects I see that hibernate executes a select statement for every parent row, instead of a single join! Can this be right?



In my DAO object I execute: session.find(from Parent);

The resuling sql is basically:
select * from PARENT
select * from CHILD where ParentID = ?
select * from CHILD where ParentID = ?
select * from CHILD where ParentID = ?
.
.

I would expect it to be something more like:
select * from Parent p inner join Child c on p.id=c.parentID


Using hibernate 2.1.

Thanks,
Thaddeus

According to me you have to use the join fetch clausule in your statement but watch out, it has some strange side-effects. Try to do a test with parents with and without children; you will end up by having as many parents as there are children, similar to the result of an sql-statement, if I remember correctly.

At some point proxies come in here, but I don't know how it works; also check out the lightweight/heavyweigth design pattern on the wiki area.

Hope it helps,

Jan

Hi,

I have a similar issue.I would like to impleent parent child functionality.
There is a set of students with one classRep for the class.
I made this as a subclass of the "student" class.
Now I want to write a query that would pull out all students under a single particular classRep

i am writing my query as:

select * from Parent p inner join Child c on p.id=c.parentID ...

so my actual query is:

final String QUERY =
"from Student s inner join classRep c on t.id=c.parentID where d.class=" + false +"where d.id =?";

Using Hibernate ersion:

version 2.0.3, 27 August 2003


But this gives me error:

com.dynetics.gmpm.db.DatabaseException: net.sf.hibernate.JDBCException: Could not execute query: Syntax error or access violation, message from server: "You have an error in your SQL syntax near 'student1_.ID='gdavid' and student0_.classRep=student_.id)' at line 1"

Any tips....
Thanks much in advance.

As a addendum to above post, how to access subclass (classRep) and use classRep.id = student.id????

(problem is i dont have a table per se named "classRep" but just a subclass,, so I guess I cant use classRep.id in my SQL query...if so, looking for alternate ways to rephrase my query....

Thanks a lot!

1 more addition.....classRep is the classRepresentative....

Thanks!

Just use outer-join=true and set hibernate.max_fetch_depth to positive value.

Thanks for the reply.
Will I be able to set these values in my query...
my query is as follows:

final String QUERY = "from Student s inner join ClassRep c on t.id=c.parentID where d.class=" + false +"where d.id =?";

Thanks for the reply.
Will I be able to set these values in my query...
my query is as follows:

final String QUERY = "from Student s inner join ClassRep c on t.id=c.parentID where d.class=" + false +"where d.id =?";

ok...i added the above (fech_size and outer_join in my hiberntae.properties file).
Now I am getting :
net.sf.hibernate.QueryException: outer or full join must be followed by path expression


Thanks for the hel!