blocks|key|406525|text|ID仅保证在刷新时生成。持久化实体只会使其“附加”到持久化上下文。所以，要么显式地刷新实体管理器：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|406526|em.persist(abc);
em.flush();
return+abc.getId();|code-block|syntax|javascript|406527|或者返回实体本身而不是其ID。当事务结束时，将发生刷新，因此事务之外的实体的用户将在实体中看到生成的ID。|406528|@Override
public+ABC+addNewABC(ABC+abc)+{
++++abcDao.insertABC(abc);
++++return+abc;
}|406529|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

The ID is only guaranteed to be generated at flush time. Persisting an entity only makes it "attached" to the persistence context. So, either flush the entity manager explicitely:

<pre><code>em.persist(abc);
em.flush();
return abc.getId();
</code></pre>

or return the entity itself rather than its ID. When the transaction ends, the flush will happen, and users of the entity outside of the transaction will thus see the generated ID in the entity.

<pre><code>@Override
public ABC addNewABC(ABC abc) {
 abcDao.insertABC(abc);
 return abc;
}
</code></pre>

blocks|key|622160|text|em.persist(abc);
em.refresh(abc);
return+abc;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|622161|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>em.persist(abc);
em.refresh(abc);
return abc;
</code></pre>

blocks|key|406608|text|您还可以使用GenerationType.TABLE而不是IDENTITY，后者仅在插入后可用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|406609|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You could also use GenerationType.TABLE instead of IDENTITY which is only available after the insert.

blocks|key|622239|text|我是这样做的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|622240|EntityManager+entityManager+=+getEntityManager();
EntityTransaction+transaction+=+entityManager.getTransaction();
transaction.begin();
entityManager.persist(object);
transaction.commit();
long+id+=+object.getId();
entityManager.close();|code-block|syntax|javascript|622241|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is how I did it:

<pre><code>EntityManager entityManager = getEntityManager();
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();
entityManager.persist(object);
transaction.commit();
long id = object.getId();
entityManager.close();
</code></pre>

blocks|key|622303|text|@Entity
public+class+ABC+implements+Serializable+{
+++++@Id
+++++@GeneratedValue(strategy=GenerationType.IDENTITY)
+++++private+int+id;+++
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|622304|检查@GeneratedValue表示法在您的实体中是否存在class.This告诉JPA您的实体属性自动生成的行为|unstyled|622305|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>@Entity
public class ABC implements Serializable {
 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)
 private int id; 
}
</code></pre>

check that @GeneratedValue notation is there in your entity class.This tells JPA about your entity property auto-generated behavior

blocks|key|406722|text|另一个兼容4.0的选项：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|406723|在提交更改之前，您可以从与上下文关联的集合中恢复新的CayenneDataObject对象，如下所示：|offset|length|style|CODE|406724|CayenneDataObject+dataObjectsCollection+=+(CayenneDataObject)cayenneContext.newObjects();|code-block|syntax|javascript|406725|然后访问集合中每个元素的ObjectId，如下所示：|406726|ObjectId+objectId+=+dataObject.getObjectId();|406727|最后，您可以迭代这些值，其中通常生成的-id将是getIdSnapshot()返回的映射中的第一个值(对于单个列键)，它还包含与PK关联的列名作为键：|406728|objectId.getIdSnapshot().values()|406729|entityMap^0|0|Q|H|0|0|C|8|0|0|O|F|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@$D|Y|E|Z|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|10|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|11|8|@$D|12|E|13|F|G]]|9|@]|A|$]]|$1|O|3|P|5|J|7|14|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|15|8|@$D|16|E|17|F|G]]|9|@]|A|$]]|$1|S|3|T|5|J|7|18|8|@]|9|@]|A|$K|L]]|$1|U|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|V|$]]

Another option compatible to 4.0:

Before committing the changes, you can recover the new <code>CayenneDataObject</code> object(s) from the collection associated to the context, like this:

<pre><code>CayenneDataObject dataObjectsCollection = (CayenneDataObject)cayenneContext.newObjects();
</code></pre>

then access the <code>ObjectId</code> for each one in the collection, like:

<pre><code>ObjectId objectId = dataObject.getObjectId();
</code></pre>

Finally you can iterate under the values, where usually the generated-id is going to be the first one of the values (for a single column key) in the Map returned by <code>getIdSnapshot()</code>, it contains also the column name(s) associated to the PK as key(s):

<pre><code>objectId.getIdSnapshot().values()
</code></pre>

blocks|key|622380|text|我就是这么做的。你可以试试|type|unstyled|depth|inlineStyleRanges|entityRanges|data|622381|++++public+class+ABCService+{
++++@Resource(name="ABCDao")
++++ABCDao+abcDao;

++++public+int+addNewABC(ABC+abc)+{
+++++++++ABC.setId(0);
+++++++++return+abcDao.insertABC(abc);
++++}
}|code-block|syntax|javascript|622382|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

This is how I did it. You can try

<pre><code> public class ABCService {
 @Resource(name="ABCDao")
 ABCDao abcDao;

 public int addNewABC(ABC abc) {
 ABC.setId(0);
 return abcDao.insertABC(abc);
 }
}
</code></pre>

I'm using JPA (EclipseLink) and Spring. Say I have a simple entity with an auto-generated ID:

<pre><code>@Entity
public class ABC implements Serializable {
 @Id
 @GeneratedValue(strategy=GenerationType.IDENTITY)
 private int id;

 // ...
}
</code></pre>

In my DAO class, I have an insert method that calls <code>persist()</code> on this entity. I want the method to return the generated ID for the new entity, but when I test it, it returns <code>0</code> instead.

<pre><code>public class ABCDao {
 @PersistenceContext
 EntityManager em;

 @Transactional(readOnly=false)
 public int insertABC(ABC abc) {
 em.persist(abc);
 // I WANT TO RETURN THE AUTO-GENERATED ID OF abc
 // HOW CAN I DO IT?
 return abc.id; // ???
 }
}
</code></pre>

I also have a service class that wraps the DAO, if that makes a difference:

<pre><code>public class ABCService {
 @Resource(name="ABCDao")
 ABCDao abcDao;

 public int addNewABC(ABC abc) {
 return abcDao.insertABC(abc);
 }
}
</code></pre>

JPA - Returning an auto generated id after persist()

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我使用的是JPA (EclipseLink)和Spring。假设我有一个简单的实体，它有一个自动生成的ID：@Entitypublic class ABC implements Serializable {     @Id     @GeneratedValue(strategy=GenerationType.IDEN...

问JPA -在persist()之后返回一个自动生成的id
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