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

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"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd "> <!-- Generated 2015-4-10 11:00:59 by Hibernate Tools 4.0.0 --> <hibernate-mapping> <class name="com.xtest.models.EntityLayout" table="EntityLayout"> <id name="elSid" type="string"> <column name="el_sid" length="36"/> <generator class="org.hibernate.id.UUIDGenerator" /> </id> <many-to-one name="entityTables" class="com.xtest.models.EntityTables" fetch="select"> <column name="el_et_sid" length="36" /> </many-to-one> <property name="elName" type="string"> <column name="el_name" not-null="true" /> </property> <property name="elGroupName" type="string"> <column name="el_group_name" /> </property> <property name="elType" type="int"> <column name="el_type" not-null="true" /> </property> <property name="elStatusSid" type="string"> <column name="el_status_sid" /> </property> <property name="elDesc" type="string"> <column name="el_desc" /> </property> <set fetch="select" inverse="true" lazy="true" name="entityComposites" order-by="ecSortNo" sort="unsorted" table="EntityComposite"> <key> <column length="36" name="ec_el_sid"/> </key> <one-to-many class="com.xtest.models.EntityComposite"/> </set> <set fetch="select" inverse="true" lazy="true" name="entityLists" order-by="eldSortNo" sort="unsorted" table="EntityList"> <key> <column length="36" name="eld_el_sid"/> </key> <one-to-many class="com.xtest.models.EntityList"/> </set> <set fetch="select" inverse="true" lazy="true" name="entityForms" order-by="efdSortNo" sort="unsorted" table="EntityForm"> <key> <column length="36" name="efd_el_sid"/> </key> <one-to-many class="com.xtest.models.EntityForm"/> </set> <set fetch="select" inverse="true" lazy="true" name="entityTreeviews" order-by="etvSort" sort="unsorted" table="EntityTreeview"> <key> <column length="36" name="etv_el_sid"/> </key> <one-to-many class="com.xtest.models.EntityTreeview"/> </set> <set fetch="select" inverse="true" lazy="true" name="entityTreeviewCMenus" order-by="etvmName" sort="unsorted" table="EntityTreeviewCMenus"> <key> <column length="36" name="etvm_el_sid"/> </key> <one-to-many class="com.xtest.models.EntityTreeviewCMenus"/> </set> </class> </hibernate-mapping> 你看一下和这个有关系嘛
07-30
mybatis升级mybatisplus <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.1.6.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.cywlfw.www.yeswehave</groupId> <artifactId>YesWeHave</artifactId> <version>0.0.1-SNAPSHOT</version> <name>YesWeHave</name> <description>YesWeHave</description> <properties> <maven.build.timestamp.format>yyyy-MM-dd</maven.build.timestamp.format> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> <exclusions> <exclusion> <groupId>org.hibernate</groupId> <artifactId>hibernate-core</artifactId> </exclusion> <exclusion> <groupId>org.hibernate</groupId> <artifactId>hibernate-entitymanager</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jdbc</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-thymeleaf</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> <exclusions><!-- 去掉springboot默认配
03-11
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.3.12.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.goldwind.ipark</groupId> <artifactId>search-component-by-img-service</artifactId> <version>1.0.0</version> <name>search-component-by-img-service</name> <description>search-component-by-img-service</description> <properties> <java.version>1.8</java.version> <elasticsearch.version>7.17.3</elasticsearch.version> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <maven.compiler.source>1.8</maven.compiler.source> <maven.compiler.target>1.8</maven.compiler.target> <spring-boot-admin.version>2.4.3</spring-boot-admin.version> <spring-cloud.version>Hoxton.SR9</spring-cloud.version> <spring-cloud-alibaba-version>2.2.6.RELEASE</spring-cloud-alibaba-version> <skywalking.version>8.3.0</skywalking.version> <swagger.version>3.0.0</swagger.version> <poi.version>4.1.0</poi.version> <easypoi.version>4.1.2</easypoi.version> <maven.test.skip>true</maven.test.skip> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-mail</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency> <dependency> <groupId>org.springframework.session</groupId> <artifactId>spring-session-data-redis</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-configuration-processor</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>org.springframework.session</groupId> <artifactId>spring-session-core</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-devtools</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-openfeign</artifactId> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>cn.hutool</groupId> <artifactId>hutool-all</artifactId> <version>5.7.11</version> </dependency> <dependency> <groupId>io.springfox</groupId> <artifactId>springfox-swagger2</artifactId> <version>2.7.0</version> </dependency> <dependency> <groupId>io.springfox</groupId> <artifactId>springfox-swagger-ui</artifactId> <version>2.7.0</version> </dependency> <dependency> <groupId>org.apache.skywalking</groupId> <artifactId>apm-toolkit-logback-1.x</artifactId> <version>${skywalking.version}</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-pool2</artifactId> </dependency> <dependency> <groupId>com.xuxueli</groupId> <artifactId>xxl-job-core</artifactId> <version>2.1.2</version> </dependency> <dependency> <groupId>com.github.jsqlparser</groupId> <artifactId>jsqlparser</artifactId> <version>4.2</version> </dependency> <dependency> <groupId>com.github.pagehelper</groupId> <artifactId>pagehelper</artifactId> <version>5.2.1</version> <exclusions> <exclusion> <groupId>com.github.jsqlparser</groupId> <artifactId>jsqlparser</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.4.3.4</version> </dependency> <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-generator</artifactId> <version>3.5.1</version> </dependency> <dependency> <groupId>com.github.jeffreyning</groupId> <artifactId>mybatisplus-plus</artifactId> <version>1.5.1-RELEASE</version> </dependency> <dependency> <groupId>org.freemarker</groupId> <artifactId>freemarker</artifactId> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>druid-spring-boot-starter</artifactId> <version>1.2.6</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <scope>runtime</scope> </dependency> <dependency> <groupId>io.minio</groupId> <artifactId>minio</artifactId> <version>7.1.0</version> </dependency> <dependency> <groupId>org.springframework.kafka</groupId> <artifactId>spring-kafka</artifactId> </dependency> <dependency> <groupId>org.redisson</groupId> <artifactId>redisson-spring-data-23</artifactId> <version>3.17.1</version> </dependency> <dependency> <groupId>org.redisson</groupId> <artifactId>redisson-spring-boot-starter</artifactId> <version>3.17.1</version> <exclusions> <exclusion> <groupId>org.redisson</groupId> <artifactId>redisson-spring-data-26</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.elasticsearch.client</groupId> <artifactId>elasticsearch-rest-high-level-client</artifactId> </dependency> <dependency> <groupId>com.goldwind.ipark</groupId> <artifactId>iparkcommon</artifactId> <version>1.0.0-SNAPSHOT</version> </dependency> <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpcore</artifactId> </dependency> <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpmime</artifactId> </dependency> <dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> </dependency> <dependency> <groupId>com.google.code.gson</groupId> <artifactId>gson</artifactId> </dependency> <dependency> <groupId>net.sf.json-lib</groupId> <artifactId>json-lib</artifactId> <version>2.2.2</version> <classifier>jdk15</classifier> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.78</version> </dependency> <dependency> <groupId>io.jsonwebtoken</groupId> <artifactId>jjwt</artifactId> <version>0.9.0</version> </dependency> <dependency> <groupId>org.jfree</groupId> <artifactId>jfreechart</artifactId> <version>1.5.0</version> </dependency> <dependency> <groupId>commons-net</groupId> <artifactId>commons-net</artifactId> <version>3.8.0</version> </dependency> <dependency> <groupId>commons-io</groupId> <artifactId>commons-io</artifactId> <version>1.3.2</version> </dependency> <dependency> <groupId>org.jodd</groupId> 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<dependency> <groupId>org.apache.poi</groupId> <artifactId>poi-ooxml-schemas</artifactId> <version>${poi.version}</version> </dependency> <dependency> <groupId>org.hibernate.validator</groupId> <artifactId>hibernate-validator</artifactId> <version>6.2.0.Final</version> </dependency> <dependency> <groupId>cn.afterturn</groupId> <artifactId>easypoi-base</artifactId> <version>${easypoi.version}</version> </dependency> <dependency> <groupId>cn.afterturn</groupId> <artifactId>easypoi-web</artifactId> <version>${easypoi.version}</version> </dependency> <dependency> <groupId>cn.afterturn</groupId> <artifactId>easypoi-annotation</artifactId> <version>${easypoi.version}</version> </dependency> <dependency> <groupId>com.alibaba</groupId> <artifactId>easyexcel</artifactId> <version>3.0.5</version> </dependency> <dependency> <groupId>net.lingala.zip4j</groupId> <artifactId>zip4j</artifactId> <version>2.11.5</version> <!-- 检查最新版本 --> </dependency> <dependency> <groupId>io.milvus</groupId> 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springboot 工程的 pom.xml 的完整内容,现在启动工程报错 Caused by: java.lang.ClassNotFoundException: com.google.protobuf.MapFieldReflectionAccessor,帮我分析原因,告诉我如何修改?
06-13
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