Hibernate fails to read value from proxy object (created due to lazy loading) when this object participate in query formation.
I tried to explain the above problem with an example
Let’s consider four entities (sorry about class names I didn’t get any good names just gave random names)
Pt

*/
public class Pt {

private Long ptId;

private String ptName;

private Long ptNumber;

}

public class Tk {

private Long tk_Id;

private Pt pt;
}

Many to one relationship between Tk to Pt


public class Ot {

private Long otId;

private Set<Otm> otms;
}

Ot has set of Otm which has lazy loading option


public class Otm {

private Long otmId;

private Pt pt;

private Ot ot;

}

Otm has many to one relationship betwen Pt and Ot with lazy loading option.

Mapping files

<class name="com.hibernate.test.Pt" table="PT">

<id name="ptId" column="PT_ID" type="java.lang.Long"/>
<property name="ptNumber" column="PT_NBR" type="java.lang.Long"/>
<property name="ptName" column="PT_NAME" type="java.lang.String"/>

</class>



<class name="com.hibernate.test.Tk" table="TK">

<id name="tk_Id" column="TK_ID" type="java.lang.Long"></id>

<many-to-one name="pt" column="PT_NB" class="com.hibernate.test.Pt" property-ref="ptNumber" not-null="true"></many-to-one>
</class>


<class name="com.hibernate.test.Ot" table="OT">
<id name="otId" column="OT_ID" type="java.lang.Long"></id>

<set name="otms" lazy="true" inverse="true" cascade="all">
<key column="OT_ID"></key>
<one-to-many class="com.hibernate.test.Otm" />
</set>


</class>


<class name="com.hibernate.test.Otm" table="OTM">

<id name="otmId" column="OTM_ID" type="java.lang.Long"></id>

<many-to-one name="pt" column="PT_ID"
class="com.hibernate.test.Pt" lazy="proxy"/>

<many-to-one name="ot" column="OT_ID"
class="com.hibernate.test.Ot" lazy="proxy"/>

</class>

All of these have default access as field.

My use case is
I query for Ot > select Otm > get Pt from Otm
Create new instance of Tk set pt to Tk and save Tk
Code

Session session2 = HibernateSessionFactory.getSession();
session2.beginTransaction();

Ot ot2 = (Ot)session2.get(Ot.class, 1002l);
Tk tk = new Tk();
tk.setTk_Id(1l);

tk.setPt(//call the domain method to select one Otm from Ot);
session2.save(tck);
session2.getTransaction().commit();

This gives me a sql exception with message
“Attempt to insert null into a non-nullable column: column: PT_NB table: TK in statement [insert into TEST.TK (PT_NB, TK_ID) values (?, ?)]”

When I debugged the code I could see that Cglib proxy of Pt was set to Tk and while dehydrating this entity, it tried to read ptNumber (it is not primary key) from the proxy. But PojoEntityTuplizer(AbstractEntityTuplizer).getPropertyValue(Object, int) returns null when access is set as field level.

Any suggestions to solve this problem will be helpful. I don’t want to have getter method in my entities as value accesses in entities are done through some domain logic API's.

Thanks in advance
Hari

I have the same or a similar problem.




It is difficult to diagnose but it happens about 80% of the time when executing the code and it has NEVER happened if I step through the code via the debugger. This leads me to think that hibernate is loading the proxy objects with a separate thread and maybe there is a thread join problem if you are lazy loading through multiple objects.

I have never received a null if I try to lazy load one class
i.e. Class c = student.getClass() is never null.

I don't think it creates thread but what I found is, while retrieving the value
field.get(proxy) doesn't return any value. Looks like proxy is not created properly.

I have the exact same issue. Hibernate konks off with exception that it cannot insert null value

We've just encountered the same issue.

UPDATE:
Issue was due to the javassist 3.17.1 library. Updating to Hibernate 4.1.11 with javassist 3.15.0 solved the problem.

See:
https://hibernate.atlassian.net/browse/HHH-7884

Thanks in advance!