Hi
I wish to map some custom attributes of an entity, stored in a Map<String,String>.

The entity is Customer and the map property is customAttributes. They should be stored in a second table:

customerid INTEGER,
name VARCHAR,
value VARCHAR,
Primary Key (customerid, name)

Is this possible with Hibernate Annotations Extentions or do I have to define a second Entity for the customAttributes?

I tried with a second Entity, but I cannot get it to work:

@Entity
public class Customer {
private Long id;
private String lastName;
private Map<String, CustomAttribute> customAttributes;

@OneToMany (cascade=CascadeType.ALL)
@JoinColumn (name="customer_id")
@MapKey (name="name")
public Map<String,CustomAttribute> getCustomAttributes() {
return customAttributes;
}
...
}

@Entity
public class CustomAttribute {
private String name;
private String value;

@Id
public String getName() {
return name;
}

...
}


I get an
IllegalArgumentException occurred calling getter of CustomAttribute.name
caused by:
java.lang.IllegalArgumentException: object is not an instance of declaring class

The second thing is that I don't know how to define the @Id in a correct way (should be composite). I would prefer a simple value mapping without the need for a second entity...

Thanks a lot.

I resolved that problem. The solution was to use @CollectionOfElements:

@CollectionOfElements (fetch=FetchType.EAGER)
@JoinTable(name="customattribute", joinColumns = @JoinColumn(name="customer_id"))
@MapKey (columns=@Column(name="name"))
@Column(name="value", nullable=true)
public Map<String,String> getCustomAttributes() {
return customAttributes;
}

No child entity is needed now.

I am posting it here because I found it quite hard to extract this from the manual, as there is no Map example for that case. Maybe it will be useful for someone.