hibernate中對象狀態的判定是根據狀態碼進行的

以前以爲hibernate是通過id來卻分對象的狀態的,分析源碼才發現是通過狀態標識的,hibernate會自動爲你的對象添加一個狀態標識,具體如下:

protected static final int PERSISTENT = 0;
protected static final int TRANSIENT = 1;
protected static final int DETACHED = 2;
protected static final int DELETED = 3;

switch ( entityState ) {
    case DETACHED:
    entityIsDetached( event );
    return null;
    case PERSISTENT:
    return entityIsPersistent( event );
    default: //TRANSIENT or DELETED
    return entityIsTransient( event );
}

不管是save,update還是saveOrUpdate,hibernate都會調用DefaultSaveOrUpdateEventListener類的onSaveOrUpdate(......)方法,代碼如下:

SaveOrUpdateEventListener是個接口,實現類爲DefaultSaveOrUpdateEventListener
public void onSaveOrUpdate(SaveOrUpdateEvent event) {
    final SessionImplementor source = event.getSession();
    final Object object = event.getObject();//在這裏object已經攜帶有信息了,只不過id還是爲0
    final Serializable requestedId = event.getRequestedId();//這裏都爲null.這個只有調用save(Obj,id)纔有值.

    if ( requestedId != null ) {
        //assign the requested id to the proxy, *before*
        //reassociating the proxy
        if ( object instanceof HibernateProxy ) {
            ( ( HibernateProxy ) object ).getHibernateLazyInitializer().setIdentifier( requestedId );
        }
    }

    if ( reassociateIfUninitializedProxy( object, source ) ) {//執行2次,這裏都爲false
        log.trace( "reassociated uninitialized proxy" );
        // an uninitialized proxy, noop, don't even need to
        // return an id, since it is never a save()
    }
    else {
        //initialize properties of the event:初始化屬性,把
        final Object entity = source.getPersistenceContext().unproxyAndReassociate( object );
        event.setEntity( entity );
        event.setEntry( source.getPersistenceContext().getEntry( entity ) );//從session中拿出obj相關的entityentry,這個對象持有po當前的狀態
        //return the id in the event object
        event.setResultId( performSaveOrUpdate( event ) );//執行完這句後,還會再次執行onSaveOrUpdate()方法,這時,event.getObject返回的Object     的id已經有值了
    }

}

以下代碼中hibernate會從session中讀取對象的快照,如果沒有,對象的狀態就是TRANSIENT

DefaultSaveEventListener類,繼承自DefaultSaveOrUpdateEventListener
protected Serializable performSaveOrUpdate(SaveOrUpdateEvent event) {
    // this implementation is supposed to tolerate incorrect unsaved-value
    // mappings, for the purpose of backward-compatibility
    EntityEntry entry = event.getSession().getPersistenceContext().getEntry( event.getEntity() );
    //第一次執行到這裏entry爲null,第二次這裏還是null
    if ( entry!=null && entry.getStatus() != Status.DELETED ) {
    //如果在obj在session已經有對應的entityentry，即obj已經是po，且狀態是DELETED，那麼執行delete操作
        return entityIsPersistent(event);
    }
    else {
        return entityIsTransient(event);
    }
}