Question

我正在尝试使用名为instrument and componist的实体创建一个名为muziekstuk的实体所以我创建了一个带有3个外键的连接表，用于muziekstuk乐器和组件的id。

创建了muziekstuk和乐器，我从下拉列表中选择了组件

这是行动代码：

    MuziekstukDAOImpl reg = new MuziekstukDAOImpl();
    ComponistDAOImpl com = new ComponistDAOImpl();

    int componistid = Integer.parseInt(MComponist);
    Componist componist = (Componist) com.getById(componistid);

    Instrument i1 = new Instrument(MInstrument1, Integer.parseInt(MAantal1));

    Muziekstuk muziekstuk = new Muziekstuk(MTitel,MGenre,componist,i1);
    reg.save(muziekstuk);

它确实只在连接表中制作了一个新乐器和muziekstuk，componist的id为null：S 有谁知道为什么？

以下是我的其余代码： Muziekstuk：

@Entity
@Table(name = "STUD1630651.MFMUZIEKSTUK")
public class Muziekstuk {


@Id
@GeneratedValue(strategy=GenerationType.AUTO, generator="my_entity_seq_gen")
@SequenceGenerator(name="my_entity_seq_gen", sequenceName="HIBERNATE_SEQUENCE_MUZIEKSTUK")
@Column(name = "ID")
private int id;

@Column(name = "TITEL")
private String titel;

@Column(name = "GENRE")
private String genre;

@OneToOne(cascade=CascadeType.ALL)  
@JoinTable(name="MFMUZIEKSTUKJOIN",joinColumns=
{@JoinColumn(name="MUZIEKSTUKID")},inverseJoinColumns=
{@JoinColumn(name="COMPONISTID")})
private Componist componist;

@OneToOne(cascade=CascadeType.ALL)  
@JoinTable(name="MFMUZIEKSTUKJOIN",joinColumns=
{@JoinColumn(name="MUZIEKSTUKID")},inverseJoinColumns=
{@JoinColumn(name="INSTRUMENTID")})
private Instrument instrument;


public Muziekstuk(String titel, String genre, Componist componist, Instrument instrument){
    this.titel = titel;
    this.genre = genre;
    this.componist = componist;
    this.instrument = instrument;
}

public Muziekstuk(int id, String titel, String genre, Componist componist, Instrument instrument){
    this.id = id;
    this.titel = titel;
    this.genre = genre;
    this.componist = componist;
    this.instrument = instrument;
}


//GETTERS AND SETTERS

Componist：

@Entity
@Table(name = "STUD1630651.MFCOMPONIST")  
public class Componist {

@Id
@GeneratedValue(strategy=GenerationType.AUTO, generator="my_entity_seq_gen")
@SequenceGenerator(name="my_entity_seq_gen", sequenceName="HIBERNATE_SEQUENCE_COMPONIST")
@Column(name = "ID")
private int id;

@Column(name = "NAAM")  
private String naam;

@Column(name = "LAND")  
private String land;

@Column(name = "TIJDVLAK")
private String tijdvlak;

@Column(name = "COMPOSITIES")
private String composities;


public Componist(int id, String naam, String land, String tijdvlak, String composities){
    this.id = id;
    this.naam = naam;
    this.land = land;
    this.tijdvlak = tijdvlak;
    this.composities = composities;
}

public Componist(String naam, String land, String tijdvlak, String composities){
    this.naam = naam;
    this.land = land;
    this.tijdvlak = tijdvlak;
    this.composities = composities;
}

public Componist(){
}

//GETTERS AND SETTERS

仪器：

@Entity
@Table(name = "STUD1630651.MFCOMPONIST")  
public class Componist {

@Id
@GeneratedValue(strategy=GenerationType.AUTO, generator="my_entity_seq_gen")
@SequenceGenerator(name="my_entity_seq_gen", sequenceName="HIBERNATE_SEQUENCE_COMPONIST")
@Column(name = "ID")
private int id;

@Column(name = "NAAM")  
private String naam;

@Column(name = "LAND")  
private String land;

@Column(name = "TIJDVLAK")
private String tijdvlak;

@Column(name = "COMPOSITIES")
private String composities;


public Componist(int id, String naam, String land, String tijdvlak, String composities){
    this.id = id;
    this.naam = naam;
    this.land = land;
    this.tijdvlak = tijdvlak;
    this.composities = composities;
}

public Componist(String naam, String land, String tijdvlak, String composities){
    this.naam = naam;
    this.land = land;
    this.tijdvlak = tijdvlak;
    this.composities = composities;
}

public Componist(){
}

//GETTERS AND SETTERS

在DAO中保存功能：

@Override
public void save(Object t) {
  Muziekstuk muziekstuk = (Muziekstuk) t;
  System.out.println(muziekstuk.getComponist().getId());
  Session session = null;  
  Transaction transaction = null;  
  try {  
      session = HibernateUtil.getSessionFactory().openSession();  
      transaction = session.beginTransaction(); 
      session.saveOrUpdate(muziekstuk);
      transaction.commit();   
  } catch (Exception e) {  
      if (transaction != null) {  
          transaction.rollback();
          System.out.println("exception");
          e.printStackTrace();
      }  
  } finally {  
      if (session != null) {  
          session.close();  
      }  
  }  

}

这是sql trace：

Hibernate: select componist0_.ID as ID1_2_0_, componist0_.COMPOSITIES as COMPOSIT2_2_0_, componist0_.LAND as       LAND3_2_0_, componist0_.NAAM as NAAM4_2_0_, componist0_.TIJDVLAK as TIJDVLAK5_2_0_ from STUD1630651.MFCOMPONIST componist0_ where componist0_.ID=?
Hibernate: select HIBERNATE_SEQUENCE_MUZIEKSTUK.nextval from dual
Hibernate: select HIBERNATE_SEQUENCE_INSTRUMENT.nextval from dual
Hibernate: insert into STUD1630651.MFINSTRUMENT (HOEVEELHEID, NAAM, ID) values (?, ?, ?)
Hibernate: insert into STUD1630651.MFMUZIEKSTUK (GENRE, TITEL, ID) values (?, ?, ?)
Hibernate: insert into MFMUZIEKSTUKJOIN (INSTRUMENTID, MUZIEKSTUKID) values (?, ?)

应该是3？在MUZIEKSTUKJOIN

Answer 1

事实证明，连接表只能引用1个表而不是2个，所以如果有人在想，你应该制作2个连接表。

Hibernate只保存数据库中3个值中的2个

1 个答案: