JPA: Composite key mapping with common field as primary key - jpa

Question

I have two table with composite keys which shares a common column as part of their composite key. Below is by ER:
Table A: schemaId,aID
Table B: schemaId,bID,aID
Here scheId is contant value.
A and B has OneToMany relation(i.e., A record has multiple B records)
When I form a ManyToOne relation in Table B, I am doing below:
#ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
#JoinColumn(name = "aID", referencedColumnName = "aID")
#JoinColumn(name = "schemaId", referencedColumnName = "schemaId")
private A a;
Above works fine(records get inserted), but I require schemaId as part of Entity B as there are other table which share this composite key from Table B.
In order to maintain the filed in entity if I change #JoinColumn with (insert="false" update="false"), value is passing as null for schemaId as it will treat as optional one.
Entity A:
#IdClass(APK.class)
#Entity
public class A
{
#Id
private Integer schemaId;
#Id
private Integer aId;
#OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "a")
private List<B> blist;
...
}
public class APK implements Serializable{
private Integer schemaId;
private Integer aId;
}
Entity B:
#IdClass(BPK.class)
#Entity
public class B
{
#Id
private Integer schemaId;
#Id
private Integer bId;
private Integer aId;
#ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
#JoinColumn(name = "aID", referencedColumnName = "aID")
#JoinColumn(name = "schemaId", referencedColumnName = "schemaId")
private A a;
}
public class APK implements Serializable{
private Integer schemaId;
private Integer bId;
}