Mybatis详细教程 （万字详解)

Mybatis 3.5.14

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01.简介

image-20240921222309384

1.1 官网

官方中文网: MyBatis中文网

  • 中文网参考手册

image-20240921222746402

1.2 概念

MyBatis 是一款优秀的持久层框架，支持自定义 SQL, 存储过程, 高级映射

  • 官方解释

image-20240921223207882

必要前置技术
  • Mysql [本课件以 MySQL 为例]
  • JDBC [Java Database Connection] API
通俗解释

  • Mybatis 框架 是对原生 JDBC 技术的封装 和 增强

  • Mybatis 框架 核心行为是将 JDBC ResultSet 结果集映射到类的过程 如

  • 映射关系示意

image-20240921223545754

02.入门

入门示例会引导大家熟悉 MYBATIS 环境 | 配置 | DAO 接口抽象配置 | 运行流程

2.1环境

Mybatis 当前最新版为 3.5.14 [此处创建项目 maven::java mybatis]

  • mybatis
<dependencies><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.14</version></dependency>
</dependencies>
  • pom.xml [mybatis-3.5.14.jar\META-INF\maven\org.mybatis\mybatis\pom.xml ]
<dependency><groupId>ognl</groupId><artifactId>ognl</artifactId><version>3.3.4</version><scope>compile</scope><optional>true</optional>
</dependency><dependency><groupId>org.javassist</groupId><artifactId>javassist</artifactId><version>3.29.2-GA</version><scope>compile</scope><optional>true</optional>
</dependency><dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.3.0</version>
<optional>true</optional>
</dependency><!--日志系列-->
<dependency><groupId>org.slf4j</groupId><artifactId>slf4j-api</artifactId><version>2.0.9</version><optional>true</optional>
</dependency><dependency><groupId>ch.qos.reload4j</groupId><artifactId>reload4j</artifactId><version>1.2.25</version><optional>true</optional>
</dependency><dependency><groupId>org.apache.logging.Log4j</groupId><artifactId>log4j-api</artifactId><version>${log4j.version}</version><optional>true</optional>
</dependency><dependency><groupId>commons-logging</groupId><artifactId>commons-logging</artifactId><version>1.2</version><optional>true</optional>
</dependency>
  • maven repository

image-20240922000431699

  • mysql
<!-- SQL: SELECT VERSION(): 查看自己的数据库版本--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version>
</dependency>
  • pom.xml [src/main/java 非java文件编译打包配置]
<build><resources><resource><directory>src/main/java</directory><includes><include>**/*.*</include></includes></resource><resource><directory>src/main/resources</directory><includes><include>**/*.*</include></includes></resource></resources>
</build>
  • pom.xml [完整]
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>test</groupId>  <!-- 此处可更改 可见我博客主页写的Maven博客--><artifactId>untitled</artifactId> <!-- 此处可更改 --><version>1.0-SNAPSHOT</version><properties><maven.compiler.source>17</maven.compiler.source><maven.compiler.target>17</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.14</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version></dependency><dependency><groupId>ognl</groupId><artifactId>ognl</artifactId><version>3.3.4</version><scope>compile</scope><optional>true</optional></dependency><dependency><groupId>org.javassist</groupId><artifactId>javassist</artifactId><version>3.29.2-GA</version><scope>compile</scope><optional>true</optional></dependency><dependency><groupId>cglib</groupId><artifactId>cglib</artifactId><version>3.3.0</version><optional>true</optional></dependency><!--日志 --><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-api</artifactId><version>2.0.9</version><optional>true</optional></dependency><dependency><groupId>ch.qos.reload4j</groupId><artifactId>reload4j</artifactId><version>true</version><optional>true</optional></dependency><dependency><groupId>org.apache.logging.log4j</groupId><artifactId>log4j-api</artifactId><version>${log4j.version}</version><optional>true</optional></dependency><dependency><dependency>commons-logging</dependency><artifactId>commons-logging</artifactId><version>1.2</version><optioanl>true</optioanl></dependency></dependencies><build><resources><resource><directory>src/main/java</directory><includes><include>**/*.*</include></includes></resource><resource><directory>src/main/resources</directory><includes><include>**/*.*</include></includes></resource></resources></build></project>

2.2 数据库

  • SQL
CREATE DATABASE mybatis;USE mybatus;CREATE TABLE user(user_id 			INT PRIMARY KEY AUTO_INCREMENT,user_username       VARCHAR(20)
)

2.3 实体类

package org.example.mybatis.entity;import lombok.Data;@Data
public class User {private Integer id;private String username;
}
// 写法二
// public record User(Integer id, String username) {
//
// }

2.4 核心配置文件

  • mybatis-config.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC"-//mybatis.org//DTD Config 3.0//EN""https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><environments default="dev"><environment id="dev"><transactionManager type="POOLED"/><dataSource type="JDBC"><property name="driver" value="com.mysql.cj.jdbc.Driver"/><!-- <property name="url" value="jdbc:mysql://127.0.0.1:3306(默认时可以省略掉)/mybatis?serverTimezone=Asia/Shanghai"/>--><property name="url" value="jdbc:mysql:///mybatis?serverTimezone=Asia/Shanghai"/><property name="username" value="root"/><property name="password" value="123456"/></dataSource></environment></environments></configuration>

2.5 Mapper 抽象

Mapper 接口是 DAO (Data Access Object) 操作，对数据库表的操作抽象

  • UserMapper.java
package org.exmaple.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.exmaple.mybatis.entity.User;@Mapper
public interface UserMapper {User selectById(int id);int deleteById(int id); // mysql返回值为一个状态值 可以使用 boolean 类型
}

2.6 Mapper 配置

Mapper 接口需通过配置 [Java | Xml] 方式告知 Mybatis 执行逻辑行为

  • org.example.mybatis.mapper.UserMapper.xml

    <?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><select id="selectById"parameterType="int"resultType="org.example.mybatis.entity.User">SELECTuser_id id,user_username usernameFORMuserWHEREuser_id = #{id}</select><delete id="deleteById" parameterType="int"> <!-- 无resultType参数可选 -->DELETE FROM user from user_id = #{id}</delete></mapper>

2.7 Mapper扫描

完成 Mapper 接口及其配置后 还需告知 Mybatis Mapper 接口位置

  • src/main/resources/mybatis-config.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC"-//mybatis.org//DTD Config 3.0//EN""https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><environments default="dev"><environment id="dev"><transactionManager type="POOLED"/><dataSource type="JDBC"><property name="driver" value="com.mysql.cj.jdbc.Driver"/><property name="url" value="jdbc:mysql:///Mybatis?serverTimezone=Asia/Shanghai"/><property name="username" value="root"/><property name="password" value="123456"/></dataSource></environment></environments><mappers><package name="org.example.mybatis.mapper"></package></mappers></configuration>

2.8 API 入口

Mybatis 提供运行的 入口 Api, 通过 Api 引导框架读取配置， 解析 Mapper 后才能正确运行

  • Application.java
package org.example.mybatis.api;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.example.mybatis.mapper.UserMapper;
import org.example.mybatis.entity.User;
import java.io.IOException;
import java.io.InputStream;public class Application {public static void main(String[] args) throws IOException {String resource = "mybatis-config.xml";InputStream config = Resources.getResourceAsStream(resource);SqlSessionFactory sqlSessionFactory =new SqlSessionFactoryBuilder().build(config);SqlSession sqlSession = sqlSessionFactory.openSession(true);UserMapper mapper = sqlSession.getMapper(UserMapper.class);User user = mapper.selectById(1);System.out.println(user);int row = mapper.deleteById(1);System.out.println("row=" + row);//  sqlSession.commit(); 开启autoCommit 或者手动提交sqlSession.close();}
}

2.9 日志

Mybatis 通过使用内置日志工厂提供日志工能

  • 官网日志机制

在这里插入图片描述

01.说明

  • 内置日志工厂将会把日志工作委托给下面的实现之一

  • SLF4J [日志抽象]

  • Apache Commons Logging [日志抽象]

  • Log4j 2 [日志实现]

  • Log4j (3.5.9起废弃)

  • JDK logging [日志实现 JDK自带 较少用]

  • 机制

	1. MyBatis 内置日志工厂基于运行时自省机制选择合适的日志工具2. MyBatis 会使用第一个查找得到的工具 (按上文列举的顺序查找) 如果一个都未找到，日志功能就会被禁用。
  • mybatis-config.xml [指定配置]
<configuration><serrings>...<setting name="logImpl" value="LOG4J"/> <!--可参考上文，上文已经配置完毕 -->...</serrings>
</configuration>
  • logImpl 可选的值有:
  • SLF4J, LOG4J, LOG4J2, JDK_LOGGING, COMMONS_LOGGING, STDOUT_LOGGING, NO_LOGGING
02.SLF4J

SLF4J 是一款日志门面抽象框架，本身并未实现，需使用具体的日志框架

  1. log4j 是一款实现的日志框架，对 SLF4J 有桥接实现
  2. log4j2 是log4j 2.y.z 版本, 同样对 SLF4J 有桥接实现
  3. logback 是 直接针对 SLF$J 实现的日志框架

官网: SLF4J Manual

  • 官方参考手册

image-20240922120637791

版本注意事项: https://github.com/gos-ch/slf4j

  • Github

image-20240922121133434

03.Logback

Logback 针对 SLF4J 的日志实现 核心坐标 [logback-core | logback-classsic]

  • dependency

image-20240922121805967

  • pom.xml
<!-- https://mvnrepository.com/artifact/ch.qos.logback/logback-classic -->
<dependency><groupId>ch.qos.logback</groupId><artifactId>logback-classic</artifactId><version>1.4.14</version><scope>test</scope>
</dependency>
  • API
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;public class HelloWorld {public static void main(String[] args) {Logger logger = LoggerFactory.getLogger(HelloWorld.class);logger.info("Hello World");}
}
  • logback.xml [不配置该文件时的内置日志格式]
<?xml version="1.0" encoding="UTF-8" ?>
<configuration><appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender" ><encoder><pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36}.%M %L - %msg%n<!-- %d日期 yyyy-MM-dd 年月日，HH:mm::ss.SSS时，分，毫秒，微秒 %t线程 %-5 左对齐5个字符 level级别%logger{36}长度为36的日志记录 .%M方法 %L行 - %msg具体信息 %n换行--></pattern></encoder></appender>
</configuration>

2.10 运行逻辑流程

了解 Mybatis 大致运行流程可以更清晰在整体上，对其有良好的认识

01.动态代理

动态代理实现主要有 JDK[仅支持接口 类型] | CGLIB [支持类和接口的 类型]

  • 这里仅需知晓

    • 生成的代理对象确实属于代理的接口类型，以及代理对象调用接口方法会执行到特定机制中

  • Mybatis 利用 动态代理 主要完成 mapper 代理 和 SQL 解析处理

  • ProxyUsage.java

package org.example.mybatis.api;import org.example.mybatis.mapper.UserMapper;import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;public class JdkProxyUsage {public static void main(String[] args) {ClassLoader loader = UserMapper.class.getClassLoader();Class<?>[] classes = { UserMapper.class };InvocationHandler handler = new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {System.out.println("method.getName() = " + method.getName());System.out.println("args[0] = " + args[0]);System.out.println("...");return null;}};UserMapper userMapper = (UserMapper) Proxy.newProxyInstance(loader, classes, handler);userMapper.deleteById(1000);}
}
02.Javassist

Javassist是 Apache 提供的动态字节码技术, 可动态生成类及类中成员

  • Mybatis 利用 Javassist 主要完成 对象成员对应列 延迟装配功能

  • JavassistUsage.java

package org.example.mybatis.api;import javassist.*;public class JavassistUsage {public static void main(String[] args) throws Exception {ClassPool classPool = ClassPool.getDefault();CtClass ctClass = classPool.makeClass("x.y.z.People");CtField ctField = CtField.make("private boolean alive;", ctClass);ctClass.addField(ctField);String methodBody = "public void message() { System.out.println(\"动态生成的方法\"); }";CtMethod ctMethod = CtMethod.make(methodBody, ctClass);ctClass.addMethod(ctMethod);ctClass.writeFile();}
}
03.逻辑流程
  1. 读取并，解析核心配置文件 mybatis-config.xml
  2. 装配数据库连接以及配置事务管理
  3. 读取 mapper 接口及 xml 文件所在位置并完成其对应的逻辑关联
  4. mapper 代理对象调用 mapper 接口方法时 mybatis 利用动态代理找到对应的标签 [xpath]
  5. mybatis 找到对应标签 解析 SQL 表达式及动态代理完成参数的适配
  6. mybatis 使用 JDBC 执行 SQL 操作， 拿到 ResultSet
  7. 通过配置告知 mybatis 列和对象属性的对应关系，让 mybatis 完整封装

03.全局配置

了解掌握 Mybatis 全局配置的 是将 Mybatis 熟练运用和解决问题的关键

  • Mybatis 全局配置都位于 mybatis-config.xml 中， 也可同理基于 Java 配置

image-20240923093855766

3.1 属性

Mybatis 允许读取外部 properties 文件，并读取为上下文 通过 ${key} 获取值

  • src/main/resources/db.properties
mysql.driver=com.mysql.cj.jdbc.Driver
mysql.url=jdbc:mysql:///Mybatis?serverTimezone=Asia/Shanghai <!-- 博主的数据库名为Mybatis-->
mysql.username=root
mysql.password=123456
  • mybatis-config-xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC"-//mybatis.org//DTD Config 3.0//EN""https://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><properties resource="db.properties"><!-- <property name="" value=""/> --></properties><environments default="dev"><environment id="dev"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${mysql.driver}"/><property name="url" value="${mysql.url}"/><property name="username" value="${mysql.username}"/><property name="password" value="${mysql.password}"/></dataSource></environment></environments><mappers><package name="org.example.mybatis.mapper"/></mappers>
</configuration>

3.2 设置

Mybatis 预留全局 key 用于控制 Mybatis 整体运行行为

  • 当未配置内全局 key 时, Mybatis 将使用默认的内置初始值
  • 参考链接: 配置_MyBatis中文网

image-20240923102507889

  • mybatis-config.xml
<settings><setting name="cacheEnabled" value="true"/><setting name="lazyLoadingEnabled" value="true"/><setting name="aggressiveLazyLoading" value="true"/><setting name="multipleResultSetsEnabled" value="true"/><setting name="useColumnLabel" value="true"/><setting name="useGeneratedKeys" value="false"/><setting name="autoMappingBehavior" value="PARTIAL"/><setting name="autoMappingUnknownColumnBehavior" value="WARNING"/><setting name="defaultExecutorType" value="SIMPLE"/><setting name="defaultStatementTimeout" value="25"/><setting name="defaultFetchSize" value="100"/><setting name="safeRowBoundsEnabled" value="false"/><setting name="safeResultHandlerEnabled" value="true"/><setting name="mapUnderscoreToCamelCase" value="false"/><setting name="localCacheScope" value="SESSION"/><setting name="jdbcTypeForNull" value="OTHER"/><setting name="lazyLoadTriggerMethods" value="equals,clone,hashCode,toString"/><setting name="defaultScriptingLanguage" value="org.apache.ibatis.scripting.xmltags.XMLLanguageDriver"/><setting name="defaultEnumTypeHandler" value="org.apache.ibatis.type.EnumTypeHandler"/><setting name="callSettersOnNulls" value="false"/><setting name="returnInstanceForEmptyRow" value="false"/><setting name="logPrefix" value="exampleLogPrefix_"/><setting name="logImpl" value="SLF4J | LOG4J | LOG4J2 | JDK_LOGGING | COMMONS_LOGGING | ..."/><setting name="proxyFactory" value="CGLIB | JAVASSIST"/><setting name="vfsImpl" value="org.mybatis.example.YourselfVfsImpl"/><setting name="useActualParamName" value="true"/><setting name="configurationFactory" value="org.mybatis.example.ConfigurationFactory"/>
</settings>

3.3 类型别名

类型别名可为 Mapper 接口返回的 [自定义类型] 定义一个短名称别名以便使用

3.3.1 自定义类型
  • mybatis-config.xml 自定义指定类型别名名称
<typeAliases><typeAlias alias="Author" type="domain.blog.Author"/><typeAlias alias="Bolg" type="domain.blog.Blog" /><typeAlias alist="Comment" type="domain.blog.Comment" /><typeAlias alist="Post" type="domain.blog.Post" /><typeAlias alias="Section" type="domain.blog.Section" /><typeAlias alias="Tag" type="domain.blog.Tag" />
</typeAliases>
  • mybatis-config.xml 指定包统一定义别名，规则是类名首字母小写作为名称
<typeAliases><packaage name="org.example.project.entity"/>
</typeAliases>
  • Author.java (不太推荐 当注解逐渐变多的时候类的格式会逐渐混乱)
@Alias("author")
public class Author {...
}
3.3.2 内置类型别名

官方网址: 配置_MyBatis中文网

image-20240923111817308

3.4 类型处理器

Mybatis 内置类型处理器用于完成 列和 对象属性的数据类型的对应关系

  • 当内置的所有处理器都不能对应 列和属性的数据类型时， Mybatis 将抛出异常

  • 解决

    • 调整 列 或者 属性的数据类型 使用 Mybatis 能够处理 [推荐]
    • 自行实现类型处理器并注册到 Mybatis 框架中 [注册分为全局和局部]
    01.内置类型处理器

    参考链接: 配置_MyBatis中文网

  • 内置类型处理器

image-20240923112454379

  • 自定义数据类型

Mybatis 内置 BaseTypeHandler 抽象用于实现自定义数据类型对应处理

  • BaseTypeHandler<泛型> 泛型表示 Java 数据类型

  • @MappedJdbcTypes (value = 数据库类型)

  • ExampleTypeHandler.java

package org.example.mybatis.type;import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;public class ExampleTypeHandler extends BaseTypeHandler<String> {@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType) throws SQLException {ps.setString(i, parameter);}@Overridepublic String getNullableResult(ResultSet rs, String columnName) throws SQLException {return rs.getString(columnName);}@Overridepublic String getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return rs.getString(columnIndex);}@Overridepublic String getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return cs.getString(columnIndex);}
}
  • GenderTypeHandler.java
package org.example.mybatis.type;import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.MappedJdbcTypes;
import org.example.mybatis.entity.Gender;import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;@MappedJdbcTypes(JdbcType.INTEGER)
public class GenderTypeHandler extends BaseTypeHandler<Gender> {@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, Gender gender, JdbcType jdbcType) throws SQLException {int sex = gender == Gender.MAN ? 0 : 1;ps.setInt(i, sex);}@Overridepublic Gender getNullableResult(ResultSet rs, String columnName) throws SQLException {int sex = rs.getInt(columnName);return sex == 0 ? Gender.MAN : Gender.WOMAN;}@Overridepublic Gender getNullableResult(ResultSet rs, int columnIndex) throws SQLException {int sex = rs.getInt(columnIndex);return sex == 0 ? Gender.MAN : Gender.WOMAN;}// 没有相关的调用方法@Overridepublic Gender getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return null;}
}
  • 全局注册
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC"-//mybatis.org//DTD Config 3.0//EN""https://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><properties resource="db.properties"><!-- <property name="" value=""/> --></properties><settings><setting name="cacheEnabled" value="true"/></settings><typeAliases><!-- <typeAlias alias = "User" type="org.example.mybatis.entity.User" />--><package name="org.example.mybatis.entity"/></typeAliases><typeHandlers><typeHandler handler="org.example.mybatis.type.GenderTypeHandler"/></typeHandlers><environments default="dev"><environment id="dev"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="${mysql.driver}"/><property name="url" value="${mysql.url}"/><property name="username" value="${mysql.username}"/><property name="password" value="${mysql.password}"/></dataSource></environment></environments><mappers><package name="org.example.mybatis.mapper"/></mappers></configuration>

3.5 对象工厂(仅了解)

MyBatis 创建结果对象实例是 都会使用一个内置对象工厂实例来完成实例化工作

  • 内置的对象工厂需要做的仅仅是实例化目标类， 要么通过默认无参构造方法，要么是有参构造

  • 如果像覆盖对象工厂的默认行为 可以通过创建自己的对象工厂来实现

  • ExampleObjectFactory.java (不推荐改,因为没有需求需要覆盖对象工厂，而且对技术要求极高)

public class ExampleObjectFactory extends DefaultObjectFactory {@Overridepublic <T> T create(Class<T> type) {return super.create(type);}@Overridepublic <T> T create(Class<T> type, List<Class<?>> constructorArgTypes, List<Object> constructorArgs) {return super.create(type, constructorArgTypes, constructorArgs);}@Overridepublic void setProperties(Properties properties) {super.setProperties(properties);}@Overridepublic <T> boolean isCollection(Class<T> type) {return Collection.class.isAssignableFrom(type);}
}
  • mybatis-config.xml
<objectFactory type="org.mybatis.example.ExampleObjectFactory"><property name="someProperty" value="100" />
</objectFactory>

3.6 插件

MyBatis 允许你在映射语句执行过程中的某一点进行拦截调用

  • Executor (update query flushStatements commit rollback getTransaction close isClosed)

  • ParameterHandler (getParameterObject setParameters)

  • ResultSetHandler (handleResultSets handleOutputParameters)

  • StatementHandler (perpare parameterize batch update query)

  • ExamplePlugin.java

@Intercepts ({@Signature (tyep= Executor.class,method = "update",args = {MappedStatement.class, Object.class})}
)public class ExamplePlugin implements Interceptor {@Overridepublic Object intercept(Invocation invocation) throws Throwable {// implement pre processing if needObject returnObject = invocation.proceed();// implement post processing if needreturn returnObject;}private Properties properties = new Properties();@Overridepublic void setProperties(Properties properties) {this.properties = properties;}
}
  • mybatis-config.xml
<plugins><plugin interceptor="org.mybatis.example.ExamplePlugin"><property name="someProperty" value="100"/></plugin>
</plugins>

3.7 环境配置

MyBatis 可以配置成适应多种环境 如 开发，测试，生产环境 需不同的配置

01 机制
  • 记住：尽管可以配置多个环境，但每个 SqlSessionFactory 实例只能选择一种环境
  • 每个数据库对应的 SqlSessionFactory
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(reader, environment);SqlSessionGactory factory = new SqlSessionFactoryBuilder().build(reader, enviroment, properties);
  • mybatis-config.xml
<environments default="development"><enviroment id="development"><transactionManager type="JDBC"><property name="..." value="..."/></transactionManager><dataSource type="POOLED"><property name="driver" value="${driver}"/><property name="url" value="${url}" /><property name="username" value="${username}"/><property name="password" value="${password}" /></dataSource></enviroment>
</environments>
02 事务管理器

Mybatis 关闭 MySQL 的事务自动提交，并推荐在关闭连接时，不再处理连接的事务自动提交

  • mybatis-config.xml
<transactionManager type="JDBC"><property name="skipSetAutoCommitOnClose" value="true" />
</transactionManager>

当 Mybatis + Spring 一起使用时 Mybatis 推荐使用 Spring 事务

  • 无论采用什么技术, 事务都应当放在业务层处理，持久层任何一个接口都是 单条 SQL操作

  • Demo

record UserService(UserMapper userMapper) {// 此处登录public void transferAccounts(int userId, int otherId, int amount) {userMapper.updateAmountById(userId, -amount); // 这是一条 SQLuserMapper.updateAmountById(otherId, +amount); // 这是一条 SQWL}
}

3.8 数据库厂商标识

MyBatis 可根据不同数据库厂商执行 同一 mapper 接口的不同 SQL 语句

01 数据库名称
package org.example.mybatis.api;import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.SQLException;public class JdbcApi {public static void main(String[] args) throws SQLException {String url = "jdbc:mysql:///mybatis?serverTimezone=Asia/Shanghai";Connection connection = DriverManager.getConnection(url, "root", "123456");DatabaseMetaData metaData = connection.getMetaData();String productName = metaData.getDatabaseProductName();System.out.println("productName =" + productName);}}
02 标识机制
  • mybatis-config.xml
<databaseIdProvider type="DB_VENDOR"><property name="SQL Server" value="sqlserver" /><property name="DB2" value="db2" /><property name="Oracle" value="oracle" /><property name="数据库产品名称" value="别名" />
</databaseIdProvider>
  • mapper [针对 selectById 方法可提前配置多条 SQL语句]
<select id="selectById"parameterType="_int"resultType="user"databaseId="oracle">SELECTuser_id id,user_username usernameuser_create_datetime createDatetimeuser_gender genderFROMuserWHERE user_id = #{id}
</select><select id="selectById"parameterType="_int"resultType="user"databaseId="mysql">SELECTuser_id id,user_username usernameuser_create_datetime createDatetimeuser_gender genderFROMuserWHERE user_id = #{id} AND 1 = 1 <!--为了区别上一个select语句-->
</select>

[!note]

备注: 实际开发时因尽量使用 SQL规范关键值或查询方式， 避免使用数据库特殊关键值

3.9 映射器

映射器是 Mybatis 预言指定 Mapper 接口所在位置的手段

  • 其指定逻辑方式有：mybatis-config.xml 使用 mappers 标签配置

  • 指定 全限定名 mapper xml 位置 路径目录用 / 表示

  • 指定 全限定名 本地 mapper xml 本地位置

  • 指定 全限定名 mapper 接口 位置 路径目录用 .表示

  • 指定 全限定名 mapper 接口所在包位置 路径目录用 .表示[常用]

  • mappers

<!-- 使用相对于类路径的资源引用 -->
<mappers><mapper resource="org/mybatis/builder/AuthorMapper.xml"/><mapper resource="org/mybatis/builder/BlogMapper.xml"?><mapper resource="org/mybatis/builder/PostMapper.xml">
</mappers>
  • mappers
<!--使用完全限定资源定位符（URL）-->
<mappers>
<mapper urL="file:///var/mappers/AuthorMapper.xm"/>
<mapper url="file:///var/mappers/BlogMapper.xmL"/>
<mapper urL="file:///var/mappers/PostMapper.xmL"/>
</mappers>
  • mappers
<!--使用映射器接口实现类的完全限定类名 -->
<mappers>
<mapper class="org.mybatis.builder.AuthorMapper"/>
<mapper class="org.mybatis.builder.BlogMapper"/>
<mapper class="org.mybatis.builder.PostMapper"/>
</mappers>
  • mappers
<!-- 将包内的映射器接口全部注册为映射器 -->
<mappers><package name="org.mybatis.builder"/>
</mappers>

04.映射文件

Mapper.xml 中 mapper 根元素下只允许出现以下子元素

----- SQL 映射文件只有很少的几个顶级元素 (按照应被定义的顺序列出)

  • cache - 该命名空间的缓存配置

  • cache-ref -引用其他命名空间的缓存配置

  • resultMap -描述如何从数据库结果集中加载对象，是最复杂也是最强大的元素

  • sql - 可被其他语句引用的可重用语句块

  • insert - 映射插入语句

  • update -映射更新语句

  • delete -映射删除语句

  • select -映射查询语句

4.1 select

select 标签用于 SQL 查询和逻辑映射

01 属性列表
  • select 标签元素只允许的出现的属性
<selectid="methodName"parameterType="int"parameterMap="deprecated"resultType="hashmap"resultMap="resultMapId"flushCache="false"useCache="true"timeout="10"fetchSize="256"statementType="PREPARED"resultSetType="FORWARD_ONLY">
  • select 标签属性说明

image-20240924104447487

02 resultType

resultType 用于返回类型，基础类型，Map, 集合，对象类型

01 基础类型【单个值】
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.Gender;
import org.exampl.mybatis.entity.User;import java.util.List;
import java.util.Map;@Mapper
public interface UserMapper {User selectById(int id);User selectByUsernameAndGender(User user);User selectByGenderAndUsername(@Param("gender") Gender gender,@Param("username") String username);long count();String selectUsernameById(int id);}
02 对象类型
  • 略
03 集合对象类型
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.Gender;
import org.example.mybatis.entity.User;import java.util.List;
import java.util.Map;@Mapper
public interface UserMapper {User selectById(int id);User selectByUsernameAndGender(User user);User selectByGenderAndUsername(@Param("gender") Gender gender,@Param("username") String username);long count();String selectUsernameById(int id);List<User> selectList();
}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><select id="selectById" parameterType="_int" resultType="User">SELECTuser_id id,user_username username,user_create_datetime createDateTime,user_gender genderFROMuserWHERE user_id = #{id}</select><select id="selectByUsernameAndGender" parameterType="User" resultType="User">SELECTuser_id id,user_username username,user_create_datetime createDatetime,user_gender genderFROMuserWHEREuser_username = #{username} AND user_gender = #{gender}</select><select id="selectByGenderAndUsername" resultTyep="User">SELECT user_id id,user_username username,user_create_datetime createDatetime,user_gender genderFROMuserWHEREuser_username = #{username} AND user_gender = #{gender}</select><select id="count" resultType="_long">SELECT COUNT(1) FROM user</select><select id="selectUsernameById" parameterType="_int" resultType="string">SELECT user_username FROM user WHERE user_id = #{id}</select><select id="selectList" resultType="User">SELECT user_id id,user_username username,user_creae_datetime createDateTime,user_gender genderFROMuser</select>
</mapper>
04 Map类型
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.Gender;
import org.example.mybatis.entity.User;import java.util.List;
import java.util.Map;@Mapper
public interface UserMapper {User selectById(int id);User selectByUsernameAndGender(User user);User selectByGenderAndUsername(@Param("gender") Gender gender,@Param("username") String username);long count();String selectUsernameById(int id);List<User> selectList();Map<String Object> selectByIdToHashMap(int id);List<Map<String, Object>> selectListOfHashMap();}

4.2 insert update delete

insert update delete 用于完成 插入 更新 删除

01 属性列表
<insertid="insertAuthor"parameterType="domain.blog.Ahthor"flushCache="true"statementType="PREPARED"keyProperty=""useGeneratedKeys=""timeout="20">
</insert>
<updateid="updateAuthor"parameterType="domain.blog.Author"flushCache="true"statementType="PREPARED"timeout="20">
</update>
<deleteid="deleteAuthor"parameterType="domain.blog.Author"flushCache="true"statementType="PREPARED"timeout="20">
</delete>
  • 属性说明

image-20240924222443061

强调
  1. insert update delete 没有返回指定的类型
  2. insert update delete 只能返回 int 或 boolean 类型
增改删实例
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotation.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.Gender;
import org.example.mybatis.entity.User;import java.util.List;
import java.util.Map;@Mapper
public interface UserMapper {int insert(User user);int updateUsernameById(@Param("username") String username,@Param("id") int id);int deleteByLikeUsername(String username);}
  • UserMapper.xml
<?xml version="1.0" encoding="TUF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><insert id="insert" parameterType="User">INSERT INTO user(user_id,user_username,user_create_datetime,user_gender)VALUE (null,#{username},#{createDatetime},#{gender})</insert><update id="updateUsernameById">UPDATE user SET user_username = #{username} WHERE user_id = #{id}</update><delete id="deleteByLikeUsername" parameterType="string">DELETE FROM WHERE user_name LIKE CONCAT('%', #{username}, '%')</delete>
</mapper>
02 自增主键
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.Gender;
import org.example.mybatis.entity.User;import java.util.List;
import java.util.Map;@Mapper
public interface UserMapper {int insert(User user);}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><insert id="insert"patameterType="User"userGeneratedKeys="true"keyColumn="user_id"keyProperty="id">INSERT INTO user(user_id,user_username,user_create_datetime,user_gender)VALUES (null,#{username},#{createDatetime},#{gender})</insert></mapper>

4.3 参数

Mybatis 无论查询还是更新 都支持单个基本参数，对象参数，多个基本参数

  • parameterType 支持单个基本参数
  • parameterType 对象参数
  • parameterType 多个基本参数
01 单个参数
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis,entity.Gender;
import org.example.mybatis.entity.User;@Mapper
public interface UserMapper {public User selectById(int id);}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><select id="selectById" parameterType="_int" resultType="User">SELECTuser_id id,user_username username,user_create_datetime createDatetime,user_gender genderFROM	userWHEREuser_id = #{id}</select></mapper>
02 对象参数
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotaions.Param;
import org.example.mybatis.entity.Gender;
import org.example.mybatis.entity.User;@Mapper
public interface UserMapper {public User selectById(int id);public User selectByUsernameAndGender(User user);}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"<select id="selectById" parameterType="_int" resultType="User">SELECTuser_id id,user_username username,user_create_datetime createDatetime,user_gender genderFROMuserWHEREuser_id = #{id}</select>
03 多个参数
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.Gender;
import org.example.mybatis.entity.User;@Mapper
public interface UserMapper {public User selectById(int id);public User selectByUsernameAndGender(User user);public User selectByGenderAndUsername(@Param("gender") Gender gender),@Param("username") String username);
}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><select id="selectById" parameterType="_int" resultType="User">SELECTuser_id id,user_username usernameuser_create_datetime createDatetime,user_gender genderFROMuserWHEREuser_id = #{id}</select><select id="selectByUsernameAndGender" parameterType="User" resultType="User">SELECTuser_id id,user_username usernameuser_create_datetime createDatetime,user_gender genderFROMuserWHEREuser_username = #{username} AND user_gender = #{gender}</select><select id="selectByGenderAndUsername" resultType="User">SELECTuser_id id,user_username usernameuser_create_datetime createDatetime,user_gender genderFROMuserWHEREuser_username = #{username} AND user_gender = #{gender}</select>
</mapper>

4.4 高级结果映射

resultMap 可完成单个类型，嵌套类型等复杂类型指定映射

01 resultMap

  • resultMap 子标签

    • constructor 用于指定构造方法创建对象
      • idArg 指定 主键列 列提高性能
      • arg 指定 普通列

  • id 无参构造创建对象 指定 主键 列

  • result 无参构造创建对象 指定 普通列

  • association 指定嵌套结果集映射

  • collection 指定被集合包裹的嵌套结果集映射

  • discriminator 指定某列值来决定选取 另外的 ResultMap 映射

    • case

  • resultMap 属性

    • id 指定当前映射的 ID 唯一标识
    • type 指定当前映射的主类型
    • autoMapping 开启或关闭默认自动映射 会覆盖 autoMappingBehavior 默认 unset
02 基础使用

实体类

  • User.java
package org.example.mybatis.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import java.time.LocalDateTime;@Data
@AllArgsConstructor
@NoArgsConstructorpublic class User {private Integer id;private String username;private LocalDateTime createDatetime;private String gender;}

  • Mapper

  • UserMapper.java

package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.User;import java.util.List;@Mapper
public interface UserMapper {User selectById(int id);List<User> selectList();
}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org///DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><!-- <resultMap id="baseUser" type="User"><constructor><idArg column="user_id" javaType="integer"/><arg column="user_username" javaType="string"/><arg column="user_create_datetime" javaType="java.time.LocalDateTime"/><arg column="user_gender" javaType="string"/></constructor></resultMap>--><resultMap id="baseUser" type="User" autoMapping="false"><id column="user_id" property="id"/><result column="user_username" property="username"/><result column="user_create_datetime" property="createDatetime"/><result column="user_gender" property="gender"/></resultMap><select id="selectById" parameterType="_int" resultMap="baseUser">SELECTuser_id,user_username,user_create_datetime,user_genderFROMuserWHEREuser_id = #{id}</select><select id="selectList" resultMap="baseUser">SELECTuser_id,user_username,user_create_datetime,user_genderFROMuser</select>
</mapper>
03 association

association 用于完成嵌套结果集映射, 嵌套关系是 Java 的和 Mybatis 无关

  • association 允许指定指定列映射到 类中各个复杂成员

第一种 一条 SQL语句

  • Role.java
package org.example.mybatis.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
@NoArgsConstructor
@AllArgsConstructor
public class Role {private Integer id;private String name;}
  • User.java
package org.example.mybatis,entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok,NoArgsConstructor;import java.time.LocalDateTime;@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {private Integer id;private String username;private LocalDateTime createDatetime;private Role role;
}
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.User;import java.util.List;@Mapper
public interface UserMapper {User selectById(int id);List<User> selectList();
}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><resultMap id="baseUser" type="User" autoMapping="false"><id column="user_id" property="id"/><result column="user_username" property="username"/><result column="user_create_datetime" property="createDatetime"/><result column="user_gender" property="gender"/></resuLtMap><resultMap id="baseRole" type="Role"><id column="role_id" property="id"/><result column="role_name" property="name"/></resultMap><resultMap id="userAndRole" type="User" extends="baseUser"><association property="role" resultMap="baseRole" fetchType="lazy"/></resultMap><select id="selectById" parameterType="_int" resultMap="userAndRole">SELECTU.user_id,U.user_username,U.user_create_datetime,U.user_gender,R.role_id,R.role_nameFROMUserUJOINuser_role URON		U.user_id = #{id} AND U.user_id = UR.ur_user_idJOINRole RON		UR.ur_role_id = R.role_id</select><select id="selectList" resultMap="baseUser">SELECTuser_id,user_usernameuser_create_datetime,user_genderFROMuser</select></mapper>

第二种 多条SQL 语句 [各独立 Mapper]

  • RoleMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotationsMapper;
import org.example.mybatis.entity.Role;@Mapper
public interface RoleMapper {Role selectByUserId(int userId);
}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.RoleMapper"><resultMap id="baseRole" type="Role"><id column="role_id" property="id"/><result column="role_name" property="name"/></resultMap><select id="selectByUserId" parameterType="_int" resultMap="baseRole">SELECTR.role_id,R.role_nameFROMRole RJOINuser_role URONR.role_id = UR.ur_role_id AND UR.ur_user_id = #{userId}</select></mapper>
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><resultMap id="baseUser" type="User"autoMapping="false"><id column="user_id" property="id"/><result column="user_username" property="username"/><result column="user_create_datetime" property="createDatetime"/><result column="user_gender" property="gender"/></resuLtMap><resultMap id="userAndRole"type="User"extends="baseUser"><association property="role"select="org.example.mybatis.mapper.RoleMapper.selectByUserId"column="user_id"fetchType="lazy"/></resultMap><!-- 	<resultMap id="baseRole" type="Role"><id column="role_id" property="id"/><result column=”role_name" property="name"/></resultMap><resultMap id="userAndRole” type="User" extends="baseUser"><association property="role” resultMap="baseRole" fetchType="lazy"/></resultMap>--><select id="selectById" parameterType="_int" resultMap="userAndRole">SELECTuser_id,user_username,user_create_datetime,user_genderFROMuserWHEREuser_id =#{id}</select>
</mapper>
04 collection
  • DepartmentMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.RoleMapper"><resultMap id="baseDepartment" type="Department"><id column="department_id" property="id"/><result column="department_name" property="name"/></resultMap><resultMap id="baseEmployee" type="Employee"><id column="employee_id" property="id"/><result column="employee_name" property="name"?/><result column="employee_phone" property="phone"/></resultMap><resultMap id="deparmentAndEmployee" type="Department" extends="baseDepartment"><colleciont property="employees"javaType="list"ofType="Employee"resultMap="baseEmployee"fetchType="lazy"/></resultMap><select id="selectById" parameterType="_int" resultMap="departmentAndEmployee">SELECTD.department_id,D.department_name,E.employee_id,E.employee_name,E.employee_phoneFROMdepartment DJOIN 	employee EOND.department_id = #{id} AND D.department_id = E.employee_department_id</select>
</mapper>

自行 SQL 逻辑关联

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.RoleMapper"><resultMap id="baseEmployee" type="Employee"><id column="employee_id" property="id"/><result column="employee_name" property="name"/><result column="employee_phone" property="phone"/></resultMap><select id="selectByDepartmentId" parameterType="_int" resultMap="">SELECT employee_id,employee_name,employee_phone,FROMemployeeWHEREemployee_department_id = #{departmentId}</select>
</mapper>
05 discriminator

期望根据某个列的值 [这个指一般固定 比如 男 女] 再来决定指定那个 resultMap 映射

  • SQL
CREATE TABLE people (people_id INT PRIMARY KEY AUTO_INCREMENT,people_id VARCHAR(10),people_phone VARBINARY(12),people_gender VARCHAR(10)
)CREATE TABLE male_health_form (mhf_id INT PRIMARY KEY AUTO_INCREMENT,mhf_height INT,mhf_weight INT,mhf_pulmonary INT,mhf_strong INT,mhf_people_id INT
)CREATE TABLE female_health_foem (fhf_id       INT PRIMARY KEY AUTO_INCREMENT,fhf_height	 INT,fhf_weight   INT,fhf_bust	 INT,fhf_waist    INT,fhs_people_id   INT
)

实体类

  • People.java
package org.example.mybatis.entity;import lombok.Data;@public class People {private Integer id;private String name;private String phone;private String gender;private HealthForm healthForm;
}
  • HealthForm.java
package org.example.mybatis.entity;import lombok.Data;@Data 
public class HealthForm {private Integer id;private Integer height;private Integer weight;
}
  • MaleHealthForm.java
package org.example.mybatis.entity;import lom.bok.Data;@Data
public class MaleHealthForm extends HealthForm {private Integer pulmonary;private Integer strong;}
  • FemaleHealthForm.java
package org.example.mybatis.entity;import lombok.Data;@Data
public class FemaleHealthForm extends HealthForm {private Integer bust;private Integer waist;}
  • PeopleMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis,entity.People;@Mapper
public interface PeopleMapper {People selectById(int id);}
  • PeopleMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.PeopleMapper"><resultMap id="basePeople" tyle="People"><id column="people_id" property="id"/><result column="people_name" property="name"/><result column="people_phone" property="phone"/><result column="people_gender" property="gender"/></resultMap><resultMap id="maleForm" type="MaleHealthForm"><id column="mhf_id" property="id"/><result column="mhf_height" property="height"/><result column="mhf_weight" property="weight"/><result column="mhf_pulmonary" property="puLmonary"/><result column="mhf_strong" property="strong"/></resultMap><resultMap id="femaleForm" type="FemaleHealthForm"><id column="fhf_id" property="id"/><result column="fhf_height" property="height"/><result column="fhf_weight" property="weight"/><result column="fhf_bust" property="bust"/><result column="fhf_waist" property="waist"/></resultMap><resultMap id="peopleAndHealthForm" type="People" extends="basePeople"><association property="healthForm"><discriminator javaType="string" column="people_gender"><case value="MALE" resultMap="maleForm"/><case value="FEMALE" resuLtMap="femaLeForm"/></discriminator></association></resultMap><select id="selectById" parameterType="_int" resultMap="peopleAndHealthForm">SELECTP.people_id,P.people_name,P.people_phone,P.people_gender,MHF.mhf_id,MHF.mhf_height,MHF.mhf_weight,MHF.mhf_pulmonary,MHF.mhf_strong,FHF.fhf_id,FHF.fhf_height,FHF.fhf_weight,FHF.fhf_bust,FHF.fhf_waistFROM 	people PLEFT JOINmale_health_form MHFON		P.people_id = MHF.mhf_people_idLEFT JOINfemale_health_form FHFON		P.people_id = FHF.fhf_people_idWHERE	P.people_id= #{id}</select></mapper>
06 反向关联

Mybatis 的关联关系是单项的，如果有双向关联则是相互独立的

  • 若有双向关联时，要注意 A 关联 B 关联 A [此时这个 A 不能再关联 B了] 否则死循环

  • 解决方式为 灵活选择 ResultMap

  • 避免双向关联， 设计时考虑从主到次的关联方式

  • Employee.java

package org.example.mybatis.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
@AllArgsConstructor
@NoArgsConstructor
public class Employee {private Integer id;private String name;private String phone;private Department department;
}
  • EmployeeMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.EmployeeMapper"><resuLtMap id="baseEmployee" type="Employee"><id column="employee_id" property="id"/><result column="employee_name" property="name"/><result column="empLoyee_phone" property="phone"/></resultMap><resuLtMap id="empLoyeeAndDepartment"type="Employee"eextends="baseEmpLoyee"><association property="department"column="employee_department_id"select="org.example.mybatis.mapper.DepartmentMapper._selectById"fetchType="lazy"/></resultMap><select id="selectByDeartmentId"parameterType="_int"resuLtMap="empLoyeeAndDepartment">SELECTemployee_id,employee_name,employee_phone,employee_department_idFROMemployeeWHEREemployee_department_id = #{departmentId}</select>
</mapper>
  • DepartmentMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.EmployeeMapper"><resultMap id="baseDepartment" type="Department"><id column="department_id" property="id"/><result column="department_name" property="name"/></resultMap><resultMap id="departmentAndEmployee" type="Department" extends="baseDepartment"><collection property="employees"javaType="list"ofType="EmpLoyee"column="department_id"select="org.example.mybatis.mapper.EmployeeMapper.selectByDepartmentId"fetchType="lazy"/></resultMap><select id="selectById" parameterType="_int" resuLtMap="departmentAndEmployee">SELECTdepartment_id,department_nameFROMdepartmentWHEREdepartment_id =#(id}</select><select id="_selectById" parameterType="_int" resultMap="baseDepartment">SELECTdepartment_id,department_nameFROMdepartmentWHEREdepartment_id =#{id}</select></mapper>

4.5 自动映射

Mybatis 默认支持两种情况的自动映射

  1. 当表列名和对象属性名称一致时, mybatis 能完自动映射 [可借助此点给列别名]
  2. 开启全局驼峰映射时，列 user_id，属性 userId, mybatis 能完自动映射

4.6 缓存

Mybatis 有一级缓存默认开启，二级缓存需 cache 标签配置

01 一级缓存

Mybatis 的一级缓存是针对 SqlSession

  • 证据 [多次执行相同查询 不会多次发送 SQL 语句]
package org.example.mybatis.api;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatisl.session.SqlSessionFactoryBuilder;
import org.example.mybatis.mapper.UserMapper;import java.io.IOException;
import java.io.Reader;public class Application {String resources = "mybatis-config.xml";Reader config = Resources.getResourceAsReader(resources);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(config);UserMapper userMapper = sqlSession.getMapper(UserMapper.class);userMapper.selectById(1);userMapper.selectById(1);userMapper.selectById(1);sqlSession.close();.
}

  • 只要查询就会被缓存到 SqlSession， 只要查询就会刷新 SqlSession 缓存， 只要更新就会刷新当前对应 namespace SqlSession 缓存。

  • Mybatis 一级缓存是基于命名空间隔离的， 各个 namespace 不会互相影响

  • 一级缓存难以享受且暴力，没有良好的可视化管理方案

02 二级缓存

二级缓存基于 SqlSessionFactory 先获取一级缓存 若无 再获取二级缓存

证据
package org.example.mybatis.api;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlsessionFactory;
import org.apache.ibatis.session.SqlsessionFactoryBuilder;
import org.example.mybatis.mapper.UserMapper;import java.io.IOException;
import java.io.Reader;public class Application {public static void main(String[] args) throws IOEception {String resources = "mybaits-config.xml";Reader config = Resources.getResourceAsReader(resorces);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().builder(config);SqlSession sqlSessionl = sqlSessionFactory.openSession();UserMapper userMapper1 = sqlSession1.getMapper(UserMapper.class);userMapper1.selectById(1);sqlSession1.commit();SqlSession sqlSession2 = sqlSessionFactory.openSession();UserMapper userMapper2 = sqlSession2.getMapper(UserMapper.class);userMapper2.selectById(1);sqlSession2.commit();}
}
缓存命中率

image-20240927131212183

结论

  • 二级缓存默契开启，但需要使用 < cache> 标签显式对其使用 cache 可轻微控制缓存算法等

  • 二级缓存是基于命名空间隔离的， 各个 namespace 不会相互影响

  • 二级缓存在暴力， 没有良好的可视化管理方案

  • 二级缓存有命中率的概念

  • 特殊的

    • 无论一级二级缓存 数据库没有数据也是一种数据 null 也会缓存
03 缓存方案

  1. 缓存方案应该业务层中实现，业务层会处理数据， 业务层才对业务敏感

  2. 缓存方案必须放在读多写少的场景，否则缓存难以享受且徒增系统负担

  3. 缓存方案必须保证 查询被缓存，更新可能要清除缓存 [是否一定清除看策略]

  4. 缓存方案可以借助 命名空间 + KEY, 思路去隔离缓存来进行管理

  5. 缓存方案不一定非要等到更新操作去刷新缓存, 可以周期性的刷新

  6. 缓存要提供良好的可视化管理方案

4.7 sql

sql 标签用于组装重复的 SQL 语句，不推荐使用 会使得 Mapper 难以维护

  • UserMapper.java
pack org.example.mybaits.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.User;import java.util.List;@Mapper
public interface UserMapper {User selectById(int id);List<User> selectList();
}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.UserMapper"><sql id="baseSelectUser">SELECTuser_id id,user_username username,user_create_datetime createDateTime,user_gender genderFROMuser</sql><select id="selectById" parameterType="_int" resultType="User"><include refid="baseSelectUser"/>WHEREuser_id = #{id}</select><select id="selectList" resultType="User"><include refid="baseSelectUser"/></select></mapper>

05.动态SQL

Mybatis 提供一些特殊标签 用于运行时拼接 SQL语句

  • if | choose | when | otherwise | where |set | bind | foreach
  • 以上标签都是 select | update | delete 的子元素

5.1 where if

  • Mapper.xml
<select id="selectByCondition" parameterType="User" resultMap="baseUser">SELECTuser_id,user_username,user_create_datetime,user_genderFROMuser<where><if test="username != null">user_username = #{username}</if><if test="gender != null">AND user_gender = #{gender}                          </if></where>
</select>

5.2 choose, when, otherwise

  • Mapper.xml
<select id="selectByOnlyOneCondition" parameterType="User" resultMap="baseUesr">SELECTuser_id,user_username,user_create_datetime,user_genderFROMuser<where><choose><when test="username != nulll">user_username = #{username}</when> <when test="gender != null">user_gender = #{gender}</when><otherwise>1 = 1</otherwise></choose></where>
</select>

5.3 set

  • 一个条件都不满足时， SQL 会是错误状态：拿条件列去做一个更新

  • Mapper.xml

<update id="update" parameterType="User">UPDATE user<set><if test="id != null">user_id = #{id},</if><if test="username != null">user_username = #{username},</if></set>WHERE user_id = #{id}
</update>

5.4 foreach

  • **foreach 用于遍历集合或数组 比如 in 查询 | 批量插入 **

  • UserMapper.java

package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.User;import java.util.List;@Mapper
public interface UserMapper {User selectById(int id);int updateGenderById(@Param("gender") String gender,@Param("id") int id);User selectByCondition(User user);User selectByOnlyOneCondition(User user);int update(User user);List<User> selectByIdList(List<Integer> ids);int insertBatch(List<User> userList);
}
  • Mapper.xml
<select id="selectByIdList" parameterType="list" resultMap="baseUser">SELECTuser_id,user_username,user_create_datetime,user_genderFROMuserWHEREuser_id IN<foreach collection="list" item="itemId" separator=", " open="(" close=")">#{itemId}</foreach>
</select><insert id="insertBatch" parameterType="list">INSERT INTO user(user_id, user_name, user_create_datetime, user_gender) VALUES<foreach collection="list" item="user" separator=", ">(null, #{user.username}, #{user.createDatetime}, #{user.gender})</foreach>	
</insert>

5.5 script

  • Java
@Update({"<script>","update Author","	<set>","		<if rest='username != null'>username=#{username}, </if>","		<if test='password != null>'password=#{password}, </if>","		<if test='email != null'>email=#{email}, </if>","		<if test='bio != null'>bio=#{bio}</if>,"   </set>","where id=#{id}","</script>"})void updateAuthorValues(Author author);

5.6 bind

  • 元素允许你在 OGNL 表达式以外创建一个变量，并将其绑定到当前的上下文
<select id="selectBlogsLike" resultType="Blog"><bind name="pattern" value="'%' + _parameter.getTitle() + '%'"/>SELECT * FROM BLOGWHERE title LIKE #{pattern}
</select>

5.7 ${}

  • ${} 为上下文表达式获取变量不转义, #{} 是 SQL 占位解析符放入变量会转义满足 SQL

  • #{} 是 SQL 占位符 是 Mybatis 自行实现的

  • 请参考类: org.apache.ibatis.builder.SqlSourceBuilder

  • UserMapper.java

package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.example.mybatis.entity.User;import java.util.List;@Mapper 
public interface UserMapper {String selectOneColumnOneValue(@Param("column") String column,@Param("id") int id);
}
  • UserMapper.xml
<select id="selectOneColumnOneValue" resultType="string">SELECT${column}FORMuserWHEREuser_id = #{id}
</select>

06.API

6.1 核心配置

  • Application.java
package org.example.mybatis.api;import org.apache.ibatis.datasource.pooled.PooledDataSource;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory;
import org.example.mybatis.entity.User;
import org.example.mybatis.mapper.UserMapper;public class Application {public static void main(String[] args) {JdbcTransactionFactory factory = new JdbcTransactionFactory();pooledDataSource dataSource = new PooledDataSource();String driver = "com.mysql.cj.jdbc.Driver";String url = "jdbc:mysql:///mybatis?serverTimezone=Asia/Shanghai";String username="root";String password="root";dataSource.setDriver(driver);dataSource.setUrl(url);dataSource.setUsername(username);dataSource.setPassword(password);Environment environment = new Environment("dev", factory, dataSource);Configuration configuration = new Configuration(environment);configuration.addMappers("org.example.mybatis.mapper");configuration.getTypeAliasRegistry().registerAliases("org.example.mybatis.entity");// configuration.addInterceptor();configuration.setCacheEnabled(true);SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);SqlSession sqlSession = sqlSessionFactory.openSession(true);UserMapper mapper = sqlSession.getMapper(UserMapper.class);// User user = mapper.selectById(3);// System.out.println(user);mapper.selectList().forEach(System.out::println);sqlSession.commit();}}

6.2 映射注解

Mybatis 提供 @Select | @Update @Result 用于完成对应 xml 的映射行为

  • User.java
package org.example.mybatis.entity;import lombok.Data;import java.time.LocalDateTime;@Data
public class User {private Integer id;private String username;private LocalDateTime createDatetime;private Gender gender;}public enum Gender {MAN("男"), WOMAN("女")；private final String gender;private Gender(String gender) {this.gender = gender;}public String getGender() {return gender;}
}
  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.ResultMap;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotaions.Select;
import org.example.mybatis.entity.User;import java.util.List;@Mapper
public interface UserMapper {@Select ("SELECTuser_id,user_username,user_create_datetime,user_genderFROMuserWHERE user_id = #{id}")@Results(id = "baseUser", value= {@Result(id = "true", column = "user_id", property = "id"),@Result(id = "user_username", property = "username"),@Result(column = "user_create_datetime", property = "createDatetime"),@Result(column = "user_gender", property = "gender")})User selectById(int id);@Select ("SELECTuser_id,user_username,user_create_datetime,FROMuser")@ResultMap("bassUser")List<User> selectList();
}

07.SQL构建器

Mybatis 提供 Java API 方式构建 SQL 语句

  • Demo
package org.example.mybatis.api;import org.apache.ibatis.jdbc.SQL;public class SqlBuilderUsage {public static void main(String[] args) {String SQL  = new SQL() {SELECT("user_id", "user_username");FROM("USER");WHERE("user_id = #{id}");}.toString();System.out.prinltn(SQL);}
}

08.分页插件

8.1 分页逻辑

当分页数据为全表数据或条件查询部分数据时, 可采用不同分页策略

01 全表
  • 当对全表数据进行分页时，可直接借助 ID 进行 SQL 逻辑分页
  • 页码: page = 1
  • SQL
page = 1SELECT *
FROMTABLE_NAME
WHEREid >= ((page - 1) * size) && id <= (page * size)
02 条件查询
  • 页码: page = 1 起始位置 = (page - 1) * size
  • SQL
SELECT *
FROMTABLE_NAME
WHERE查询条件 LIMIT startIndex, count
分页数据
  • 必须返回 总数据量， 总页码， 当前页码数据
  • 总数据量 = SELECT COUNT(*) FROM TABLE [WHERE 条件]
  • 总页码数 = 总数据量 / 每页数据量 [如果除不尽需要 + 1]

8.2 PageHelper

https://pagehelper.github.io/

01 概念
  1. PageHelper 是针对 Mybatis 框架的分页插件，同时也能适配各种数据库
  2. PageHelper 是通过 Mybatis 拦截器 拦截 SQL 并改变 SQL 来实现分页
  • 官网
02 环境
  • pom.xml
<!-- https://mvnrepository.com/artifact/com.github.pagehelper/pageheler -->
<dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>6.0.0</version>
</dependency>
  • dependency

image-20240927173114313

  • mysql
<!-- SQL: SELECT VERSION(): -->
<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version>
</dependency>
  • pom.xml [src/main/java 非java文件编译打包配置]
<build><resources><resource><directory>src/main/java</directory><includes><include>**/*.*</include></includes></resource><resource><directory>src/mian/resources</directory><includes><include>**/*.*</include></includes></resource></resources>
</build>
03 应用
  • GoodsMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.Goods;import java.util.List;@Mapper
public interface GoodsMapper {List<Goods> selectByTitleLikeKeyword(String keyword);}
  • s
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC"-//mybatis.org//DTD Mapper 3.0//EN"""https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.example.mybatis.mapper.GoodsMapper"><resultMap id="baseGoods" type="Goods"><id column="goods_id" property="id"/><result column="goods_url" property="url"/><result column="goods_title" property="title"/><result column="goods_type" property="type"/><result column="goods_price"property="price"/></resultMap><select id="selectByTitleLikeKeyword"parameterType="string"resultMap="baseGoods">SELECTgoods_id,goods_url,goods_title,goods_type,goods_priceFROMtb_goodsWHEREgoods_title LIKE CONCAT('%'，#{keyword}, '%'}</select>
</mapper>
  • Api
GoodsMapper mapper = sqlSession.getMapper(GoodsMapper.class);Page<Goods> page = PageHelper.startPage(5, 20)
mapper.selectByTitleLikeKeyWord("手机");// System.out.println("page.getPages() = " + page.getPages());
// System.out.println("page.getTotal() =" + page.getTotal());
// page.getResult().forEach(System.out::println);
  • mybatis-config.xml
<plugins><plugin interceptor="com.github.pagehelper.PageInterceptor"/>
</plugins>
  • Console

image-20240927180233319

09.权限模型实战

基于角色的控制权限 RBAC (Role-Based Access Control)

9.1 表

CREATE TABLE user (user_id			INT PRIMARY KEY AUTO_INCREMENT,user_username	VARCHAR(20)user_phone 		VARCHAR(20)...
)
CREATE TABLE role (role_id INT PRIMARY KEY AUTO_INCREMENT,role_name 	VARCHAR(20),
)
CREATE TABLE permission (permission_id INT PRIMARY KEY AUTO_INCREMENT,permission_name VARCHAR(20),
)
CREATE TABLE user_role (ur_id INT PRIMARY KEY AUTO_INCREMENT,ur_user_id INTur_role_id INT
)
CREATE TABLE role_permission (rp_id INT PRIMARY KEY AUTO_INCREMENT,rp_role_id 	INT,rp_permission_id	INT
)

9.2 实战

实体类

  • User.java
package org.example.mybatis.entity;import lombok.Data;@Data
public class User {private Integer id;private String username;private String phone;private Role role;
}
  • Roel.java
package org.example.mybatis.entity;import lombok.Data;import java.util.List;@Data
public class Role {private Integer id;private String name;private List<Permission> permissions;
}
  • Permission.java
package org.example.mybatis.entity;import lombok.Data;@Data
public class Permission {private Integer id;private String name;}

Mapper

  • UserMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.User;@Mapper
public interface UserMapper {User selectById(int id);}
  • UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="org.example.mybatis.mapper.UserMapper"><resultMap id="baseUser" type="User"><id column="user_id" property="id"/><result column="user_username" property="username"/><result column="user_phone" property="phone"/></resultMap><resultMap id="userAndRole" type="User" extends="baseUser"><association property="role"column="user_id"select="org.example.mybatis.mapper.RoleMapper.selectByUserId"fetchType="lazy"/></resultMap><select id="selectById" parameterType="_int" resultMap="userAndRole">SELECTuser_id,user_username,user_phoneFROMuserWHEREuser_id = #{id}</select></mapper>
  • RoleMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.Role;@Mapper
public interface RoleMapper {Role selectByUserId(int userId);}
  • RoleMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="org.example.mybatis.mapper.UserMapper"><resultMap id="baseRole" type="Role"><id column="role_id" property="id"/><result column="role_name" property="name"/></resultMap><resultMap id="roleAndPermission" type="Role" extends="baseRole"><association property="permissions"javaType="list"ofType="Permission"column="role_id"select="org.example.mybatis.mapper.PermissionMapper.selectListByRoleId"fetchType="lazy"/></resultMap><select id="selectByUserId" parameterType="_int" resultMap="roleAndPermission">SELECTR.role_id,R.role_nameFROMROLE RJOIN 	user_role URON		R.role_id = UR.ur_role_id AND UR.ur_user_id = #{userId}</select></mapper>
  • PermissionMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.Permission;import java.util.List;@Mapper
public interface PermissionMapper {List<Permission> selectListByRoleId(int roleId);}
  • PermissionMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="org.example.mybatis.mapper.UserMapper"><resultMap id="basePermission" type="Permission"><id column="permission_id" property="id"/><result column="permission_name" property="name"/></resultMap><select id="selectListByRoleId" parameterType="_int" resultMap="basePermission">SELECTP.permission_id,P.permission_nameFROMpermission PJOIN 	role_permission RPON		RP.rp_permission_id = P.permission_id AND RP.rp_role_id = #{roId}</select></mapper>
  • RoleMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="org.example.mybatis.mapper.UserMapper"><resultMap id="baseRole" type="Role"><id column="role_id" property="id"/><result column="role_name" property="name"/></resultMap><resultMap id="roleAndPermission" type="Role" extends="baseRole"><association property="permissions"javaType="list"ofType="Permission"column="role_id"select="org.example.mybatis.mapper.PermissionMapper.selectListByRoleId"fetchType="lazy"/></resultMap><select id="selectByUserId" parameterType="_int" resultMap="roleAndPermission">SELECTR.role_id,R.role_nameFROMROLE RJOIN 	user_role URON		R.role_id = UR.ur_role_id AND UR.ur_user_id = #{userId}</select></mapper>
  • PermissionMapper.java
package org.example.mybatis.mapper;import org.apache.ibatis.annotations.Mapper;
import org.example.mybatis.entity.Permission;import java.util.List;@Mapper
public interface PermissionMapper {List<Permission> selectListByRoleId(int roleId);}
  • PermissionMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""https://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="org.example.mybatis.mapper.UserMapper"><resultMap id="basePermission" type="Permission"><id column="permission_id" property="id"/><result column="permission_name" property="name"/></resultMap><select id="selectListByRoleId" parameterType="_int" resultMap="basePermission">SELECTP.permission_id,P.permission_nameFROMpermission PJOIN 	role_permission RPON		RP.rp_permission_id = P.permission_id AND RP.rp_role_id = #{roId}</select></mapper>

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