@Entity
public class A {
    @Id
    @Column(name = "a_id")
    private Long id;

    @OneToMany(mappedBy = "a", fetch = FetchType.LAZY)
    private List<B> bs;

    @OneToMany(mappedBy = "a", fetch = FetchType.LAZY)
    private List<C> cs;

    public Long getId() {return id;}
    public void setId(Long id) {this.id = id;}
    public List<B> getBs() {return bs;}
    public void setBs(List<B> bs) {this.bs = bs;}
    public List<C> getCs() {return cs;}
    public void setCs(List<C> cs) {this.cs = cs;}
}

@Entity
public class B {
    @Id
    @Column(name = "b_id")
    private Long id;

    @Column(name = "b_value")
    private String value;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "a_id")
    private A a;

    public Long getId() {return id;}
    public void setId(Long id) {this.id = id;}
    public String getValue() {return value;}
    public void setValue(String value) {this.value = value;}
    public A getA() {return a;}
    public void setA(A a) {this.a = a;}
}

@Entity
public class C {
    @Id
    @Column(name = "c_id")
    private Long id;

    @Column(name = "c_value")
    private String value;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "a_id")
    private A a;

    public Long getId() {return id;}
    public void setId(Long id) {this.id = id;}
    public String getValue() {return value;}
    public void setValue(String value) {this.value = value;}
    public A getA() {return a;}
    public void setA(A a) {this.a = a;}
}