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：
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
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>
<!--引入properties文件-->
<properties resource="jdbc.properties"></properties>
<!--将下划线映射为驼峰-->
<settings>
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!--设置类型别名-->
<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>
<!-- 引入映射文件 -->
<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)])