lazy loading of n-to-1 relationship

jpompeii3 · **Posted:** Fri May 13, 2005 3:27 pm

I'm having problems getting a n-to-one relationship to work via lazy activation. Basically, I have a User class which has a <many-to-one> property to an Address.
The mapping def for the relationship in User looks like:

Code:

<many-to-one name="UserAddress"
    class="NHibernateTestModel.Address, NhibernateTestModel"
    column="addID" cascade="all"/>

The Address class mapping contains the lazy="true" attribute:

Code:

<class name="NHibernateTestModel.Address, NhibernateTestModel" table="Address" lazy="true">
    <id name="ID" column="addID" type="Int32" unsaved-value="0"> 
        <generator class="assigned" /> 
    </id> 
    <property name="Address1" column="Address1" type="String" length="255"/> 
    <property name="City" column="City" type="String" length="255"/> 
    ...

</class>

In the test application, I access the address like this:

Code:

User user = (User)session.Load(typeof(User), "john");
Address addr = user.UserAddress;
string street = addr.Address1;

The returned address object ("addr") is an instance of CProxyTypeAddress_ISerializable_INHibernateProxy2. When invoking the property accessor Address1, no access to the database is ever done to fetch the Address instance, and the value null is returned. If I remove the "lazy=true" line to the Address class mapping, the address object is fetched with the user but everything is returned correctly.

Any idea what I'm doing wrong here?

thanks,
--john

sergey · **Posted:** Sat May 14, 2005 1:55 pm

Did you make all the properties of Address virtual? If they are not virtual, there is no way to intercept the call to them and load the object.

tinomen · **Joined:** Tue May 24, 2005 12:55 pm **Posts:** 56

I've been trying to figure this out. I've found nothing stating that if a class is lazy that the props need to be virtual. Is there more info about this? If so, could someone please post a url(s).

Quote:

Nevermind, found a link to the FAQ on JIRA that has a short blurb about proxies/lazy loading:
http://wiki.nhibernate.org/display/NH/Frequently+Asked+Questions

raulnunhez · **Posted:** Wed May 25, 2005 11:56 am

jpompeii3, I have the same problem with my classes. The proxy must be transparent, but I think that it isn't

Any idea??

jpompeii3 · **Posted:** Wed May 25, 2005 4:00 pm

Sergey was right. I had to put virtual on the property definitions in order to make this work. Once I did that, everything worked great.

BTW, Sergey, is there any real downside to adding lazy="true" on all class definition?

KPixel · **Posted:** Fri May 27, 2005 10:18 am

jpompeii3 wrote:

Is there any real downside to adding lazy="true" on all class definition?

You have to make sure you initialize all the proxies you will need before closing the session (ore reattach it to an opened session before)

jpompeii3 · **Posted:** Fri May 27, 2005 4:22 pm

KPixel wrote:

jpompeii3 wrote:

Is there any real downside to adding lazy="true" on all class definition?

You have to make sure you initialize all the proxies you will need before closing the session (ore reattach it to an opened session before)

I'm not sure what you're trying to say. Basically what I'm asking is that the lazy="true" on the class tags enables the proxying of the class when it's on the end of a one to one or many to one. If a class is not going to be proxied, does setting lazy="true" on the class tag for these classes matter. That is, is it ignored if proxying for that class is not needed.

The reason for asking is that we're generating the hbm.xml files from a UML model and it's a pain to know when setting lazy="true" is required on a class and it's subclasses

Guest · **Posted:** Mon Dec 12, 2005 3:15 pm

KPixel wrote:

jpompeii3 wrote:

Is there any real downside to adding lazy="true" on all class definition?

You have to make sure you initialize all the proxies you will need before closing the session (ore reattach it to an opened session before)

How does one reattach an object graph to a new session?

I am running into this issue in an ASP.NET environment where I am storing my objects into the viewstate and retreiving them on PostBack. After postback I am trying to access linked objects that I hadn't accessed on the initial page load and am getting the "no session" exception. I don't want to save any of the objects yet, as I have a multi-step wizard process (long transaction) where nothing should be saved to the DB until the final step.

KPixel · **Posted:** Tue Dec 13, 2005 8:39 am

Code:

session.Lock(myEntity, LockMode.None);