Hi everyone,
I am having troubles with mapping a map containing an array as it's value type (a simple array of string).

The only piece of information relating to my problem I could find was the following: http://osdir.com/ml/java.french.general ... 00025.html
It is in french but the person answering mainly explains that his understanding of the DTD makes him think that it's impossible to persist a map of map.

Is it true or is there a piece of information I missed in the documentation?

I don't know what to put in place of the <element> tag to be able to persist that array of string.


Hibernate version:
3.2.2
Hibernate configuration:
<!-- Auto commit transactions to the DB -->
<property name="connection.autocommit">false</property>

<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>

<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>

<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>

<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>

<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">auto</property>

Mapping documents:
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<!-- TODO find a better solution for lazy loading policy -->
<hibernate-mapping package="com.tests"
default-access="field"
default-cascade="save-update"
default-lazy="false">

<class name="TestMap$MyMap" table="mymap">
<id type="long">
<generator class="increment"/>
</id>
<map name="mMap">
<key column="MyMapId"/>
<map-key type="string"/>
<element type="string"/> <!-- there I would like to put something like type=string-array or use an <array> instead of the <element> tag-->
</map>
</class>

</hibernate-mapping>
Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:
Hibernate: select max(id) from mymap
Hibernate: insert into mymap (id) values (?)
Hibernate: insert into mMap (MyMapId, idx, elt) values (?, ?, ?)
java.lang.ClassCastException
at org.hibernate.type.StringType.toString(StringType.java:44)
at org.hibernate.type.NullableType.nullSafeToString(NullableType.java:93)
at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:140)
at org.hibernate.type.NullableType.nullSafeSet(NullableType.java:107)
at org.hibernate.persister.collection.AbstractCollectionPersister.writeElement(AbstractCollectionPersister.java:755)
at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1143)
at org.hibernate.action.CollectionRecreateAction.execute(CollectionRecreateAction.java:26)
at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:248)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:232)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:143)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
at com.tests.TestMap.testMap(TestMap.java:62)
at com.tests.TestMap.main(TestMap.java:47)


The class cast exception obviously happens because the java type is String[] and mapping file describes says it's a string since I don't know how to specify it should be an array.

No idea anyone ? No pointer, any indication ?

All I know is that the <map> tag has an inner <element> tag to indicate describe the objects stored in the map.

That <element> can also be <composit-element>, <one-to-many> or <many-to-many>.

I could achieve the persistence of the map with the composit-element tag but that forces me to write an intermediary class 'MyMapValues' containing the values in the form of the String array.

However I wouldn't like to have to write intermediary classes for all the maps of my code containing different collections as values.

I had the same problem recently, and what I did was creating a StringArray wrapper class, and using that as the element. For what I understood (I may be wrong though) there is no other way.

<element> requires that the element be a basic type (which an array is not).

<one-to-many> or <many-to-many> require that the element be an entity (a class). This is what I used, having the StringArray as an element.

<composite-element> clearly states in the documention that it cannot have collection properties, so we cannot have a <composite-element> with and <array> collection. You can map an array as a property though:
<composite-element class="com.foo.StringArray" table="FOO_STRINGS">
<property name="strings"></property>
<composite-element>

and it will serialize the array into one column, but you'll still need a StringArray wrapper class, and because you are serializing the array in a column, it may be limited in size. So because of this I didn't use this solution.

Thank you for your answer.

That's what I was afraid of, however this seems to me as non negligible constraint.
Having to wrap all the map entries to StringArrays, IntArrays ... may potentially represent a lot of work depending on the original architecture.

Hopefully I don't have too much of them for now so I can do it.
I was just hoping there would be a standard generic solution for that problem.

Thank you again.

Does anyone from hibernate care to respond to this? I am also suffering from this problem... I need to map a Set of values.