Over-eager fetching?

kev160967 · **Posted:** Wed May 14, 2008 11:35 am

Using the mappings below (which I've cut down for clarity), and executing the query specified, I find that NHibernate is generating a single select on the Clients table, as I'd expect, but then is hydrating each of the freightpayers in turn (ie, a query for each) as well. I tried adding the lazy="proxy" attribute to see if that would make a difference, but it didn't help. Can someone tell me what I'm doing wrong?

Hibernate version:
1.2GA

Mapping documents:

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Domain" assembly="Saturn.DAO">
 <class name="Saturn.DAO.Domain.Client, Saturn.DAO" table="Clients" >
    <composite-id name="ID" class="Saturn.DAO.Types.DBKey">
      <key-property name="Prefix"/>
      <key-property name="ID"/>
    </composite-id>
    <one-to-one name="Freightpayer" lazy="proxy" class="Saturn.DAO.Domain.Freightpayer, Saturn.DAO" />    
 </class>
</hibernate-mapping>

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="Domain" assembly="Saturn.DAO">
<class name="Saturn.DAO.Domain.Freightpayer, Saturn.DAO" table="FreightPayers">
    <composite-id name="ID" class="Saturn.DAO.Types.DBKey">
      <key-property name="Prefix"/>
      <key-property name="ID"/>
    </composite-id>
    <one-to-one name="Client" class="Saturn.DAO.Domain.Client, Saturn.DAO" constrained="true" />
 </class>
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():
session.CreateQuery("FROM Client C ORDER BY C.Name").List(Of Domain.Client)()

Name and version of the database you are using:
MS SQL Server 2005

wolli · **Posted:** Wed May 14, 2008 12:31 pm

This is the default behavior for fetching joins. There are several ways around that. You can find more information on that in the reference documentation in chapter 15.1 "Fetching Strategies".

In short you can

1) add fetch="join" to the association
2) modify your query to

FROM Client C inner join fetch C.Freightpayer ORDER BY C.Name

kev160967 · **Posted:** Wed May 14, 2008 5:27 pm

wolli wrote:

This is the default behavior for fetching joins. There are several ways around that. You can find more information on that in the reference documentation in chapter 15.1 "Fetching Strategies".

In short you can

1) add fetch="join" to the association
2) modify your query to

FROM Client C inner join fetch C.Freightpayer ORDER BY C.Name

Hi Wolfgang,
The thing is, I don't want it to fetch the freightpayer at all in this case. So, rather than finding a way to fetch both entities at once, I'm looking for a way to only fetch the client and leave the freightpayer as a proxy.

Kev

Nels_P_Olsen · **Posted:** Wed May 14, 2008 5:50 pm

From what I remember, NHibernate 1.x doesn't respect the lazy attribute on one-to-ones. I thought this was going to get fixed in 2.0, but I haven't tried that version yet ...

kev160967 · **Posted:** Thu May 15, 2008 5:25 am

Nels_P_Olsen wrote:

From what I remember, NHibernate 1.x doesn't respect the lazy attribute on one-to-ones. I thought this was going to get fixed in 2.0, but I haven't tried that version yet ...

Ah, that would explain what I'm seeing. I'll have to take a look at 2.0

Kev