Hibernate create: null error

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Jacqui - 11 Oct 2005 17:40 GMT

Hi,

I have been puzzling over this for the last couple of days and was
wondering if any of you could help me.

I get the following error when I try to load a jsp in my webapp:

Error looking up property "town" in object type
"com.moveassist.reloassist.model.Address$$EnhancerByCGLIB$$48a8613c".
Cause: null

I know that the EnhancerByCGLIB part means that it has not initialised
the proxy but I am unsure why it would not do this and I also do not
know what the Cause: null might mean.

I have the following in Address.hbm.xml:

<class
name="com.moveassist.reloassist.model.Address"
lazy="true"
>

and in Company.hbm.xml (which has a many-to-one relationship with the
address table and is the object the Address is a property of in the
exception above) I have:

<many-to-one
name="address"
class="com.moveassist.reloassist.model.Address"
cascade="none"
outer-join="true"
update="true"
insert="true"
column="address"
/>

I have read in the excellent book 'Hibernate In Action' that setting
lazy="true" and outer-join="true" usually makes the proxy initialised,
but not in this occasion! Could someone please give me pointer in the
right direction!! If you need further info, please let me know.

Thanks in advance for your help and time.

Jacqueline

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Ross Bamford - 11 Oct 2005 18:23 GMT

> Hi,
>
[quoted text clipped - 40 lines]
>
> Jacqueline

I have seen similar errors from Hibernate when the reflection optimizer
couldn't find a class - it turns out it's hardcoded to the system
classloader for a number of things, so do you have any custom
classloading? I've found that 'lazy' usually does the trick to ensure
initialization is done properly, but that you have to take care to specify
'inverse' appropriately with bidi collections. I also like to specify the
collection lazy, rather than the class, but I guess it depends on what
you're trying to achieve.

Apart from that, make sure that you have a default constructor of at least
package private visibility, and ensure that your classes, getters/setters
and fields (obv) aren't final.

You might also add the following to your hibernate.properties:

hibernate.cglib.use_reflection_optimizer=false

And seeing what that does. You might find a (much) more descriptive error
message hiding there. I've had to use this before when there have been
problems with certain classes, though I can't remember the exact causes...

If you're still stuck, it would be helpful to see at least Address.hbm.xml
and hibernate.cfg.xml in full.

Signature

Ross Bamford (rosco@roscopeco.remove.co.uk)

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Jacqui - 12 Oct 2005 09:38 GMT

Thanks for your quick response!

I have checked both the Company and Address classes for final
fields/methods and there are none there.

I have also followed your suggestion and put the line in the
hibernate.properties file and this has not added any further info to
the error messages.

We are using Spring to initialize the beans, and the following is the
config in the spring.xml file:

<bean id="sessionFactory"
class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
<property name="mappingDirectoryLocations">
    <list>
        <value>classpath:/com/moveassist/reloassist/model</value>
        </list>
    </property>
    <property name="hibernateProperties">
    <props>
        <prop
key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
        </props>
</property>
    <property name="dataSource">
    <ref bean="dataSource"/>
    </property>
</bean>

This setup works fine for other classes/relationships, we are just
having problems with this one.

As requested, Address.hbm.xml in full:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping

<class
name="com.moveassist.reloassist.model.Address"
lazy="true"
>

<id
name="id"
column="id"
type="java.lang.Integer"
>
<generator class="native">

</generator>
</id>

<property
name="address"
type="java.lang.String"
update="true"
insert="true"
column="address"
/>

<property
name="street"
type="java.lang.String"
update="true"
insert="true"
column="street"
/>

<property
name="town"
type="java.lang.String"
update="true"
insert="true"
column="town"
/>

<property
name="county"
type="java.lang.String"
update="true"
insert="true"
column="county"
/>

<property
name="postalCode"
type="java.lang.String"
update="true"
insert="true"
column="postalCode"
/>

<many-to-one
name="country"
class="com.moveassist.reloassist.model.Country"
cascade="none"
outer-join="true"
update="true"
insert="true"
column="country"
/>



</class>

</hibernate-mapping>

Company.hbm.xml in full:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping

<class
name="com.moveassist.reloassist.model.Company"
>

<id
name="code"
column="code"
type="java.lang.String"
>
<generator class="assigned">

</generator>
</id>

<property
name="name"
type="java.lang.String"
update="true"
insert="true"
column="name"
/>

<many-to-one
name="address"
class="com.moveassist.reloassist.model.Address"
cascade="none"
outer-join="true"
update="true"
insert="true"
column="address"
/>

<property
name="accountsCode"
type="java.lang.String"
update="true"
insert="true"
column="accountsCode"
/>

<many-to-one
name="companyHead"
class="com.moveassist.reloassist.model.Employee"
cascade="none"
outer-join="auto"
update="true"
insert="true"
column="companyHead"
/>

<set
name="offices"
lazy="true"
cascade="all"
sort="unsorted"
>

<key
column="company"
>
</key>

<one-to-many
class="com.moveassist.reloassist.model.Office"
/>

</set>



</class>

</hibernate-mapping>

If it helps, we also have another class 'CorporateAccount' which has an
address, and this initializes properly.

Thanks for the help so far, I look forward to hearing from you again!

Jacqueline

Reply to this Message

Ross Bamford - 12 Oct 2005 11:02 GMT

> Thanks for your quick response!
>
[quoted text clipped - 4 lines]
> hibernate.properties file and this has not added any further info to
> the error messages.

Thanks for sending over your mappings! I have a few suggestions:

1) Check that the database column 'town' really does exist.

2) Remove 'lazy=true' from the class definition. I think you can only
switch _off_ laziness for a whole class.

3) Remove the 'outer-join=true' from the many-to-one entries. IIRC it's
not supported there (any more?).

4) Remove the 'insert' and 'update' entries, because they default true
anyway.

If none of that helps, next:

5) Disable laziness explicitly with 'lazy=false' on the many-to-one

5) Look into your cascades - why aren't you cascading events on that
class? Is there some particular reason for that? If so, are you making
sure you persist and update everything as required by the Company class?
If not, set cascade 'all' for now.

6) Comment out the 'town' property in Address.hbm.xml, to see if you still
get the problem. If so, it's likely the problem is actually a symptom of a
more specific problem loading that column from the database.

6) Set the property 'hibernate.show_sql' in either the config or your
hibernate properties. This will make hibernate output the SQL statements
it's about to execute to System.out. Look for the commands it executes
leading upto the problem. If nothing immediately seems wrong with it, fire
up the mysql console and try those same commands with some test data.

Unfortunately in my experience theres usually some trial and error
involved with fixing any reasonably complex hibernate model, and it's
often the performance optimizations that cause problems. IMHO there are
too many conditional features in hibernate, in that you can do this, but
only if you're doing this, and this, and not doing something else, so the
approach I usually use is to build the model incrementally, starting with
the very basics, and then gradually building in optimizations and stuff,
always checking each change still works.

> If it helps, we also have another class 'CorporateAccount' which has an
> address, and this initializes properly.

Good. The Address mapping itself looks okay (apart from the redundancy
mentioned above). Try comparing the way you've mapped the address from
there to see if anything's done differently.

Hopefully this will at least give a more descriptive error to work on ;)

Signature

Ross Bamford - rosco@roscopeco.remove.co.uk

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Hibernate create: null error

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