Question on persisting entity with Bidirectional #ManyToOne relationship using Mapstruct - spring

Question

This is my first time implementing #ManyToOne relationship using JPA/Mapstruct/Spring boot. I am running into the below exception: (NOTE: Using generic names as I am unable to share all the details)
java.sql.SQLIntegrityConstraintViolationException: Column 'A_ID' cannot be null for class B when I try to persist A.
Below are the relevant details. Can you help me understand what is the mistake I am making here? I have spent few hours debugging this and reading the posts without success yet.
#Mapper(componentModel="spring", uses= {BMapper.class}, collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED)
public interface AMapper {
#Mapping(target = "aId", source="id")
#Mapping(target = "aName", source = "name")
ADTO toDTO(final A a);
#Mapping(target = "id", ignore=true)
#Mapping(target = "name", source = "aName")
A toEntity(final ADTO aDTO);
#AfterMapping
default void setBSet(A a, #MappingTarget aDTO dto) {
for(B b : a.getBs())
b.setA(a);
}
}
#Mapper(componentModel="spring", uses= {CMapper.class}, injectionStrategy = InjectionStrategy.CONSTRUCTOR )
public interface BMapper {
#Mapping(target = "bId", source="id")
#Mapping(target = "aName", ignore=true)
BDTO toDTO(final B b);
#Mapping(target = "id", ignore=true)
#Mapping(target = "a", ignore=true)
B toEntity(final BDTO bDTO);
Set<B> bDtoToBSetEntity(Set<BDTO> set);
Set<BDTO> bSetEntityToBDto(Set<B> set);
}
Below are the class definitions of ADTO and BDTO
public class ADTO implements Serializable {
private static final long serialVersionUID = 8307772637314390585L;
private Long aId;
private String aName;
private LocalDate startDate;
private LocalDate endDate;
private Set<BDTO> bs = new HashSet<>();
// Getters / Setters here
public void addToBs(BDTO b) {
if(b != null) {
bs.add(b);
}
}
// hashCode/equals/toString methods here...
}
public class BDTO implements Serializable {
private static final long serialVersionUID = 2562084231749296452L;
private Long bId;
private String name;
private LocalDate startDate;
private LocalDate endDate;
private String aName;
// getters / setters go here..
// hashCode/equals/toString methods here...
}
Below are the class definitions of entity classes, particularly pay attention to class B where the exception is related to.
#Entity
#Table(name = "TABLEB", uniqueConstraints = {
#UniqueConstraint(columnNames = "ID")})
public class B implements Serializable {
private static final long serialVersionUID = 1407209531508355406L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "ID", unique = true, nullable = false)
private Long id;
#Enumerated(EnumType.STRING)
#Column(name = "NAME", nullable = false)
private String name;
#ManyToOne(fetch = FetchType.EAGER)
#JoinColumn(name = "A_ID", referencedColumnName="ID")
private A a;
#Column(name = "START_DATE", unique = false, nullable = false)
private LocalDate startDate;
#Column(name = "END_DATE", unique = false, nullable = false)
private LocalDate endDate;
}
#Entity
#Table(name = "TABLEA", uniqueConstraints = {
#UniqueConstraint(columnNames = "ID")})
public class A implements Serializable {
private static final long serialVersionUID = 6926335188960198569L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "ID", unique = true, nullable = false)
private Long id;
#Column(name = "NAME", unique = false, nullable = false, length = 100)
private String name;
#OneToMany(mappedBy="a"/*, fetch = FetchType.EAGER*/, cascade = {CascadeType.ALL})
private Set<B> bs = new HashSet<>();
#Column(name = "START_DATE", unique = false, nullable = false)
private LocalDate startDate;
#Column(name = "END_DATE", unique = false, nullable = false)
private LocalDate endDate;
}
I am just calling save method of ADao class that persists using entity Manager.