persist

JPA EntityManager：为什么在merge（）上使用persist（）？

由 末鹿安然 提交于 2019-12-15 18:11:32
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> EntityManager.merge() 可以插入新对象并更新现有对象。 为什么要使用 persist() （只能创建新对象）？ #1楼 无论哪种方式都会将实体添加到PersistenceContext中，区别在于您之后对实体执行的操作。 Persist接受实体实例，将其添加到上下文并使该实例得到管理（即将跟踪对该实体的未来更新）。 合并创建实体的新实例，从提供的实体复制状态，并管理新副本。 您传入的实例将不会被管理（您所做的任何更改都不会成为交易的一部分 - 除非您再次调用合并）。 也许代码示例会有所帮助。 MyEntity e = new MyEntity(); // scenario 1 // tran starts em.persist(e); e.setSomeField(someValue); // tran ends, and the row for someField is updated in the database // scenario 2 // tran starts e = new MyEntity(); em.merge(e); e.setSomeField(anotherValue); // tran ends but the row for someField is not

Spark中的checkpoint作用与用法

由 六月ゝ 毕业季﹏ 提交于 2019-12-14 23:24:09
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> checkpoint的意思就是建立检查点,类似于快照,例如在spark计算里面 计算流程DAG特别长,服务器需要将整个DAG计算完成得出结果,但是如果在这很长的计算流程中突然中间算出的数据丢失了,spark又会根据RDD的依赖关系从头到尾计算一遍,这样子就很费性能,当然我们可以将中间的计算结果通过cache或者persist放到内存或者磁盘中,但是这样也不能保证数据完全不会丢失,存储的这个内存出问题了或者磁盘坏了,也会导致spark从头再根据RDD计算一遍,所以就有了checkpoint,其中checkpoint的作用就是将DAG中比较重要的中间数据做一个检查点将结果存储到一个高可用的地方(通常这个地方就是HDFS里面) 一般我们先进行cache然后做checkpoint就会只走一次流程,checkpoint的时候就会从刚cache到内存中取数据写入hdfs中 其中作者也说明了,在checkpoint的时候强烈建议先进行cache,并且当你checkpoint执行成功了,那么前面所有的RDD依赖都会被销毁 来源： oschina 链接： https://my.oschina.net/u/660188/blog/1838692

spark 中cache 和persist 区别与用法 欢迎指正

由 风流意气都作罢 提交于 2019-12-14 23:20:48
【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 网上一大把资源来介绍cache的好处优点，但有的时候偏偏就是会溢出，那么来说说‘同父异母’的方法persist的使用吧 ，完美的解决了cache内存溢出的尴尬。 两者都是持久化Rdd的方式，但是persist方法是包含cache方法的： 在persist的持久化方法有很多种组和 MEMORU_ONLY 指的就是cache 参数代表的含义分别是：是否使用磁盘缓存、是否使用内存、是否使用对外内存、是否使用反序列化 DISK_ONLY：全部用磁盘缓存（一般你的需要持久化的RDD或者DF等特别大的时候可以用这种） DISK_ONLY_2：和上边这个类似就是多了最后一个参数，表示每个分区在两个节点上创建副本 MEMORY_AND_DISK：使用磁盘加内存 （一般不是特别大的需求的时候比较推荐，最起码内存满了会自动写磁盘 ） 最后几个带_SER:的就是用java对象的方式进行存储，相比于前几种的同类型存储来说就是速度快了，但是更吃cpu 不管那个方法用完记得释放：unpersist（）！！！！ 举例调用代码： //持久化防治溢出 调用persist方法 里面要传入相应的缓存等级，这里使用的是内存加磁盘 Dataset<Row> goodsSpecPersist = goodsSpec.persist

JPA ManyToMany persist

由 主宰稳场 提交于 2019-12-14 03:07:20
问题 I have a NOTIFICATION table who contains one ManyToMany association : @Entity @Table(name="NOTIFICATION") @NamedQuery(name="Notification.findAll", query="SELECT f FROM Notification f") public class Notification { /** SOME COLUMN DEFINITION NOT IMPORTANT FOR MY CASE COD, DATE, ID_THEME, ID_TYP, IC_ARCH, ID_CLIENT, INFOS, NAME, TITRE_NOT, ID_NOT **/ @ManyToMany @JoinTable( name="PJ_PAR_NOTIF" , joinColumns={ @JoinColumn(name="ID_NOTIF") } , inverseJoinColumns={ @JoinColumn(name="ID_PJ_GEN") } )

Spring transactional context doesn't persist data

由 醉酒当歌 提交于 2019-12-13 12:27:24
问题 I know that my problem is a common problem, but I've checked a lot of questions here, checked Spring documentation and I really don't know what I am doing wrong. My problem: I've got a Spring WebFlow project using JPA (implementation: OpenJPA + MySQL database). I use Spring ORM to inject EntityManager (by @PersistenceContext annotation) to my simple RegisterDAO. I have configured GlassFishs (which I am using) connection pools for using MySQL and everything works - I can work with my database,

keep checkboxes checked after page refresh

由 走远了吗. 提交于 2019-12-12 14:58:53
问题 I have a couple of checkboxes. when any of them are clickd/checked and the search button is clicked, will grab their values and pass to the url as querystring and refresh the page returning results matching the passed query values. like this: mysite.com/result.aspx?k="Hospital" OR "Office" OR "Emergency" I am able to grab the values after 'k='. I have "Hospital" OR "Office" OR "Emergency" captured and stored in a variable. Now I need to reset the checked state of checkboxes based on these

Winforms/C#: Store/Retrieve (Persist) Content of TextBoxes between 2 Runs

由 六月ゝ 毕业季﹏ 提交于 2019-12-12 13:28:33
问题 Is there an easiest way to simply tell Winforms (mainly TextBoxes) to persist all its content e. g. to a file without me having to loop through all the controls? I saw this in a WPF application, but am clueless (also, Google did not turn up anything) whether there is an out-of-the-box, easiest approach. Again, looping through each control would be possible but seems.. too much work? Would serialization maybe work? 回答1: You can set your ApplicationSettings PropertyBinding in the Form Designer,

Doctrine2 - Get entity ID before flush

由 ぃ、小莉子 提交于 2019-12-12 08:19:53
问题 Is there any way to get an entity ID before the persist/flush? I mean: $entity = new PointData(); $form = $this->createForm(new PointDataType(), $entity); If I try $entity->getId() at this point, it returns nothing. I can get it working by: $em->persist($entity); $em->flush(); (supposing $em = $this->getDoctrine()->getEntityManager(); ) How can I achieve this? 回答1: If you want to know the ID of an entity before it's been persisted to the database, then you obviously can't use generated

Lagom: Asynchronous Operations in Command Handlers

由 老子叫甜甜 提交于 2019-12-12 05:24:53
问题 In Lagom, what do you do when a command handler must perform some asynchronous operations? For example: override def behavior = Actions().onCommand[MyCommand, Done] { case (cmd, ctx, state) => // some complex code that performs asynchronous operations // (for example, querying other persistent entities or the read-side // by making calls that return Future[...] and composing those), // as summarized in a placeholder below: val events: Future[Seq[Event]] = ??? events map { xs => ctx

How can we retain a simple State Array across Configuration changes using Headless Fragments?

由 心不动则不痛 提交于 2019-12-11 23:10:09
问题 I have gone through so many other similar questions but none solve my problem. One of the uses of Fragments (apparently) is to persist a state. I have a State array called arrState that I have wrapped in a headless fragment called StateFragment. public class StateFragment extends Fragment { public static ArrayList<Character> arrState; protected ActMainGame mActivity = null; private Character crtX; public static final String TAG = "StateFragment"; @Override public void onAttach(Activity
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