I have the following mapping:

{{
<properties name="uniqueCode" unique="true">
<property name="code">
<column name="code" sql-type="varchar(255)" not-null="true" />
</property>
<many-to-one name="root" not-null="false" foreign-key="FKAccountChart" lazy="false" />
</properties>
}}
that used to generate the following constraint:

{{
alter table acct add constraint UK_fxplc01ecyoe1sjdrxe6yp2ne unique (root, code);`
}}

after upgrading Hibernate, it now generates:

{{
alter table acct add constraint UK_fxplc01ecyoe1sjdrxe6yp2ne unique (code);
}}