Hello Bart,
Use the FETCH or LEFT_FETCH query hint instead of the BATCH hints so
that the relationship is retrieved in the same statement - forcing the
objects to be built from the same row rather than allowing the lazy
relationship to use a separate batch query to bring in the values.
You can also use JOIN FETCH in your JPQL instead of using a query hint
in the same manner.
Best Regards,
Chris
On 08/12/2010 10:24 AM, Bart Kummel wrote:
Hi list,
I'm trying to optimize my application. I've set some relationships to
LAZY fetching, since we have a lot of UI pages where we don't need the
referenced collection(s). Let's have a look at a simplified example.
Say we have the following entities:
@Entity
public class Invoice {
@OneToMany(mappedBy = "invoice", fetch=FetchType.LAZY,
cascade={CascadeType.REFRESH, CascadeType.MERGE})
private List<InvoiceLine> invoiceLines;
}
@Entity
public class InvoiceLine {
@ManyToOne
@JoinColumn(name = "INV_ID", referencedColumnName = "INV_ID")
private Invoice invoice
}
I have a named query to get the invoice without the invoice lines. But
for the UI page where we do need the invoice AND the invoice lines, I
want to create a named query to get everything as efficient as
possible. So I read http://java-persistence-performance.blogspot.com/
and decided to go for batch reading. So I have code like this:
Query q = getEntityManager().createQuery("select i from Invoice i
where i.invoiceId = :invoiceId");
q.setParameter("invoiceId", invoiceId);
q.setHint(QueryHints.BATCH, "i.invoiceLines");
q.setHint("eclipselink.batch.type", "EXISTS");
I've set the EclipseLink logging to FINE. I can see in the logged SQL
statements that the data is retrieved from the database as expected.
However, as soon as the Invoice object gets detached and I call
getInvoiceLines(), I get the EclipseLink-7242 error, about traversing
LAZY relationships. I can resolve this by calling getInvoiceLines()
directly after the query, but I wonder if there's a more elegant way to
fix this.
Best regards,
Bart Kummel
--
___________________________________________________________
Bart Kummel
Author of the book Apache MyFaces 1.2
Web Application Development
blog: BK |
twitter: @bkummel
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