I try to map a map with key and value as value types, both using a converter (see below).
Hibernate 4.3.7 does not accept attributeName = "key" but requires it to be "key.<something>" (same for the value). Is this a bug?
If I use attributeName = "key.accountId" and attributeName = "value.campaignId" Hibernate tries to map the a value as a serializable type, which is wrong. Am I doing something wrong?

Is it possible that Hibernate simply does not implement this case? The implementation in CollectionPropertyHolder seems to be a bit empty... Isn't Hibernate JPA 2.1 compliant yet?

@Converts({
@Convert(attributeName = "key", converter = AccountIdConverter.class),
@Convert(attributeName = "value", converter = CampaignIdConverter.class)
})
@ElementCollection(fetch = FetchType.EAGER)
@Fetch(FetchMode.SELECT)
@CollectionTable(name = "cluster_campaign", joinColumns=@JoinColumn(name="cluster_id"))
@MapKeyColumn(name = "account_id", nullable = false)
@Column(name = "campaign_id", nullable = false)
private Map<AccountId, CampaignId> campaignIds = Maps.newHashMap();

Hibernate lacks the implementation of this feature. I provided a patch to add this functionality, so hopefully in the near future this will work.