java - Hibernate 仅插入数据库新记录

Question

我正在尝试将一些对象写入数据库，我编写了以下工作正常的代码，但问题是因为我正在使用 while 循环，hibernate 将每个对象都视为一个新记录，这导致数据库填充已经存在的值

我的问题是，我可以使用哪种注解或技术只将新记录(新对象的值)写入数据库，而无需再次写入相同的对象，以防它之前被写入(仅在不存在时插入)

这是我的代码

public class Parser {
  public static void logParser() throws IOException {
    // Creating the configuration object
    Configuration cfg = new Configuration();
    cfg.configure("hibernate.cfg.xml");
    // Ccreating the session factory object
    SessionFactory factory = cfg.buildSessionFactory();
    String fileName = "example.txt";
    File logfile = new File("fileName");
    Scanner scanner = new Scanner(new File(fileName), "UTF-8");
    while (scanner.hasNext()) {
      String s = scanner.nextLine();
      if (s.startsWith("Start")) {
        String[] logArray = s.split("\\|"); 
         System.out.println(Arrays.toString(logArray));
        // here is the session object
        Session session = factory.openSession();
        // transaction
        Transaction t = session.beginTransaction();
        // here is where the object is being written into the DB
        NetGroup ng = new NetGroup();
        ng.setNetGroup(logArray[2]);
        session.persist(ng);
        session.saveOrUpdate(ng);
        t.commit();
        session.close();
        System.out.println("Successfully created an object and wrote its values into database ");
        System.out.println();
      }
    }
    scanner.close();
    System.out.println("Successfully updated the Data Base");
  }
  }

Answer 1

你的问题发生是因为在每个循环中你创建一个新实体并持久化它，然后你提交并关闭 session ，所以当在第二个循环中开始一个新事务时，已经持久化的实体和第二个实体之间没有引用，因此将创建新实体。

您需要重新找到您的实体，然后更新它(如果存在)，否则创建新实体并保留它。

该代码将解决您的问题

 public class Parser {
    public static void logParser() throws IOException {
        // Creating the configuration object
        Configuration cfg = new Configuration();
        cfg.configure("hibernate.cfg.xml");
        // Ccreating the session factory object
        SessionFactory factory = cfg.buildSessionFactory();
        String logFileName = "example.txt";
        File logfile = new File("fileName");
        Scanner scanner = new Scanner(new File(fileName), "UTF-8");
        // here is the session object
        Session session = factory.openSession();
        // transaction
        Transaction t = session.beginTransaction();

        while (scanner.hasNext()) {
            String s = scanner.nextLine();
            if (s.startsWith("Start")) {
                String[] logArray = s.split("\\|");
                System.out.println(Arrays.toString(logArray));
                Query query = session.createQuery("FROM " + getTableName() + " Where  your condition "); // use unique filed 
                List<NetGroup> list = query.list();
                if(list.size()==0){
                    NetGroup ng =new NetGroup();
                }else{
                    ng =list.get(0);
                }
               ng.setNetGroup(logArray[2]);

                session.saveOrUpdate(ng);
                System.out.println("Successfully created an object and wrote its values into database ");
                System.out.println();
            }
        }
        session.close();
        t.commit();
        scanner.close();
        System.out.println("Successfully updated the Data Base");
    }
}

确保输入有效条件而不是“您的条件”