如何在hibernate中保存外键？

@Entity
@Table(name = "main_table")
public class MainTable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    // other fields and getters/setters
}

@Entity
@Table(name = "sub_table")
public class SubTable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "main_table_id")
    private MainTable mainTable;

    // other fields and getters/setters
}

MainTable mainTable = new MainTable();
// set main table fields

SubTable subTable = new SubTable();
subTable.setMainTable(mainTable);
// set sub table fields

session.save(mainTable);
session.save(subTable);

MainTable mainTable = session.get(MainTable.class, mainTableId);
Set<SubTable> subTables = mainTable.getSubTables();