Question

我正在解决有关Hibernate延迟加载的问题。我在Hibernate论坛上发布了这个但没有得到答案，所以我想也许你们在stackoverflow上的人可能会帮我一臂之力。帖子链接是：https://forum.hibernate.org/viewtopic.php?f=1&t=1012419 我正在复制以下内容，提前感谢：

问题在于我正在尝试延迟加载一个集合，但它会一直急切加载，对我的应用程序性能产生巨大影响。这是场景，我描述了涉及的3个类的模型：

锦标赛：有一个联赛（锦标赛有默认联赛）。

联盟：有很多竞争对手 - 属于一个冠军（许多联赛属于一个锦标赛）。

当我加载锦标赛实体时，关联的联盟会带有已加载的竞争对手列表（即使我的映射文件中有lazy = true）。我正在粘贴这3个实体的映射文件的相关部分：

***************************************************************************************
<class name="Championship" table="Championships">

<id name="id" type="long" column="id">
  <generator class="native" />
</id>
<many-to-one name="defaultLeague" lazy="false" cascade="all" class="League" not-null="true"  column="Default_League_FK"  unique="true" not-found="ignore"/>

</class>

****************************************************************************************
<class name="League" table="League">

<id name="id" type="long" column="id">
  <generator class="native" />
</id>

<many-to-one name="championship" lazy="false"
class="Championship" column="Championship_FK" />

<list name="competitorsList" table="Competitors_League" cascade="all" lazy="true">
    <key column="League_FK" not-null="true"/>
<index column="LeagueIndex" type="long"/>
<one-to-many class="Competitor" />
</list>

</class>
*****************************************************************************************
<class name="Competitor" table="Competitors_League" >

<key column="id"/>

<many-to-one name="league" lazy="false" class="League" not-null="true" insert="false" update="false" column="League_FK" />

</class>
******************************************************************************************

当我加载锦标赛实例时，锦标赛 - ＆gt;联赛 - ＆gt; competList已经加载了所有列表元素。这不应该发生，因为我的联盟映射上有lazy = true：

<list name=" competitorsList" table="Competitors_League" cascade="all" lazy="true">

我尝试了很多不同的方法，即使看起来我的映射设置正确，我也可以使用它。

你能帮帮我吗？任何帮助都会非常感激，因为我有点被困在这里。

如果您需要任何额外信息，请与我们联系。谢谢！

评论说明

注1：在视图层中访问该集合（没有打开会话视图中的过滤器或类似的东西）。我应该收到“LazyInitializationException”，这是预期的行为，而是急切地加载集合。

注2：我正在添加类模型以提供一些额外的语义上下文：

public class League{

   private Championship championship;
       private List<Competitor> competitorsList;

}

*********************************

public class Championship {

   private League defaultLeague;
}
**********************************

public class Competitor{

   private League league;
}

注3：Hibernate.isInitialized（league.competitorList）返回TRUE。删除提取属性但行为相同。

注4：日志记录未显示已提取集合。我已经设置了DEBUG级别（无法使INFO级别抛出结果），这里是控制台输出。

19:14:35,953 DEBUG ErrorCounter:68 - throwQueryException() : no errors
19:14:35,959 DEBUG HqlSqlBaseWalker:111 - select << begin [level=1, statement=select]
19:14:35,966 DEBUG FromElement:108 - FromClause{level=1} :  com.sportsdt.model.championship (no alias) -> championship0_
19:14:35,972 DEBUG FromReferenceNode:51 - Resolved :  {synthetic-alias} -> {synthetic-alias}
19:14:35,979 DEBUG DotNode:569 - getDataType() : enJuego -> org.hibernate.type.BooleanType@1d50d84
19:14:35,985 DEBUG FromReferenceNode:51 - Resolved :  {synthetic-alias}.enJuego -> championship0_.en_juego
19:14:35,991 DEBUG FromReferenceNode:51 - Resolved :  {synthetic-alias} -> {synthetic-alias}
19:14:35,998 DEBUG DotNode:569 - getDataType() : competencia -> org.hibernate.type.ManyToOneType(com.sportsdt.model.Competencia)
19:14:36,004 DEBUG DotNode:526 - dereferenceShortcut() : property competencia in com.sportsdt.model.championship does not require a join.
19:14:36,011 DEBUG DotNode:555 - terminal propertyPath = [competencia]
19:14:36,017 DEBUG FromReferenceNode:51 - Resolved :  {synthetic-alias}.competencia -> championship0_.idCompetencia
19:14:36,023 DEBUG HqlSqlBaseWalker:117 - select : finishing up [level=1, statement=select]
19:14:36,030 DEBUG HqlSqlWalker:509 - processQuery() :  ( SELECT ( FromClause{level=1} championships championship0_ ) ( where ( and ( = ( championship0_.en_juego {synthetic-alias} enJuego ) ? ) ( = ( championship0_.idCompetencia {synthetic-alias} competencia ) ? ) ) ) )
19:14:36,036 DEBUG HqlSqlWalker:716 - Derived SELECT clause created.
19:14:36,042 DEBUG JoinProcessor:148 - Using FROM fragment [championships championship0_]
19:14:36,053 DEBUG HqlSqlBaseWalker:123 - select >> end [level=1, statement=select]
19:14:36,067 DEBUG AST:232 - --- SQL AST ---
-[SELECT] QueryNode: 'SELECT'  querySpaces (championships)
+-[SELECT_CLAUSE] SelectClause: '{derived select clause}'
|  +-[SELECT_EXPR] SelectExpressionImpl: 'championship0_.id as id29_' {FromElement{explicit,not a collection join,not a fetch join,fetch non-lazy properties,classAlias=null,role=null,tableName=championships,tableAlias=championship0_,origin=null,colums={,className=com.sportsdt.model.championship}}}
|  \-[SQL_TOKEN] SqlFragment: 'championship0_.nombre as nombre29_, championship0_.cantidadFechas as cantidad3_29_, championship0_.fecha_inicio as fecha4_29_, championship0_.fecha_fin as fecha5_29_, championship0_.en_juego as en6_29_, championship0_.idCompetencia as idCompet7_29_, championship0_.disponible_penca as disponible8_29_, championship0_.disponible_entrenador as disponible9_29_, championship0_.League_General_FK as League10_29_'
+-[FROM] FromClause: 'from' FromClause{level=1, fromElementCounter=1, fromElements=1, fromElementByClassAlias=[], fromElementByTableAlias=[championship0_], fromElementsByPath=[], collectionJoinFromElementsByPath=[], impliedElements=[]}
|  \-[FROM_FRAGMENT] FromElement: 'championships championship0_' FromElement{explicit,not a collection join,not a fetch join,fetch non-lazy properties,classAlias=null,role=null,tableName=championships,tableAlias=championship0_,origin=null,colums={,className=com.sportsdt.model.championship}}
\-[WHERE] SqlNode: 'where'
   \-[AND] SqlNode: 'and'
      +-[EQ] BinaryLogicOperatorNode: '='
      |  +-[DOT] DotNode: 'championship0_.en_juego' {propertyName=enJuego,dereferenceType=4,propertyPath=enJuego,path={synthetic-alias}.enJuego,tableAlias=championship0_,className=com.sportsdt.model.championship,classAlias=null}
      |  |  +-[IDENT] IdentNode: '{synthetic-alias}' {originalText={synthetic-alias}}
      |  |  \-[IDENT] IdentNode: 'enJuego' {originalText=enJuego}
      |  \-[PARAM] ParameterNode: '?' {ordinal=0, expectedType=org.hibernate.type.BooleanType@1d50d84}
      \-[EQ] BinaryLogicOperatorNode: '='
         +-[DOT] DotNode: 'championship0_.idCompetencia' {propertyName=competencia,dereferenceType=ROOT_LEVEL,propertyPath=competencia,path={synthetic-alias}.competencia,tableAlias=championship0_,className=com.sportsdt.model.championship,classAlias=null}
         |  +-[IDENT] IdentNode: '{synthetic-alias}' {originalText={synthetic-alias}}
         |  \-[IDENT] IdentNode: 'competencia' {originalText=competencia}
         \-[PARAM] ParameterNode: '?' {ordinal=1, expectedType=org.hibernate.type.ManyToOneType(com.sportsdt.model.Competencia)}

19:14:36,074 DEBUG ErrorCounter:68 - throwQueryException() : no errors
19:14:36,080 DEBUG QueryTranslatorImpl:216 - HQL: from com.sportsdt.model.championship where enJuego=? and competencia=?
19:14:36,086 DEBUG QueryTranslatorImpl:217 - SQL: select championship0_.id as id29_, championship0_.nombre as nombre29_, championship0_.cantidadFechas as cantidad3_29_, championship0_.fecha_inicio as fecha4_29_, championship0_.fecha_fin as fecha5_29_, championship0_.en_juego as en6_29_, championship0_.idCompetencia as idCompet7_29_, championship0_.disponible_penca as disponible8_29_, championship0_.disponible_entrenador as disponible9_29_, championship0_.League_General_FK as League10_29_ from championships championship0_ where championship0_.en_juego=? and championship0_.idCompetencia=?
19:14:36,092 DEBUG ErrorCounter:68 - throwQueryException() : no errors
19:14:54,360 DEBUG JDBCTransaction:103 - commit
19:14:57,136 DEBUG JDBCTransaction:193 - re-enabling autocommit
19:14:57,141 DEBUG JDBCTransaction:116 - committed JDBC Connection

如果我设置log4j.logger.org.hibernate.SQL = debug它会显示大量的select（正如预期的那样），这些操作包括对表的select和join，但是对于我看到的这个scrambled信息是没用的。

Answer 1

从未使用过基于xml的实体说明，但下面的链接可能对您有用。

http://java.sun.com/javaee/6/docs/api/javax/persistence/FetchType.html

定义从数据库中获取数据的策略。 EAGER 策略是持久性提供程序运行时的要求必须急切地获取数据。 LAZY战略暗示 持久性提供程序运行时，应该在延迟时获取数据它是第一次访问。 允许实施急切地获取 已指定LAZY策略提示的数据。

另一个问题是你如何确定竞争对手的急切负荷。例如，对getCompetitorsList().size()的任何调用都将导致加载列表。如果不是这种情况，你应该寻找可以保证延迟加载的特定于hibernate的配置选项。

Answer 2

您正在使用一对一关联。别。您的使用意味着联盟和冠军拥有相同的主键。

多对一的正确反转是“设置”

我无法从你的描述中告诉你。但是如果一个联盟在联盟中拥有一个冠军，你应该拥有：

    <set name="allChampions" access="field"
        cascade="all-delete-orphan" lazy="true">
        <key column="league" not-null="true"/>
        <one-to-many class="Championship"/>
    </set>

同样，除非您有理由订购竞争对手，否则您的竞争对手“名单”可能应该是一套。

顺便说一下，班级名称开头的所有空格都是什么？

更新

你怎么知道列表正在急切地被提取？我建议打开sql日志记录，以确保调试不会导致问题。
删除提取属性。 fetch会影响加载并对加载产生副作用。

使用org.hibernate.Hibernate.isInitialized（league.competitorList）查明列表是否真正初始化。

此log4j.xml代码段将有助于记录以确定何时获取集合：

   <logger name="org.hibernate">
      <level value="INFO"/>
   </logger>
    <!-- log HQL query parser activity -->
   <logger name="org.hibernate.hql.ast.AST">
      <level value="INFO"/>
   </logger>
    <!-- log just the SQL -->
   <logger name="org.hibernate.SQL">
      <level value="INFO"/>
   </logger>
    <!-- log JDBC bind parameters     -->
   <logger name="org.hibernate.type">
      <level value="INFO"/>
   </logger>

    <!-- log schema export/update -->
   <logger name="org.hibernate.tool.hbm2ddl">
      <level value="INFO"/>
   </logger>

    <!-- log HQL parse trees -->
   <logger name="org.hibernate.hql">
      <level value="INFO"/>
   </logger>
    <!-- log cache activity -->
   <logger name="org.hibernate.cache">
      <level value="INFO"/>
   </logger>
    <!-- log transaction activity (TRACE for very detailed) -->
   <logger name="org.hibernate.transaction">
      <level value="INFO"/>
   </logger>
   <!-- log JDBC resource acquisition -->
   <logger name="org.hibernate.jdbc">
      <level value="INFO"/>
   </logger>

正在急切地加载集合，即使lazy = true？

2 个答案: