How to persist a Map<String, List<Object>> in Hibernate

Question

I've got a Map containing MyObject instances. The MyObject class uses JPA to persist its fields:

@OneToMany(cascade = CascadeType.ALL)
@LazyCollection(LazyCollectionOption.FALSE)
private Map<String, MyObject> results = new HashMap<String, MyObject>();

We changed the value stored by the Map to a List:

private Map<String, List<MyObject>> results = new HashMap<String, List<MyObject>>();

But upon launching we receive a stack trace:

Caused by: org.hibernate.AnnotationException: Use of @OneToMany or @ManyToMany targeting an unmapped class: com.me.myapp.MyObject.results[java.util.List]
    at org.hibernate.cfg.annotations.CollectionBinder.bindManyToManySecondPass(CollectionBinder.java:1150)
    at org.hibernate.cfg.annotations.CollectionBinder.bindStarToManySecondPass(CollectionBinder.java:680)
    at org.hibernate.cfg.annotations.MapBinder$1.secondPass(MapBinder.java:107)
    at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:66)
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1221)
    at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:383)
    at org.hibernate.cfg.Configuration.buildMappings(Configuration.java:1206)
    at org.springframework.orm.hibernate3.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:673)
    at org.springframework.orm.hibernate3.AbstractSessionFactoryBean.afterPropertiesSet(AbstractSessionFactoryBean.java:211)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1368)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1334)
    ... 30 more

Does Hibernate not support persisting a Map containing (as values) List types? Or are my annotations incorrect? I haven't found this particular configuration in any of the documentation or examples.

Answer 1

The objects stored in the map must be the target object of the oneToMany association (always mapped). You can't store arbitrary objects or collections there.

Answer 2

Personally, I don't think this is a good use of Hibernate. There's no abstraction here. It would make sense if you had a model object with a one-to-many relation expressed as a child List as a data member in the parent.

My advice? Don't use Hibernate. Use straight JDBC, Spring's JDBC template, or something like iBatis.

ORM stands for "Object Relational Mapping". You have tables, so you've got the relational part. You've got data that you can assign to columns in tables.

But it sounds to me like you've got no Objects. So why use Hibernate?