Question

我正在使用EclipeLink（JPA），并且试图解析一个Docoment以频繁地导入包含的数据。我们的软件体系结构的构建方式是，我将获得代表对象树的根元素列表，并且这些元素可能已经在数据库中可用，因为它们可以不带父项而存在！

我的DataModel看起来像这样：

@Entity
@Table(name = "studiengang")
public class Studiengang
{
   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   @Column(name = "id", length = 5)
   private int id;

   @Column(name = "name", length = 50, nullable = false, unique = true)
   private String name;

   @ManyToMany(mappedBy = "studiengaenge", fetch = FetchType.EAGER, cascade = CascadeType.MERGE)
   private Set<Vorlesung> vorlesungen;
   //getter + setter
}



@Entity
@Table(name = "vorlesung")
public class Vorlesung
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", length = 5)
    private int id;

    @Column(name = "name", length = 50, nullable = false, unique = true)
    private String name;

    @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.MERGE)
    private Set<Studiengang> studiengaenge;

    @ManyToMany(mappedBy = "vorlesungen", fetch = FetchType.EAGER, cascade = CascadeType.MERGE)
    private Set<KfzKennzeichen> kennzeichen;

    @OneToMany(mappedBy = "vorlesung", fetch = FetchType.EAGER, cascade = CascadeType.MERGE)
    private Set<Veranstaltung> veranstaltungen;
}




@Entity
@Table(name = "veranstaltung", uniqueConstraints = {
    @UniqueConstraint(columnNames = { "von", "bis", "vorlesung" })
})
public class Veranstaltung
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", length = 5)
    private int id;

    @ManyToOne(fetch = FetchType.EAGER, optional = false, cascade = CascadeType.MERGE)
    private Vorlesung vorlesung;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(nullable = false)
    private Date von;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(nullable = false)
    private Date bis;

    @ManyToOne(fetch = FetchType.EAGER, optional = false, cascade = CascadeType.MERGE)
    private Raum veranstaltungsOrt;
 }



 @Entity
 @Table(name = "raum")
 public class Raum
 {
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     @Column(name = "id", length = 5)
     private int id;

     @Column(name = "name", length = 15, nullable = false, unique = true)
     private String name;

     @OneToMany(mappedBy = "veranstaltungsOrt", fetch = FetchType.EAGER)
     private Set<Veranstaltung> veranstaltungen;
 }

我现在得到的是一个Studiengang类型的列表，我想（最好）轻松地保留它。如您所见，我已经尝试将所有内容标记为Cascade Merge，但这并没有帮助。

我最喜欢的方法是只正确配置一些实体，然后调用：

public void importiereVorlesungen(List<Studiengang> studiengaenge)
{
    for (Studiengang studiengang : studiengaenge)
    {
        persistiereEntitaet(studiengang);
    }
}

private <T> T persistiereEntitaet(T entitaet)
{
    T dbEntitaet;
    em.getTransaction().begin();
    dbEntitaet = em.merge(entitaet);
    em.getTransaction().commit();

    return dbEntitaet;
}

但这暂时不起作用。尽管我合并了实体，但出现了错误：

原因：java.sql.SQLIntegrityConstraintViolationException：键“名称”的条目“ S 1”重复在com.mysql.cj.jdbc.exceptions.SQLError.createSQLException（SQLError.java:115）在com.mysql.cj.jdbc.exceptions.SQLError.createSQLException（SQLError.java:95）在com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException（SQLExceptionsMapping.java:122）在com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal（ClientPreparedStatement.java:960）在com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal（ClientPreparedStatement.java:1116）在com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal（ClientPreparedStatement.java:1066）在com.mysql.cj.jdbc.ClientPreparedStatement.executeLargeUpdate（ClientPreparedStatement.java:1396）在com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdate（ClientPreparedStatement.java:1051）在org.eclipse.persistence.internal.databaseaccess.DatabaseAccessor.executeDirectNoSelect（DatabaseAccessor.java:890） ...还有74个

即使我尝试这样做，也会收到相同的错误：

for (Studiengang studiengang : studiengaenge)
{ 
    for (Vorlesung vorlesung : studiengang.getVorlesungen())
    {
        for (Veranstaltung veranstaltung : vorlesung.getVeranstaltungen())
        {
            Raum dbRaum;
            try
                {
                    dbRaum = persistiereEntitaet(veranstaltung.getVeranstaltungsOrt());
                }
                catch (Exception e)
                {
                    dbRaum = sucheRaum(veranstaltung.getVeranstaltungsOrt().getName());
                }
                veranstaltung.setVeranstaltungsOrt(dbRaum);
                persistiereEntitaet(veranstaltung);
            }
            try
            {
                persistiereEntitaet(vorlesung);
            }
            catch (DatabaseException e)
            {
                //Skip
            }
        }
        em.getTransaction().begin();
        em.persist(studiengang);
        em.getTransaction().commit();
        }
    }
}

当行“ persistiereEntitaet（veranstaltung）;”时到达后，将引发错误。

如何使用现有对象持久化对象树

0 个答案: