Hibernate 的<generator class="native"></generator>的不同属性含义

本文介绍了Hibernate框架中多种主键生成策略,包括assigned、hilo、seqhilo、increment、identity、sequence、native、uuid.hex、uuid.string、foreign等,并探讨了它们的工作原理及适用场景。

http://blog.sina.com.cn/s/blog_7b8a637f010142if.html

1)assigned
主键由外部程序负责生成,无需Hibernate参与。

2)hilo
通过hi/lo 算法实现的主键生成机制,需要额外的数据库表保存主键生成历史状态。

3)seqhilo
与hilo 类似,通过hi/lo 算法实现的主键生成机制,只是主键历史状态保存在Sequence中,适用于支持Sequence的数据库,如Oracle。

4)increment
主键按数值顺序递增。此方式的实现机制为在当前应用实例中维持一个变量,以保存着当前的最大值,之后每次需要生成主键的时候将此值加1作为主键。
这种方式可能产生的问题是:如果当前有多个实例访问同一个数据库,那么由于各个实例各自维护主键状态,不同实例可能生成同样的主键,从而造成主键重复异常。因此,如果同一数据库有多个实例访问,此方式必须避免使用。

5)identity
采用数据库提供的主键生成机制。如DB2、SQL Server、MySQL中的主键生成机制。

6)sequence
采用数据库提供的sequence 机制生成主键。如Oralce 中的Sequence。

7)native
由Hibernate根据底层数据库自行判断采用identity、hilo、sequence其中一种作为主键生成方式。

8)uuid.hex
由Hibernate基于128 位唯一值产生算法生成16 进制数值(编码后以长度32 的字符串表示)作为主键。

9)uuid.string
与uuid.hex 类似,只是生成的主键未进行编码(长度16)。在某些数据库中可能出现问题(如PostgreSQL)。

10)foreign
使用外部表的字段作为主键。
一般而言,利用uuid.hex方式生成主键将提供最好的性能和数据库平台适应性。

另外由于常用的数据库,如Oracle、DB2、SQLServer、MySql 等,都提供了易用的主键生成机制(Auto-Increase 字段或者Sequence)。我们可以在数据库提供的主键生成机制上,采用generator-class=native的主键生成方式。
不过值得注意的是,一些数据库提供的主键生成机制在效率上未必最佳,大量并发insert数据时可能会引起表之间的互锁。数据库提供的主键生成机制,往往是通过在一个内部表中保存当前主键状态(如对于自增型主键而言,此内部表中就维护着当前的最大值和递增量),之后每次插入数据会读取这个最大值,然后加上递增量作为新记录的主键,之后再把这个新的最大值更新回内部表中,这样,一次Insert操作可能导致数据
库内部多次表读写操作,同时伴随的还有数据的加锁解锁操作,这对性能产生了较大影响。
因此,对于并发Insert要求较高的系统,推荐采用uuid.hex 作为主键生成机制

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 2.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"> <hibernate-mapping package="com.smics.apps.etst.domain.admin"> <class name="GroupFields"> <id name="id"> <generator class="native"/> </id> <property name="fieldsName" length='255'/> <property name="employeeNo" length='60'/> <property name="createDate" /> <property name="createdBy" length='60'/> </class> <class name="ReasonCode"> <id name="id"> <generator class="native"/> </id> <property name="codeType" length='20'/> <property name="smicTermCode" length='255'/> <property name="custCode" length='60'/> <property name="custTermCode" length='255'/> <property name="description" length='500'/> <property name="createDate" /> <property name="createdBy" length='60'/> </class> <class name="ResponserDept"> <id name="id"> <generator class="native"/> </id> <property name="orgId" length='255'/> <property name="deptName" length='255'/> <property name="secName" length='255'/> <property name="magrId" length='10'/> <property name="costCode" length='20'/> <property name="pieVerify" length='20'/> <property name="pieSite" length='20'/> <property name="createDate" /> <property name="createdBy" length='60'/> </class> <query name="findGroupByMember"><![CDATA[ from GroupFields g where g.employeeNo = ? ]]></query> <query name="findCccByMagrId"><![CDATA[ from ResponserDept g where g.magrId = ? ]]></query> <query name="findResponserDeptByOrgId"><![CDATA[ from ResponserDept g where g.orgId = ? ]]></query> <query name="findResDeptByDeptSec"><![CDATA[ from ResponserDept g where g.deptName = ? and g.secName = ? ]]></query> <query name="findResSecByDept"><![CDATA[ from ResponserDept g where g.deptName = ? ]]></query> <query name="findReasonCodeByCodeType"><![CDATA[ from ReasonCode r where r.codeType = ? ]]></query> </hibernate-mapping>
最新发布
08-29
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<alipay-sdk.version>4.34.0.ALL</alipay-sdk.version> <volc-sdk.version>LATEST</volc-sdk.version> </properties> <!-- 依赖管理(控制Spring Cloud Alibaba及相关组件版本) --> <dependencyManagement> <dependencies> <!-- Spring Cloud Alibaba 核心依赖管理 --> <dependency> <groupId>com.alibaba.cloud</groupId> <artifactId>spring-cloud-alibaba-dependencies</artifactId> <version>${spring-cloud-alibaba.version}</version> <type>pom</type> <scope>import</scope> </dependency> <!-- Spring Cloud 核心依赖管理 --> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>${spring-cloud.version}</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> <dependencies> <dependency> <groupId>jakarta.annotation</groupId> <artifactId>jakarta.annotation-api</artifactId> <version>2.1.1</version> </dependency> <!-- 一、Spring Boot 核心 Starter --> <dependency> <groupId>org.springframework.boot</groupId> 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<activation> <activeByDefault>true</activeByDefault> </activation> <properties> <spring-boot.run.profiles>dev</spring-boot.run.profiles> </properties> </profile> <profile> <id>prod</id> <properties> <spring-boot.run.profiles>prod</spring-boot.run.profiles> </properties> </profile> </profiles> </configuration> </plugin> <!-- 编译插件(指定Java版本) --> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.11.0</version> <configuration> <source>${java.version}</source> <target>${java.version}</target> <encoding>${encoding}</encoding> </configuration> </plugin> </plugins> <!-- 资源文件配置 --> <resources> <resource> <directory>src/main/resources</directory> <includes> <include>**/*.xml</include> <include>**/*.properties</include> <include>**/*.yml</include> <!-- 补充yml文件支持 --> </includes> <filtering>false</filtering> <!-- 不启用过滤 --> </resource> <!-- 多环境配置文件过滤 --> <resource> <directory>src/main/resources</directory> <includes> <include>application.properties</include> <include>application-${profiles.active}.properties</include> <include>application-${profiles.active}.yml</include> </includes> <filtering>true</filtering> <!-- 启用变量替换 --> </resource> </resources> </build> <!-- 多环境配置 --> <profiles> <profile> <id>dev</id> <properties> <profiles.active>dev</profiles.active> </properties> <activation> <activeByDefault>true</activeByDefault> </activation> </profile> <profile> <id>prod</id> <properties> <profiles.active>prod</profiles.active> </properties> </profile> </profiles> </project> 这是我的pom报错了 3.5.7 19:09:36.166 [main] WARN o.s.b.w.s.c.AnnotationConfigServletWebServerApplicationContext - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'securityConfig': Unsatisfied dependency expressed through field 'deviceAdminService': Error creating bean with name 'deviceAdminServiceImpl' defined in file [E:\core\main\target\classes\com\example\main\service\device\impl\DeviceAdminServiceImpl.class]: Post-processing of merged bean definition failed 19:09:36.183 [main] INFO o.a.catalina.core.StandardService - Stopping service [Tomcat] 19:09:36.204 [main] WARN o.a.c.loader.WebappClassLoaderBase - The web application [ROOT] appears to have started a thread named [Thread-2] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread: java.base@17.0.14/sun.net.dns.ResolverConfigurationImpl.notifyAddrChange0(Native Method) java.base@17.0.14/sun.net.dns.ResolverConfigurationImpl$AddressChangeListener.run(ResolverConfigurationImpl.java:176) 19:09:36.224 [main] INFO o.s.b.a.l.ConditionEvaluationReportLogger - Error starting ApplicationContext. To display the condition evaluation report re-run your application with 'debug' enabled. 19:09:36.246 [main] ERROR o.s.b.d.LoggingFailureAnalysisReporter - *************************** APPLICATION FAILED TO START *************************** Description: An attempt was made to call a method that does not exist. The attempt was made from the following location: org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$LegacyResourceElement.<init>(CommonAnnotationBeanPostProcessor.java:780) The following method did not exist: 'java.lang.String javax.annotation.Resource.lookup()' The calling method's class, org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$LegacyResourceElement, was loaded from the following location: jar:file:/E:/maven-repository/org/springframework/spring-context/6.1.10/spring-context-6.1.10.jar!/org/springframework/context/annotation/CommonAnnotationBeanPostProcessor$LegacyResourceElement.class The called method's class, javax.annotation.Resource, is available from the following locations: jar:file:/E:/maven-repository/org/apache/tomcat/annotations-api/6.0.53/annotations-api-6.0.53.jar!/javax/annotation/Resource.class jar:file:/E:/maven-repository/javax/annotation/javax.annotation-api/1.3.2/javax.annotation-api-1.3.2.jar!/javax/annotation/Resource.class The called method's class hierarchy was loaded from the following locations: javax.annotation.Resource: file:/E:/maven-repository/org/apache/tomcat/annotations-api/6.0.53/annotations-api-6.0.53.jar Action: Correct the classpath of your application so that it contains compatible versions of the classes org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$LegacyResourceElement and javax.annotation.Resource Disconnected from the target VM, address: '127.0.0.1:3673', transport: 'socket'
08-15
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