java JPA：检查实体对象是否已持久化
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JPA: check whether an entity object has been persisted or not
提问by Dreamer
Is there a general method that can
有没有通用的方法可以
if(entity is persisted before){
entity = entity.merge();
}else{
entity.persist();
}
So the method contain above logic is safe everywhere?
那么包含上述逻辑的方法在任何地方都是安全的？
回答by IgorMadjeric
If you need to know is object already in persistence context you should use containsmethod of EntityManager.
如果你需要知道的是对象已经在你应该使用持久化上下文contains的方法EntityManager。
Only EntityManagercan tell you is entity persisted or not, entity does not have such information.
只能EntityManager告诉你实体是否持久化，实体没有这些信息。
Here you can check javadoc for containsmethod.
在这里您可以检查 javadoc 以获取contains方法。
if (!em.contains(entity)) {
em.persist(entity);
} else {
em.merge(entity);
}
回答by Khalil
To check if entity object has been persisted or not by the current PersistenceContext you can use the EntityManager method contains(Object entity)
要检查当前 PersistenceContext 是否已持久化实体对象，您可以使用 EntityManager 方法contains(Object entity)
