Mybatis一对多的关系

拼搏现实的明天。 2022-04-22 11:40 227阅读 0赞

前言：本项目是使用idea进行开发，数据库使用的是Mysql。  
province(一）----------city(多)  
![在这里插入图片描述][20181104214501749.png]  
![在这里插入图片描述][20181104214519152.png]  
**1.搭建maven项目,引入mybatis需要的依赖**  
默认没有java、resources、test等文件夹，习惯性建立这几个文件夹，建立文件夹的时候注意标记文件夹的用途（不然编译器无法识别，无法编译代码）  
pom.xml(注意要将实体包下面的xml文件设置可编译)

<?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>Mybatis_03</groupId>
      <artifactId>Mybatis_03</artifactId>
      <version>1.0-SNAPSHOT</version>
      <packaging>war</packaging>
    
      <name>Mybatis_03 Maven Webapp</name>
      
      <url>http://www.example.com</url>
    
      <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
      </properties>
    
      <dependencies>
        <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>4.12</version>
          <scope>test</scope>
        </dependency>
        
        <dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis</artifactId>
          <version>3.4.1</version>
        </dependency>
        
        <dependency>
          <groupId>mysql</groupId>
          <artifactId>mysql-connector-java</artifactId>
          <version>5.1.43</version>
        </dependency>
      </dependencies>
    
      <build>
        
        <resources>
          <resource>
            <directory>src/main/java</directory>
            <includes>
              <include>**/*.xml</include>
            </includes>
          </resource>
        </resources>
        <finalName>Mybatis_03</finalName>
        <pluginManagement>
          <plugins>
            <plugin>
              <artifactId>maven-clean-plugin</artifactId>
              <version>3.0.0</version>
            </plugin>
            
            <plugin>
              <artifactId>maven-resources-plugin</artifactId>
              <version>3.0.2</version>
            </plugin>
            <plugin>
              <artifactId>maven-compiler-plugin</artifactId>
              <version>3.7.0</version>
            </plugin>
            <plugin>
              <artifactId>maven-surefire-plugin</artifactId>
              <version>2.20.1</version>
            </plugin>
            <plugin>
              <artifactId>maven-war-plugin</artifactId>
              <version>3.2.0</version>
            </plugin>
            <plugin>
              <artifactId>maven-install-plugin</artifactId>
              <version>2.5.2</version>
            </plugin>
            <plugin>
              <artifactId>maven-deploy-plugin</artifactId>
              <version>2.8.2</version>
            </plugin>
          </plugins>
        </pluginManagement>
      </build>
    </project>

**2.项目模块图：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3plYWw5cw_size_16_color_FFFFFF_t_70]  
**3.在resources目录下新建mybatis的核心配置文件mybatis-config.xml**  
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>
        
        <typeAliases>
            <package name="com.zs.entity"/>
        </typeAliases>
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC" />
                
                <dataSource type="POOLED">
                    <property name="driver" value="com.mysql.jdbc.Driver" />
                    <property name="url" value="jdbc:mysql://localhost:3306/zs?characterEncoding=utf-8" />
                    <property name="username" value="root" />
                    <property name="password" value="1234" />
                </dataSource>
            </environment>
        </environments>
        <mappers>
            <mapper resource="com/zs/entity/City.xml"></mapper>
            <mapper resource="com/zs/entity/Province.xml"></mapper>
        </mappers>
    </configuration>

**4.建立与数据库对应的实体包，包下建立类与对应的xml文件（这里没有使用接口调用方法，是使用xml文件调用方法）**  
Province.java

package com.zs.entity;
    
    import java.util.List;
    
    /** * @author 小思 * @PackageName:com.zs.entity * @ClassName: Province * @Description:对应数据库Province表的实体类 * @date 2018/10/31 16:32 */
    public class Province { 
        private Integer pid;
        private String pname;
        private List<city> cities;
    
        public Province() { 
        }
    
        public Province(Integer pid) { 
            this.pid = pid;
        }
    
        public Province(String pname) { 
            this.pname = pname;
        }
    
        public Province(Integer pid, String pname) { 
            this.pid = pid;
            this.pname = pname;
        }
    
        public Province(Integer pid, String pname, List<city> cities) { 
            this.pid = pid;
            this.pname = pname;
            this.cities = cities;
        }
    
        public Integer getPid() { 
            return pid;
        }
    
        public void setPid(Integer pid) { 
            this.pid = pid;
        }
    
        public String getPname() { 
            return pname;
        }
    
        public void setPname(String pname) { 
            this.pname = pname;
        }
    
        public List<city> getCities() { 
            return cities;
        }
    
        public void setCities(List<city> cities) { 
            this.cities = cities;
        }
    }

city.java

package com.zs.entity;
    
    /** * @author 小思 * @PackageName:com.zs.entity * @ClassName: city * @Description:对应数据库City表的实体类 * @date 2018/10/31 16:33 */
    public class city { 
        private Integer cid;//城市的Id
        private String cname;//城市的名称
        private Province province;//城市所对应的省份
    
        public Integer getCid() { 
            return cid;
        }
    
        public void setCid(Integer cid) { 
            this.cid = cid;
        }
    
        public String getCname() { 
            return cname;
        }
    
        public void setCname(String cname) { 
            this.cname = cname;
        }
    
        public Province getProvince() { 
            return province;
        }
    
        public void setProvince(Province province) { 
            this.province = province;
        }
    
        public city() { 
        }
    
        public city(Integer cid) { 
            this.cid = cid;
        }
    
        public city(String cname) { 
            this.cname = cname;
        }
    
        public city(Integer cid, String cname) { 
            this.cid = cid;
            this.cname = cname;
        }
    
        public city(Integer cid, String cname, Province province) { 
            this.cid = cid;
            this.cname = cname;
            this.province = province;
        }
    
    }

Province.xml

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.zs.dao.ProvinceDao">
        
        <select id="getAllProvince" resultType="Province">
            select * from province
        </select>
    
        
        <select id="findCityById" resultType="city" parameterType="int">
            select * from city where pid=#{pid}
        </select>
    
    </mapper>

**5.在test文件夹下新建com.zs.test文件夹，并且新建单元测试类TestOneToMany.java**

package com.zs.test;
    
    import com.zs.dao.ProvinceDao;
    import com.zs.entity.city;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    import org.junit.After;
    import org.junit.Before;
    import org.junit.Test;
    
    import java.util.List;
    
    /** * @author 小思 * @PackageName:com.zs.test * @ClassName: TestOneToMany * @Description: * @date 2018/10/31 16:42 */
    @SuppressWarnings("unused")
    public class TestOneToMany { 
        SqlSessionFactory sessionFactory;
        SqlSession session;
    
        @Before
        public void before() { 
            //从mybatis-config.xml mybatis的核心配置文件中获取SqlSessionFactory
            sessionFactory = new SqlSessionFactoryBuilder().build(getClass().getClassLoader().getResourceAsStream("mybatis-config.xml"));
            //通过工厂获取SqlSession
            session = sessionFactory.openSession();
        }
    
    
        @Test
        public void testProvince() { 
            // 映射器是一个你创建来绑定你映射的语句的接口，调用合理描述参数和返回值的接口来获取相应的方法
            ProvinceDao pd = session.getMapper(ProvinceDao.class);
    
    // //查询所有的省份
    // List<Province> list = pd.getAllProvince();
    // for (Province p : list) { 
    // System.out.println(p.getPname());
    // }
    
            //根据省份的Id查询城市
            List<city> c=pd.findCityById(1);
            for (city city : c) { 
                System.out.println(city.getCname());
            }
    
    
        }
    
        @After
        public void after() { 
            //提交session和关闭session(释放无用资源)
            session.commit();
            session.close();
        }
    }

**6.测试时，取消注释，运行测试类即可**

**说在最后的话：编写实属不易，若喜欢或者对你有帮助记得点赞+关注或者收藏哦~**

[20181104214501749.png]: /images/20220422/ea42dcddb60f426aa5d9cd0f4c39128b.png
[20181104214519152.png]: /images/20220422/60969aaed17f47c4ac8e3ad893e0bfca.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3plYWw5cw_size_16_color_FFFFFF_t_70]: /images/20220422/0b5bef0b6cde4fc49f89cb3fb61678ce.png