休眠Session.save问题 [英] Hibernate Session.save issue

问题描述

你好我有一个域对象让我们说学生和它的卷不作为主键

这里是它的示例映射。

  @Id 
 @Column（name =Roll_NO，unique = true，nullable = false）
 @GeneratedValue（strategy = GenerationType .SEQUENCE，generator =Roll_NO_SEQ）
 @SequenceGenerator（name =Roll_NO_SEQ，sequenceName =Roll_NO_SEQ，allocationSize = 1）
 public Long getRollNo（）{
 return this.rollNo ; 
 
 $ / code> 

问题：让我们说一个特定的学生是否从数据库中删除，然后在重新入场时再次承认我想保留旧版没有。所以当我打电话给session.save时，hibernate会根据指定的Sequence指定一个新的No，而不是通过setRollNo（）方法设置。有没有办法在hibernate中实现这一点？

解决方案

鉴于您无法更改遗留代码，Ryan拥有正确的想法。前一段时间我在一个个人项目中不得不基本做同样的事情。有两个部分：简单的部分是允许有效设置另外自动编号的列ID ......另一个是当您转到Save（）时，使ID生成器停止覆盖该值。

以下是我使用的FlexibleIDGenerator的代码：

 公共类FlexibleIDGenerator扩展了IdentityGenerator实现可配置{
 public static final String DEFAULT =default; 
 
私有IdentifierGenerator assignedGenerator; 
私有标识符生成器defaultGenerator; 
 
 @SuppressWarnings（unchecked）
 public Serializable generate（SessionImplementor session，Object object）throws HibernateException {
 // boolean useDefault = false; 
 
 if（object（instance）of OverridableIdentity）{
 if（（（OverridableIdentity）object）.isIDOverridden（））{
 try {
 Class cl = object.getClass（ ）.getSuperclass（）; 
 Method [] methods = cl.getDeclaredMethods（）; （int i = 0; i< methods.length; i ++）{
 if（methods [i] .getName（）。equalsIgnoreCase（setId））{$ b（
 
） $ b methods [i] .invoke（object，Integer.valueOf（（（（OverridableIdentity）object）.getOverriddenID（））））; 
 
 $ b} catch（Exception ex）{
 ex.printStackTrace（）; 
} 
 return assignedGenerator.generate（session，object）; 
} else {
 return defaultGenerator.generate（session，object）; 
} 
} else {
 return defaultGenerator.generate（session，object）; 
 
 
 
 public void configure（Type type，Properties params，Dialect d）throws MappingException {
 assignedGenerator = IdentifierGeneratorFactory.create（assigned，type， params，d）; 
 defaultGenerator = IdentifierGeneratorFactory.create（increment，type，params，d）; 
 
 
 
 
 
 
 
为了使用它，你需要更新你的Hibernate映射文件如下：
 
 
 < id 
 name =Id
 type =integer 
 column =id
> 
< generator class =com.mypackage.FlexibleIDGenerator/> 
< / id> 
  
另一个细节：我在我的基础对象中添加了一个名为GetOverriddenID（）的方法，以避免混淆关于我是否使用正常ID（在Update（）调用中）或重写的。
 
 
 
希望有帮助。
 
Hi I have a domain object lets say Student and its Roll no as a primary key

here is the sample mapping for it.
    @Id
@Column(name = "Roll_NO", unique = true, nullable = false)
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "Roll_NO_SEQ")
@SequenceGenerator(name = "Roll_NO_SEQ", sequenceName = "Roll_NO_SEQ", allocationSize = 1)
public Long getRollNo() {
    return this.rollNo;
}
issue : lets say if a particular student was deleted from the database, and then re-admitted at the time of re-admission i want to retain the old roll no .  so when i call session.save hibernate assigns a new roll No based on the Sequence specified rather then what i am setting through setRollNo() method.  is there any way to achieve this in hibernate?
解决方案
Given that you cannot change the legacy code, Ryan has the right idea.  I had to do basically the same thing some time ago in a personal project.  There were two parts: the easy part is to allow the effective setting of an otherwise-autonumber-ed column's ID...and the other is to make the ID generator stop overwriting that value when you go to Save().

Here's the code to the FlexibleIDGenerator I used:
public class FlexibleIDGenerator extends IdentityGenerator implements Configurable {
   public static final String DEFAULT = "default";

   private IdentifierGenerator assignedGenerator;
   private IdentifierGenerator defaultGenerator;

@SuppressWarnings("unchecked")
public Serializable generate(SessionImplementor session, Object object) throws HibernateException {
      //boolean useDefault = false;

      if (object instanceof OverridableIdentity) {
          if (((OverridableIdentity) object).isIDOverridden()) {
              try {
                  Class cl = object.getClass().getSuperclass();
                  Method[] methods = cl.getDeclaredMethods();

                  for (int i = 0; i < methods.length; i++) {
                      if (methods[i].getName().equalsIgnoreCase("setId")) {
                          methods[i].invoke(object, Integer.valueOf((((OverridableIdentity) object).getOverriddenID())));
                      }
                  }
              } catch (Exception ex) {
                  ex.printStackTrace();
              }
              return assignedGenerator.generate(session, object);
          } else {
              return defaultGenerator.generate(session, object);
          }
      } else {
          return defaultGenerator.generate(session, object);
      }
   }

   public void configure(Type type, Properties params, Dialect d) throws MappingException {
      assignedGenerator = IdentifierGeneratorFactory.create("assigned", type, params, d);
      defaultGenerator = IdentifierGeneratorFactory.create("increment", type, params, d);          
   }
}
To use that for a class, you update your Hibernate mapping file like this:
        <id
        name="Id"
        type="integer"
        column="id"
    >
        <generator class="com.mypackage.FlexibleIDGenerator"/>
    </id>
One other detail: I added a method to my base object called "GetOverriddenID()" to avoid confusion about whether I'm using the "normal" ID (in Update() calls) or the overridden ones.

Hope that helps.

                        
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