MyBatis之注解开发

ゝ一纸荒年。 2024-03-22 18:50 51阅读 0赞

除了XML映射方式，MyBatis还支持注解方式实现POJO对象和数据表之间的关联映射，使用注解的方式一般将SQL语句直接写到接口上。与XML的映射方式相比，基于注解的映射方式相对简单。Mybatis提供的注解有：  
![在这里插入图片描述][d43a7091b718490c9ee9646708cd3e5f.png]

## 1.环境准备 ##

### 1.1 数据库准备 ###

USE mybatis;
    # 创建一个名称为tb_worker的表
    CREATE TABLE  tb_worker( 
         id INT PRIMARY KEY AUTO_INCREMENT,
         name VARCHAR(32),
         age INT,
         sex VARCHAR(8),
         worker_id INT UNIQUE     
    );
    # 插入2条数据
    INSERT INTO tb_worker(name,age,sex,worker_id)VALUES('张三',32,'女',1001);
    INSERT INTO tb_worker(name,age,sex,worker_id)VALUES('李四',29,'男',1002);
    INSERT INTO tb_worker(name,age,sex,worker_id)VALUES('王五',26,'男',1003);

### 1.2 Idea基础环境 ###

#### 1.2.1 创建annotaion module ####

![在这里插入图片描述][aff767d079e149709425d572348111c1.png]

#### 1.2.2 pom.xml引入依赖 ####

<?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">
        <parent>
            <artifactId>mybatis-series</artifactId>
            <groupId>com.biem</groupId>
            <version>1.0-SNAPSHOT</version>
        </parent>
        <modelVersion>4.0.0</modelVersion>
    
        <artifactId>annotation</artifactId>
    
        <properties>
            <maven.compiler.source>8</maven.compiler.source>
            <maven.compiler.target>8</maven.compiler.target>
        </properties>
    
        <dependencies>
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.4.6</version>
            </dependency>
    
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>8.0.18</version>
            </dependency>
    
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
                <scope>test</scope>
            </dependency>
    
            <dependency>
                <groupId>log4j</groupId>
                <artifactId>log4j</artifactId>
                <version>1.2.16</version>
            </dependency>
    
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <version>1.18.16</version>
            </dependency>
        </dependencies>
    </project>

#### 1.2.3 创建资源 ####

##### 包：4个 #####

###### (1) src/main/java下创建 ######

com.biem.pojo  
com.biem.mapper  
com.biem.util

###### (2) src/test/java下创建 ######

##### 类：4个 #####

###### (1) com.biem.pojo.Worker.java ######

package com.biem.pojo;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    import lombok.Getter;
    import lombok.NoArgsConstructor;
    
    /**
     * ClassName: Worker
     * Package: com.biem.pojo
     * Description:
     *
     * @Create 2023/5/19 8:27
     * @Version 1.0
     */
    @Data
    //@Data ： 注在类上，提供类的get、set、equals、hashCode、canEqual、toString方法
    @NoArgsConstructor
    @AllArgsConstructor
    public class Worker {
        
        private Integer id;
        private String name;
        private Integer age;
        private String sex;
        private Integer workerId;
    }

###### (2) com.biem.mapper.WorkerMapper.java ######

package com.biem.mapper;
    
    /**
     * ClassName: WorkerMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 8:27
     * @Version 1.0
     */
    public interface WorkerMapper {
        
    }

###### (3) com.biem.util.MyBatisUtil.java ######

package com.biem.util;
    
    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 java.io.IOException;
    import java.io.InputStream;
    
    /**
     * ClassName: MybatisUtil
     * Package: com.biem.util
     * Description:
     *
     * @Create 2023/4/5 22:23
     * @Version 1.0
     */
    public class MyBatisUtil {
        
        //利用static(静态)属于类不属于对象,且全局唯一
        private static SqlSessionFactory sqlSessionFactory = null;
        //利用静态块在初始化类时实例化sqlSessionFactory
        static {
        
            InputStream is= null;
            try {
        
                is = Resources.getResourceAsStream("mybatis-config.xml");
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
            } catch (IOException e) {
        
                e.printStackTrace();
                throw new ExceptionInInitializerError(e);
            }
        }
    
        /**
         * openSession 创建一个新的SqlSession对象
         * @return SqlSession对象
         */
        public static SqlSession openSession(boolean autoCommit){
        
            return sqlSessionFactory.openSession(autoCommit);
        }
    
        public static SqlSession openSession(){
        
            return sqlSessionFactory.openSession();
        }
        /**
         * 释放一个有效的SqlSession对象
         * @param session 准备释放SqlSession对象
         */
        public static void closeSession(SqlSession session){
        
            if(session != null){
        
                session.close();
            }
        }
    }

###### (4) com.biem.test.WorkerTest.java ######

package com.biem.test;
    
    /**
     * ClassName: WorkerTest
     * Package: com.biem.test
     * Description:
     *
     * @Create 2023/5/19 9:21
     * @Version 1.0
     */
    public class WorkerTest {
        
    }

##### 配置：3个 #####

###### (1) jdbc.properties ######

jdbc.driver=com.mysql.cj.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC
    jdbc.username=root
    jdbc.password=root

###### (2) log4j.xml ######

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
    
    <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
    
        <appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
            <param name="Encoding" value="UTF-8"/>
            <layout class="org.apache.log4j.PatternLayout">
                <param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n"/>
            </layout>
        </appender>
        <logger name="java.sql">
            <level value="debug"/>
        </logger>
        <logger name="org.apache.ibatis">
            <level value="info"/>
        </logger>
        <root>
            <level value="debug"/>
            <appender-ref ref="STDOUT"/>
        </root>
    </log4j:configuration>

###### (3) mybatis-config.xml ######

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
            PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
        
        <properties resource="jdbc.properties"></properties>
    
        
        <settings>
            <setting name="mapUnderscoreToCamelCase" value="true"/>
        </settings>
    
        
        <typeAliases>
            <package name="com.biem.pojo"/>
        </typeAliases>
    
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"/>
                <dataSource type="POOLED">
                    <property name="driver" value="${jdbc.driver}"/>
                    <property name="url" value="${jdbc.url}"/>
                    <property name="username" value="${jdbc.username}"/>
                    <property name="password" value="${jdbc.password}"/>
                </dataSource>
            </environment>
    
        </environments>
    
        
        <mappers>
            <package name="com.biem.mapper"/>
        </mappers>
    
    </configuration>

## 2.常用注解 ##

### 2.1 @Select注解 ###

#### 2.1.1 com.biem.mapper.WorkerMapper.java下添加 ####

@Select("select * from tb_worker where id=#{id}")
        public Worker findWorkerById(Integer id);

#### 2.1.2 com.biem.test.WorkerTest.java下添加 ####

@Test
        public void findWorkerById(){
        
            SqlSession session = MyBatisUtil.openSession();
            WorkerMapper mapper = session.getMapper(WorkerMapper.class);
            System.out.println("mapper.findWorkerById(1) = " + mapper.findWorkerById(1));
            session.close();
        }

#### 2.1.3 输出结果 ####

DEBUG 05-19 10:14:56,714 ==>  Preparing: select * from tb_worker where id=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:14:56,800 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:14:56,863 <==      Total: 1 (BaseJdbcLogger.java:159) 
    mapper.findWorkerById(1) = Worker(id=1, name=张三, age=32, sex=女, workerId=1001)

### 2.2 @Insert注解 ###

#### 2.2.1 com.biem.mapper.WorkerMapper.java下添加 ####

@Insert("insert into tb_worker(name, age, sex, worker_id) values(#{name}, #{age}, #{sex}, #{workerId})")
        public int insertWorker(Worker worker);

#### 2.2.2 com.biem.test.WorkerTest.java下添加 ####

@Test
        public void inserWorker(){
        
            SqlSession session = MyBatisUtil.openSession();
            WorkerMapper mapper = session.getMapper(WorkerMapper.class);
            Worker worker = new Worker();
            worker.setName("王强");
            worker.setAge(36);
            worker.setSex("女");
            worker.setWorkerId(1004);
            int result = mapper.insertWorker(worker);
            session.commit();
            session.close();
        }

#### 2.2.3 输出结果 ####

DEBUG 05-19 10:27:51,392 ==>  Preparing: insert into tb_worker(name, age, sex, worker_id) values(?, ?, ?, ?)  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:27:51,472 ==> Parameters: 王强(String), 36(Integer), 女(String), 1004(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:27:51,477 <==    Updates: 1 (BaseJdbcLogger.java:159)

### 2.3 @Update注解 ###

#### 2.3.1 com.biem.mapper.WorkerMapper.java下添加 ####

@Update("update tb_worker set name=#{name},age=#{age} where id = #{id}")
        public int updateWorker(Worker worker);

#### 2.3.2 com.biem.test.WorkerTest.java下添加 ####

@Test
        public void updateWorker(){
        
            SqlSession session = MyBatisUtil.openSession();
            WorkerMapper mapper = session.getMapper(WorkerMapper.class);
            Worker worker = new Worker();
            worker.setId(4);
            worker.setName("王冰");
            worker.setAge(36);
            int result = mapper.updateWorker(worker);
            if(result>0){
        
                System.out.println("更新了"+result+"条数据");
            } else {
        
                System.out.println("更新失败");
            }
            session.commit();
            session.close();
        }

#### 2.3.3 输出结果 ####

DEBUG 05-19 10:40:23,577 ==>  Preparing: update tb_worker set name=?,age=? where id = ?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:40:23,640 ==> Parameters: 王冰(String), 36(Integer), 4(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:40:23,645 <==    Updates: 1 (BaseJdbcLogger.java:159) 
    更新了1条数据

### 2.4 @Delete注解 ###

#### 2.4.1 com.biem.mapper.WorkerMapper.java下添加 ####

@Delete("delete from tb_worker where id=#{id}")
        public int deleteWorkerById(Integer id);

#### 2.4.2 com.biem.test.WorkerTest.java下添加 ####

@Test
        public void deleteWorkerById(){
        
            SqlSession session = MyBatisUtil.openSession();
            WorkerMapper mapper = session.getMapper(WorkerMapper.class);
            int result = mapper.deleteWorkerById(4);
            if(result>0){
        
                System.out.println("删除了"+result+"条数据");
            } else {
        
                System.out.println("删除失败");
            }
            session.close();
        }

#### 2.4.3 输出结果 ####

DEBUG 05-19 10:43:44,179 ==>  Preparing: delete from tb_worker where id=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:43:44,247 ==> Parameters: 4(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 10:43:44,251 <==    Updates: 1 (BaseJdbcLogger.java:159) 
    删除了1条数据

### 2.5 @Param注解 ###

@Param注解的作用是指定SQL语句中的参数，通常用于SQL语句中参数比较多的情况。

#### 2.4.1 com.biem.mapper.WorkerMapper.java下添加 ####

//mybatis不能识别多个参数,所以多个参数会抛出，
        //Cause: org.apache.ibatis.binding.BindingException: Parameter 'id' not found. Available parameters are [arg1, arg0, param1, param2]
        @Select("select * from tb_worker where id=#{id} and name=#{name}")
        public Worker findWorkerByIdAndName1(Integer id, String name);
    
        @Select("select * from tb_worker where id=#{param1} and name=#{param2}")
        public Worker findWorkerByIdAndName2(@Param("param1") Integer id, @Param("param2") String name);
    
        @Select("select * from tb_worker where id=#{arg1} and name=#{arg0}")
        public Worker findWorkerByIdAndName3(@Param("arg1") Integer id, @Param("arg0") String name);

#### 2.4.2 com.biem.test.WorkerTest.java下添加 ####

@Test
        public void findWorkerByIdAndName1(){
        
            SqlSession session = MyBatisUtil.openSession();
            WorkerMapper mapper = session.getMapper(WorkerMapper.class);
            System.out.println("mapper.findWorkerByIdAndName1(1,\"张三\") = " + mapper.findWorkerByIdAndName1(1, "张三"));
            session.close();
        }
    
        @Test
        public void findWorkerByIdAndName2(){
        
            SqlSession session = MyBatisUtil.openSession();
            WorkerMapper mapper = session.getMapper(WorkerMapper.class);
            System.out.println("mapper.findWorkerByIdAndName2(1,\"张三\") = " + mapper.findWorkerByIdAndName2(1, "张三"));
            session.close();
        }
    
        @Test
        public void findWorkerByIdAndName3(){
        
            SqlSession session = MyBatisUtil.openSession();
            WorkerMapper mapper = session.getMapper(WorkerMapper.class);
            System.out.println("mapper.findWorkerByIdAndName3(1,\"张三\") = " + mapper.findWorkerByIdAndName3(1, "张三"));
            session.close();
        }

#### 2.4.3 输出结果 ####

##### (1) findWorkerByIdAndName1结果 #####

org.apache.ibatis.exceptions.PersistenceException: 
    ### Error querying database.  Cause: org.apache.ibatis.binding.BindingException: Parameter 'id' not found. Available parameters are [arg1, arg0, param1, param2]
    ### Cause: org.apache.ibatis.binding.BindingException: Parameter 'id' not found. Available parameters are [arg1, arg0, param1, param2]
    
    	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
    	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150)
    	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
    	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77)
    	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:83)
    	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:59)
    	at com.sun.proxy.$Proxy9.findWorkerByIdAndName1(Unknown Source)
    	at com.biem.test.WorkerTest.findWorkerByIdAndName1(WorkerTest.java:79)
    	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    	at java.lang.reflect.Method.invoke(Method.java:498)
    	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
    	at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38)
    	at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11)
    	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35)
    	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
    	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
    Caused by: org.apache.ibatis.binding.BindingException: Parameter 'id' not found. Available parameters are [arg1, arg0, param1, param2]
    	at org.apache.ibatis.binding.MapperMethod$ParamMap.get(MapperMethod.java:204)
    	at org.apache.ibatis.reflection.wrapper.MapWrapper.get(MapWrapper.java:45)
    	at org.apache.ibatis.reflection.MetaObject.getValue(MetaObject.java:122)
    	at org.apache.ibatis.executor.BaseExecutor.createCacheKey(BaseExecutor.java:219)
    	at org.apache.ibatis.executor.CachingExecutor.createCacheKey(CachingExecutor.java:146)
    	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:82)
    	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
    	... 30 more

##### (2) findWorkerByIdAndName2结果 #####

DEBUG 05-19 14:21:20,200 ==>  Preparing: select * from tb_worker where id=? and name=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:21:20,280 ==> Parameters: 1(Integer), 张三(String) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:21:20,334 <==      Total: 1 (BaseJdbcLogger.java:159) 
    mapper.findWorkerByIdAndName2(1,"张三") = Worker(id=1, name=张三, age=32, sex=女, workerId=1001)

##### (3) findWorkerByIdAndName3结果 #####

DEBUG 05-19 14:23:33,639 ==>  Preparing: select * from tb_worker where id=? and name=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:23:33,703 ==> Parameters: 1(Integer), 张三(String) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:23:33,754 <==      Total: 1 (BaseJdbcLogger.java:159) 
    mapper.findWorkerByIdAndName3(1,"张三") = Worker(id=1, name=张三, age=32, sex=女, workerId=1001)

## 3.基于注解的关联查询 ##

MyBatis注解不仅仅可以实现增删改查，MyBatis还提供了一系列注解@Results、@Result、@One、@Many等注解实现关联查询。

### 3.1 一对一查询 ###

MyBatis使用@One注解实现数据表的一对一查询

#### 3.1.1 环境准备 ####

##### 3.1.1.1 数据库准备 #####

USE mybatis;
    # 创建一个名称为tb_idcard的表
    CREATE TABLE  tb_idcard( 
         id INT PRIMARY KEY AUTO_INCREMENT,
         CODE VARCHAR(18)
    );
    # 插入2条数据
    INSERT INTO tb_idcard(CODE) VALUES('152221198711020624');
    INSERT INTO tb_idcard(CODE) VALUES('152201199008150317');
    # 创建一个名称为tb_person的表
    CREATE TABLE tb_person( 
         id INT PRIMARY KEY AUTO_INCREMENT,
         name VARCHAR(32),
         age INT,
         sex VARCHAR(8),
         card_id INT UNIQUE,     
         FOREIGN KEY(card_id) REFERENCES tb_idcard(id)
    );
    # 插入2条数据
    INSERT INTO tb_person(name,age,sex,card_id) VALUES('Rose',22,'女',1);
    INSERT INTO tb_person(name,age,sex,card_id) VALUES('jack',23,'男',2);

##### 3.1.1.2 实体类准备 #####

###### 3.1.1.2.1 IdCard.java ######

package com.biem.pojo;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    import lombok.NoArgsConstructor;
    
    /**
     * ClassName: IdCard
     * Package: com.biem.pojo
     * Description:
     *
     * @Create 2023/5/19 14:44
     * @Version 1.0
     */
    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public class IdCard {
        
        private Integer id;                 //主键id
        private String code;                //身份证号码
    }

###### 3.1.1.2.2 Person.java ######

package com.biem.pojo;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    import lombok.NoArgsConstructor;
    
    /**
     * ClassName: Person
     * Package: com.biem.pojo
     * Description:
     *
     * @Create 2023/5/19 14:44
     * @Version 1.0
     */
    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public class Person {
        
        private Integer id;          //主键id
        private String name;         //姓名
        private Integer age;         //年龄
        private String sex;          //性别
        private IdCard card;        //人员关联的证件
    }

##### 3.1.1.3 接口类准备 #####

###### 3.1.1.3.1 IdCardMapper.java ######

package com.biem.mapper;
    
    /**
     * ClassName: IdCardMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 14:48
     * @Version 1.0
     */
    public interface IdCardMapper {
        
    }

###### 3.1.1.3.2 PersonMapper.java ######

package com.biem.mapper;
    
    /**
     * ClassName: PersonMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 14:49
     * @Version 1.0
     */
    public interface PersonMapper {
        
    }

#### 3.1.2 案例测试 ####

根据id查询 Peson对象

#### 3.1.2.1 接口类添加 ####

##### 3.1.2.1.1 IdCardMapper.java #####

@Select("select * from tb_idcard where id=#{id}")
        public IdCard findIdCardById(int id);

##### 3.1.2.1.2 PersonMapper.java #####

@Select("select * from tb_person where id=#{id}")
        @Results(
                {
        @Result(column = "card_id",
                         property = "card",
                         one = @One(select = "com.biem.mapper.IdCardMapper.findIdCardById"))})
        Person findPersonById(int id);

#### 3.1.2.2 添加测试类 ####

com.biem.test.PersonTest.java

package com.biem.test;
    
    import com.biem.mapper.PersonMapper;
    import com.biem.pojo.Person;
    import com.biem.util.MyBatisUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    /**
     * ClassName: PersonTest
     * Package: com.biem.test
     * Description:
     *
     * @Create 2023/5/19 14:54
     * @Version 1.0
     */
    public class PersonTest {
        
    
        @Test
        public void findPersonById(){
        
            SqlSession session = MyBatisUtil.openSession();
            PersonMapper mapper = session.getMapper(PersonMapper.class);
            Person person = mapper.findPersonById(1);
            System.out.println("person = " + person);
            session.close();
        }
    }

#### 3.1.2.3 运行结果 ####

DEBUG 05-19 14:57:14,273 ==>  Preparing: select * from tb_person where id=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:57:14,372 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:57:14,421 ====>  Preparing: select * from tb_idcard where id=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:57:14,421 ====> Parameters: 1(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:57:14,440 <====      Total: 1 (BaseJdbcLogger.java:159) 
    DEBUG 05-19 14:57:14,443 <==      Total: 1 (BaseJdbcLogger.java:159) 
    person = Person(id=1, name=Rose, age=22, sex=女, card=IdCard(id=1, code=152221198711020624))

### 3.2 一对多查询 ###

MyBatis使用@Many注解实现数据表的一对多关联查询，@Many注解的作用等同于XML配登文件中的元素。

#### 3.2.1 环境准备 ####

##### 3.2.1.1 数据库准备 #####

USE mybatis;
    # 创建一个名称为tb_user的表
    CREATE TABLE tb_user (
      id int(32) PRIMARY KEY AUTO_INCREMENT,
      username varchar(32),
      address varchar(256)
     );
    # 插入3条数据
    INSERT INTO tb_user VALUES ('1', '小明', '北京');
    INSERT INTO tb_user VALUES ('2', '李华', '上海');
    INSERT INTO tb_user VALUES ('3', '李刚', '上海');
    # 创建一个名称为tb_orders的表
    CREATE TABLE tb_orders (
      id int(32) PRIMARY KEY AUTO_INCREMENT,
      number varchar(32) NOT NULL,
      user_id int(32) NOT NULL,
      FOREIGN KEY(user_id) REFERENCES tb_user(id)
    );
    # 插入3条数据
    INSERT INTO tb_orders VALUES ('1', '1000011', '1');
    INSERT INTO tb_orders VALUES ('2', '1000012', '1');
    INSERT INTO tb_orders VALUES ('3', '1000013', '2');

##### 3.2.1.2 实体类准备 #####

###### 3.2.1.2.2 Orders.java ######

package com.biem.pojo;
    
    /**
     * ClassName: Orders
     * Package: com.biem.pojo
     * Description:
     *
     * @Create 2023/5/19 15:09
     * @Version 1.0
     */
    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public class Orders {
        
        private Integer id;                //订单id
        private String number;            //订单编号
    }

###### 3.2.1.2.2 User.java ######

import lombok.NoArgsConstructor;
    
    /**
     * ClassName: User
     * Package: com.biem.pojo
     * Description:
     *
     * @Create 2023/5/19 15:05
     * @Version 1.0
     */
    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public class User {
        
        private Integer id;                 // 用户编号
        private String username;           // 用户姓名
        private String address;            // 用户地址
        private List<Orders> ordersList; //用户关联的订单
    }

##### 3.2.1.3 接口类准备 #####

###### 3.2.1.3.1 UserMapper.java ######

package com.biem.mapper;
    
    /**
     * ClassName: UserMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 15:11
     * @Version 1.0
     */
    public interface UserMapper {
        
    }

###### 3.2.1.3.2 OrdersMapper.java ######

package com.biem.mapper;
    
    /**
     * ClassName: OrdersMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 15:11
     * @Version 1.0
     */
    public interface OrdersMapper {
        
    }

#### 3.2.2 案例测试 ####

##### 3.2.2.1 接口类添加 #####

##### 3.2.2.1.1 OrdersMapper.java #####

@Select("select * from tb_orders where user_id=#{id} ")
        @Results({
        @Result(id = true, column = "id", property = "id"),
                @Result(column = "number", property = "number")
        })
        public List<Orders> findOrdersByUserId(int user_id);

##### 3.2.2.1.2 UserMapper.java #####

@Select("select * from tb_user where id=#{id} ")
        @Results({
        @Result(id = true, column = "id", property = "id"),
                @Result(column = "username", property = "username"),
                @Result(column = "address", property = "address"),
                @Result(column = "id", property = "ordersList",
                        many = @Many(select =
                                "com.biem.mapper.OrdersMapper.findOrdersByUserId"))})
        User findUserById(int id);

##### 3.2.2.2 测试类添加 #####

package com.biem.test;
    
    import com.biem.mapper.UserMapper;
    import com.biem.pojo.User;
    import com.biem.util.MyBatisUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    /**
     * ClassName: UserTest
     * Package: com.biem.test
     * Description:
     *
     * @Create 2023/5/19 15:16
     * @Version 1.0
     */
    public class UserTest {
        
    
        @Test
        public void findUserById(){
        
            SqlSession session = MyBatisUtil.openSession();
            UserMapper mapper = session.getMapper(UserMapper.class);
            User user = mapper.findUserById(1);
            System.out.println("user = " + user);
            session.close();
        }
    }

##### 3.2.2.3 结果输出 #####

DEBUG 05-19 15:20:50,932 ==>  Preparing: select * from tb_user where id=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:20:51,004 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:20:51,056 ====>  Preparing: select * from tb_orders where user_id=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:20:51,056 ====> Parameters: 1(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:20:51,060 <====      Total: 2 (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:20:51,064 <==      Total: 1 (BaseJdbcLogger.java:159) 
    user = User(id=1, username=小明, address=北京, ordersList=[Orders(id=1, number=1000011), Orders(id=2, number=1000012)])

### 3.3 多对多查询 ###

表与表之间的多对多关联关系通常使用一个中间表来维护,tb\_orders和商品表 tb\_product为例，这两个表之间的关联关系使用了一个中间表 b\_ordersitem 来维护，需要数据库的三个表格

#### 3.3.1 环境准备 ####

##### 3.3.1.1 数据库准备 #####

USE mybatis;
    
    CREATE TABLE tb_orders (
      id int(32) PRIMARY KEY AUTO_INCREMENT,
      number varchar(32) NOT NULL,
      user_id int(32) NOT NULL,
      FOREIGN KEY(user_id) REFERENCES tb_user(id)
    );
    # 插入3条数据
    INSERT INTO tb_orders VALUES ('1', '1000011', '1');
    INSERT INTO tb_orders VALUES ('2', '1000012', '1');
    INSERT INTO tb_orders VALUES ('3', '1000013', '2');
    
    # 创建一个名称为tb_product的表
    CREATE TABLE tb_product (
      id INT(32) PRIMARY KEY AUTO_INCREMENT,
      NAME VARCHAR(32),
      price DOUBLE 
     );
    # 插入3条数据
    INSERT INTO tb_product VALUES ('1', 'Java基础入门', '44.5');
    INSERT INTO tb_product VALUES ('2', 'Java Web程序开发入门', '38.5');
    INSERT INTO tb_product VALUES ('3', 'SSM框架整合实战', '50');
    # 创建一个名称为tb_ordersitem 的中间表
    CREATE TABLE tb_ordersitem (
        id INT(32) PRIMARY KEY AUTO_INCREMENT,
        orders_id INT(32),
        product_id INT(32),
        FOREIGN KEY(orders_id) REFERENCES tb_orders(id),
    FOREIGN KEY(product_id) REFERENCES tb_product(id)
    );
    # 插入3条数据
    INSERT INTO tb_ordersitem  VALUES ('1', '1', '1');
    INSERT INTO tb_ordersitem  VALUES ('2', '1', '3');
    INSERT INTO tb_ordersitem  VALUES ('3', '3', '3');

##### 3.3.1.2 实体类准备 #####

Product.java

package com.biem.pojo;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    import lombok.NoArgsConstructor;
    
    import java.util.List;
    
    /**
     * ClassName: Product
     * Package: com.biem.pojo
     * Description:
     *
     * @Create 2023/5/19 15:26
     * @Version 1.0
     */
    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public class Product {
        
        private Integer id;                //商品id
        private String name;                //商品名称
        private Double price;                //商品单价
        private List<Orders> orders;        //与订单关联的属性
    }

Orders.java修改为

package com.biem.pojo;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    import lombok.NoArgsConstructor;
    
    import java.util.List;
    
    /**
     * ClassName: Orders
     * Package: com.biem.pojo
     * Description:
     *
     * @Create 2023/5/19 15:09
     * @Version 1.0
     */
    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public class Orders {
        
        private Integer id;                //订单id
        private String number;            //订单编号
        //关联商品集合属性
        private List<Product> productList;
    }

##### 3.3.1.1 接口类准备 #####

###### 3.3.1.1.1 OrdersMapper.java为以下代码，暂时不用修改 ######

package com.biem.mapper;
    
    import com.biem.pojo.Orders;
    import org.apache.ibatis.annotations.Result;
    import org.apache.ibatis.annotations.Results;
    import org.apache.ibatis.annotations.Select;
    
    import java.util.List;
    
    /**
     * ClassName: OrdersMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 15:11
     * @Version 1.0
     */
    public interface OrdersMapper {
        
    
        @Select("select * from tb_orders where user_id=#{id} ")
        @Results({
        @Result(id = true, column = "id", property = "id"),
                @Result(column = "number", property = "number")
        })
        public List<Orders> findOrdersByUserId(int user_id);
    }

###### 3.3.1.1.2 ProductMapper.java ######

package com.biem.mapper;
    
    /**
     * ClassName: ProductMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 15:28
     * @Version 1.0
     */
    public interface ProductMapper {
        
    }

#### 3.3.2 案例测试 ####

##### 3.3.2.1 接口类添加 #####

###### 3.3.2.1.1 ProductMapper.java修改 ######

package com.biem.mapper;
    
    import com.biem.pojo.Product;
    import org.apache.ibatis.annotations.Select;
    
    import java.util.List;
    
    /**
     * ClassName: ProductMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 15:28
     * @Version 1.0
     */
    public interface ProductMapper {
        
        @Select("select * from tb_product where id in (select product_id from " +
                "tb_ordersitem where orders_id = #{id} )")
        public List<Product> findProductByOrdersId(int orders_id);
    }

###### 3.3.2.1.2 OrdersMapper修改为 ######

package com.biem.mapper;
    
    import com.biem.pojo.Orders;
    import org.apache.ibatis.annotations.Many;
    import org.apache.ibatis.annotations.Result;
    import org.apache.ibatis.annotations.Results;
    import org.apache.ibatis.annotations.Select;
    
    import java.util.List;
    
    /**
     * ClassName: OrdersMapper
     * Package: com.biem.mapper
     * Description:
     *
     * @Create 2023/5/19 15:11
     * @Version 1.0
     */
    public interface OrdersMapper {
        
    
        @Select("select * from tb_orders where user_id=#{id} ")
        @Results({
        @Result(id = true, column = "id", property = "id"),
                @Result(column = "number", property = "number")
        })
        public List<Orders> findOrdersByUserId(int user_id);
    
    
        @Select("select * from tb_orders where id=#{id} ")
        @Results({
        @Result(id = true, column = "id", property = "id"),
                @Result(column = "number", property = "number"),
                @Result(column = "id", property = "productList",
                        many = @Many(select =
                                "com.biem.mapper.ProductMapper.findProductByOrdersId"))})
        public Orders findOrdersById(int id);
    }

##### 3.3.2.2 测试类添加 #####

package com.biem.test;
    
    import com.biem.mapper.OrdersMapper;
    import com.biem.pojo.Orders;
    import com.biem.util.MyBatisUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    /**
     * ClassName: OrdersTest
     * Package: com.biem.test
     * Description:
     *
     * @Create 2023/5/19 15:32
     * @Version 1.0
     */
    public class OrdersTest {
        
        @Test
        public void findOrdersById(){
        
            SqlSession session = MyBatisUtil.openSession();
            OrdersMapper mapper = session.getMapper(OrdersMapper.class);
            Orders orders = mapper.findOrdersById(1);
            System.out.println("orders = " + orders);
            session.close();
        }
    }

##### 3.3.2.3 结果输出 #####

DEBUG 05-19 15:34:18,076 ==>  Preparing: select * from tb_orders where id=?  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:34:18,147 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:34:18,192 ====>  Preparing: select * from tb_product where id in (select product_id from tb_ordersitem where orders_id = ? )  (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:34:18,192 ====> Parameters: 1(Integer) (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:34:18,217 <====      Total: 2 (BaseJdbcLogger.java:159) 
    DEBUG 05-19 15:34:18,217 <==      Total: 1 (BaseJdbcLogger.java:159) 
    orders = Orders(id=1, number=1000011, productList=[Product(id=1, name=Java基础入门, price=44.5, orders=null), Product(id=3, name=SSM框架整合实战, price=50.0, orders=null)])

[d43a7091b718490c9ee9646708cd3e5f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/18/465539f7fbc8456bbeb103cd9807a116.png
[aff767d079e149709425d572348111c1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/18/4a4cd8b36e294114a291004eb69419ed.png