@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
public abstract class TE {
   
   @Id
   @GenericGenerator(name = "idGenerator", strategy = "assigned")
   @GeneratedValue(generator = "idGenerator")
   @Column(name="TE_KEY")
   private String id;
   
   @OneToMany
   @JoinColumn(name="TA_KEY", referencedColumnName="TE_KEY", insertable=false, updatable=false)
   private List<TA> taList;
}

public class TE1 extends TE {
}

public class TE2 extends TE {
}

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="ta_type")
public abstract class TA {
   
   @Id
   @GenericGenerator(name = "idGenerator", strategy = "assigned")
   @GeneratedValue(generator = "idGenerator")
   @Column(name="TA_KEY")
   private String id;
   
   public abstract void setTE(TE TE);

   public abstract TE getTE();
}

@Entity
@DiscriminatorValue("TE1")
public class TA2 extends TA {
   
   @ManyToOne(targetEntity=TE1.class)
   @JoinColumn(name="TE_ENTITY_FK")
   private TE TE;

   public TE getTE() {
   return TE;
   }

   public void setTE(TE TE) {
      this.TE = TE;
   }
}

@Entity
@DiscriminatorValue("TE2")
public class TA2 extends TA {
   
   @ManyToOne(targetEntity=TE2.class)
   @JoinColumn(name="TE_ENTITY_FK")
   private TE TE;

   public TE getTE() {
      return TE;
   }

   public void setTE(TE TE) {
      this.TE = TE;
   }
   
}