Hi,
I'm facing a problem where 2 identical foreign keys (for the same column and table) are created by hbm2ddl task as a result of a few many-to-many relations.
I narrowed this down to 2 classes: Member and Group.
Group extends Member. Member contains a set of parent groups and Group contains a set of child groups.
Here's the code:
// Member
@Entity
@Table(name="PARENT_TABLE")
@Inheritance(strategy= InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="type",discriminatorType=DiscriminatorType.STRING)
public abstract class Member {

private String name;
private Set<Group> parentGroups;

@Id
@Column(name="NAME", length=100, nullable=false)
public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

@ManyToMany(
targetEntity= Group.class
)
@JoinTable(
name="MEMBER_TO_GROUP",
joinColumns={@JoinColumn(name="MEMBER_ID")},
inverseJoinColumns={@JoinColumn(name="GROUP_ID")}
)
public Set<Group> getParentGroups() {
return parentGroups;
}

public void setParentGroups(Set<Group> parentGroups) {
this.parentGroups = parentGroups;
}
}

// Group
@Entity
@DiscriminatorValue("group")
public class Group extends Member {

private Set<Group> childGroups;

@ManyToMany(
mappedBy="parentGroups",
targetEntity=Group.class
)
public Set<Group> getChildGroups() {
return childGroups;
}

public void setChildGroups(Set<Group> childGroups) {
this.childGroups = childGroups;
}
}

The result of this is 2 identical foreign keys:
alter table MEMBER_TO_GROUP
add constraint FK16A5E3A017C979DF
foreign key (MEMBER_ID)
references PARENT_TABLE;

alter table MEMBER_TO_GROUP
add constraint FK16A5E3A08AD6A8FA
foreign key (MEMBER_ID)
references PARENT_TABLE;

It seems to me like a bug.
Did anyone else encounter this issue?
Is there a solution for it?