There is some fundamental thing about inheritance mapping that I don't get. I'm creating a generic attribute system, which should be able to store strings, floating point numbers and integers.
The abstract base class is called
AttributeValue, extended by
StringAttributeValue,
DoubleAttributeValue and
LongAttributeValue.
The test cases attempt to store and retrieve values of all three types. Storing the values goes fine, everything looks OK when I inspect the database.
I'm retrieving the values by calling
session.get(AttributeValue.class, id), which works fine for String values, but retrieving Long and Double values causes ClassCastException (see stacktrace below).
Retrieveing values by using concrete class names, like
session.get(DoubleAttributeValue.class, id), also works. However, to retrieve all attributes I would then have to
repeat
session.get for all concrete classes and aggregate the results, which seems counter-intuitive.
So the question is: How can I make
session.get(AttributeValue.class, id) return objects from the subclasses?
Hibernate version:
3.1rc2
Mapping documents:
Code:
<?xml version="1.0"?>
<!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.idium.ips.attributes.baseattributetypes.AttributeValue" table="ATTRIBUTEVALUES" abstract="true">
<id name="id" column="ID">
<!-- The identity generator strategy is not allowed in union subclass inheritance,
indeed the primary key seed has to be shared accross all unioned subclasses
of a hierarchy.
http://www.hibernate.org/hib_docs/reference/en/html/inheritance.html section 9.1.5 -->
<generator class="sequence"/>
</id>
<union-subclass name="com.idium.ips.attributes.baseattributetypes.StringAttributeValue" table="STRINGATTRIBUTEVALUES">
<property name="value" column="VALUE" type="string"/>
</union-subclass>
<union-subclass name="com.idium.ips.attributes.baseattributetypes.DoubleAttributeValue" table="DOUBLEATTRIBUTEVALUES">
<property name="value" column="VALUE" type="double"/>
</union-subclass>
<union-subclass name="com.idium.ips.attributes.baseattributetypes.LongAttributeValue" table="LONGATTRIBUTEVALUES">
<property name="value" column="VALUE" type="long"/>
</union-subclass>
</class>
</hibernate-mapping>
Code:
public void testStringValue() throws Exception {
AttributeValue<String> value = prepare("Tjorven", NOR_LOCALE, StringAttributeValue.class);
doAssertions(StringAttributeValue.class, value);
}
public void testDoubleValue() throws Exception {
AttributeValue<Double> value = prepare(3.14, NOR_LOCALE, DoubleAttributeValue.class);
doAssertions(DoubleAttributeValue.class, value);
}
public void testLongValue() throws Exception {
AttributeValue<Long> value = prepare((long) 2, NOR_LOCALE, LongAttributeValue.class);
doAssertions(LongAttributeValue.class, value);
}
public Session getSession() {
return sessionFactory.getCurrentSession();
}
private <T> AttributeValue<T> prepare(T value, Locale locale, Class<? extends AttributeValue<T>> valueClass) throws Exception {
AttributeValue<T> attributeValue = ((Class<? extends AttributeValue<T>>) valueClass).newInstance();
attributeValue.setValue(value);
attributeValue.setLocale(locale);
getSession().save(attributeValue);
getSession().getTransaction().commit();
getSession().beginTransaction();
return attributeValue;
}
private <T> void doAssertions(Class<? extends AttributeValue<T>> valueClass, AttributeValue<T> attributeValue) {
/** The next line fails with ClassCastException if (valueClass == LongAttributeValue.class || valueClass == DoubleAttributValue.class) **/
AttributeValue retrievedValue = (AttributeValue) this.getSession().get(AttributeValue.class, attributeValue.getId());
assertEquals("Retrieved value is not of expected class,", valueClass, retrievedValue.getClass());
assertEquals("Retrieved value is wrong,", ((AttributeValue) attributeValue).getValue(), retrievedValue.getValue());
assertEquals("Retrieved value does not have expected locale,", attributeValue.getLocale(), retrievedValue.getLocale());
}
Full stack trace of any exception that occurs:Code:
org.hibernate.exception.GenericJDBCException: could not load an entity: [com.idium.ips.attributes.baseattributetypes.AttributeValue#2]
at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:91)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:79)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.loader.Loader.loadEntity(Loader.java:1796)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:93)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:81)
at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:2729)
at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:365)
at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:346)
at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:123)
at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:177)
at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:87)
at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:809)
at org.hibernate.impl.SessionImpl.get(SessionImpl.java:749)
at org.hibernate.impl.SessionImpl.get(SessionImpl.java:742)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:271)
at $Proxy0.get(Unknown Source)
at com.idium.ips.attributes.baseattributetypes.AttributeTypesTestInSuite.doAssertions(AttributeTypesTestInSuite.java:49)
at com.idium.ips.attributes.baseattributetypes.AttributeTypesTestInSuite.testDoubleValue(AttributeTypesTestInSuite.java:30)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:40)
Caused by: java.sql.SQLException: S1000 General error java.lang.ClassCastException: java.lang.Double in statement [select attributev0_.ID as ID8_0_, attributev0_.LOCALE as LOCALE8_0_, attributev0_.VALUE as VALUE9_0_, attributev0_.VALUE as VALUE10_0_, attributev0_.VALUE as VALUE11_0_, attributev0_.clazz_ as clazz_0_ from ( select LOCALE, VALUE, ATTRIBUTE_ID, ID, 1 as clazz_ from STRINGATTRIBUTEVALUE union select LOCALE, VALUE, ATTRIBUTE_ID, ID, 2 as clazz_ from DOUBLEATTRIBUTEVALUE union select LOCALE, VALUE, ATTRIBUTE_ID, ID, 3 as clazz_ from LONGATTRIBUTEVALUE ) attributev0_ where attributev0_.ID=?]
at org.hsqldb.jdbc.Util.throwError(Unknown Source)
at org.hsqldb.jdbc.jdbcPreparedStatement.executeQuery(Unknown Source)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:137)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1676)
at org.hibernate.loader.Loader.doQuery(Loader.java:662)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:223)
at org.hibernate.loader.Loader.loadEntity(Loader.java:1782)
... 37 more
Name and version of the database you are using:HSQLDB 1.8.0.1
The generated SQL (show_sql=true):Code:
select attributev0_.ID as ID8_0_, attributev0_.LOCALE as LOCALE8_0_, attributev0_.VALUE as VALUE9_0_, attributev0_.VALUE as VALUE10_0_, attributev0_.VALUE as VALUE11_0_, attributev0_.clazz_ as clazz_0_ from ( select LOCALE, VALUE, ATTRIBUTE_ID, ID, 1 as clazz_ from STRINGATTRIBUTEVALUE union select LOCALE, VALUE, ATTRIBUTE_ID, ID, 2 as clazz_ from DOUBLEATTRIBUTEVALUE union select LOCALE, VALUE, ATTRIBUTE_ID, ID, 3 as clazz_ from LONGATTRIBUTEVALUE ) attributev0_ where attributev0_.ID=?
Debug level Hibernate log excerpt:Code:
Hibernate: insert into AttributeSet (name, ID) values (?, null)
Hibernate: call identity()
Hibernate: insert into ATTRIBUTE (ATTRIBUTESET_ID, name, ID) values (?, ?, null)
Hibernate: call identity()
Hibernate: select next value for hibernate_sequence from dual_hibernate_sequence
Hibernate: insert into DOUBLEATTRIBUTEVALUE (LOCALE, VALUE, ID) values (?, ?, ?)
Hibernate: select attributev0_.ID as ID8_0_, attributev0_.LOCALE as LOCALE8_0_, attributev0_.VALUE as VALUE9_0_, attributev0_.VALUE as VALUE10_0_, attributev0_.VALUE as VALUE11_0_, attributev0_.clazz_ as clazz_0_ from ( select LOCALE, VALUE, ATTRIBUTE_ID, ID, 1 as clazz_ from STRINGATTRIBUTEVALUE union select LOCALE, VALUE, ATTRIBUTE_ID, ID, 2 as clazz_ from DOUBLEATTRIBUTEVALUE union select LOCALE, VALUE, ATTRIBUTE_ID, ID, 3 as clazz_ from LONGATTRIBUTEVALUE ) attributev0_ where attributev0_.ID=?
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