jsf数据表优化计数查询

Question

我有一个 JSF 数据表并显示一个包含延迟加载图像的实体。点击行查看详情后加载。

但我必须在数据表中显示图像计数。数据表使用分页，每页显示 15 行。

我使用以下注解进行映射

    // Fetch type must be lazy due to out of memory error in eager mode
@OneToMany(cascade = { CascadeType.REMOVE, CascadeType.MERGE }, mappedBy = "alarm", fetch = FetchType.LAZY, orphanRemoval = true)
@OrderBy("unixtime ASC")
@LazyCollection(LazyCollectionOption.EXTRA) // allows .size() and .contains() without initializing the whole collection
private volatile Set<AlarmImage> alarmImages = new HashSet<AlarmImage>();

用这种方法获取图片数量

 /**
 * @return the number of alarm images in this alarm
 */
public Integer getCountAlarmImages() {
    // wont initalize whole collection because LazyCollectionOption.EXTRA
    return this.alarmImages.size();
}

这是休眠日志

[2016-10-07 08:51:13,095] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,190] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,282] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,375] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,466] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,559] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,651] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,744] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,836] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:13,930] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:14,022] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:14,117] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:14,210] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:14,302] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?
[2016-10-07 08:51:14,395] [WebContainer : 1] DEBUG org.hibernate.SQL [] logStatement - select count(ID) from ALARM_IMAGE where ALARM_FK =?

我的问题是分页平均需要 1.5 秒才能加载，是否可以对此进行优化？也许并行加载每个警报的图像数量？这在 jsf 数据表中可以吗？

编辑：

休眠版本：4.2.17.Final

xhtml 文件中的行定义

<p:column>
    <h:outputText value="#{alarm.countAlarmImages}" />
</p:column>

Answer 1

不要认为有可能“并行加载”这些，它可能已经在这样做了，但我确实有一些想法给你：

1。 使用@Formula 保留一个字段，当获取所有警报时您将运行该字段（@Formula 将成为您已经在执行的查询的一部分，而不是新查询）

@Formula("(select count(1) from ALARM_IMAGE AI where AI.ALARM_FK = _this.ALARM_PK)") 
private Int alarmImageCount;

不太记得@Formula中引用的当前实体是什么，查看hibernate生成的sql就知道了，但我认为通常是_this

2。 看起来您正在使用primefaces，您可以执行诸如显示新页面之类的操作，但要保持图像计数丢失（或显示它们正在加载）直到它们完全加载，然后在它们被初始化时将它们ajax .这绝对可以完成，但需要一些时间。如果您要走这条路，请查看p:remoteCommand 组件和RequestContext 对象。