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MyBatis笔记 | 详解MyBatis映射文件

MyBatis笔记 | 详解MyBatis映射文件

作者: 一颗白菜_ | 来源:发表于2019-11-28 21:52 被阅读0次

MyBatis映射文件

映射文件指导着MyBatis如何进行数据库增删改查，有着非常重要的意义，有以下标签：
cache：命名空间的二级缓存配置
cache-ref：其他命名空间缓存配置的引用
resultMap：自定义结果集映射
sql：抽取可重用语句块
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

简单的增删改查示例

注意的两点：

  • myBatis允许增删改查直接定义以下类型返回值：Integer、Long、Boolean、void。直接在接口的方法声明上修改返回值类型即可。
  • 如果在创建SqlSession时是使用sqlSessionFactory.openSession()的话我们需要手动提交数据，即sqlSession.commit()；如果使用的是sqlSessionFactory.openSession(true);则不需要手动提交，因为他会自动帮我们提交。

增删改查前的准备

我们有如下数据表：



对应的实体bean：

package com.cerr.mybatis;



public class Employee {
    private Integer id;
    private String lastName;
    private String email;
    private String gender;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                ", gender='" + gender + '\'' +
                '}';
    }

    public Employee(Integer id, String lastName, String email, String gender) {
        this.id = id;
        this.lastName = lastName;
        this.email = email;
        this.gender = gender;
    }

    public Employee() {
    }
}

定义接口的方法

我们需要在接口中定义增删改查的方法：

package com.cerr.mybatis.dao;

import com.cerr.mybatis.Employee;

public interface EmployeeMapper {
    //查
    public Employee getEmpById(Integer id);
    //增
    public boolean addEmp(Employee employee);
    //改
    public boolean updateEmp(Employee employee);
    //删
    public boolean deleteEmpById(Integer id);
}

配置sql映射文件

我们需要在sql映射文件中编写sql语句（sql映射文件和接口放在同一目录下）：

<?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.cerr.mybatis.dao.EmployeeMapper">
    <!-- 查 -->
    <select id="getEmpById" resultType="com.cerr.mybatis.Employee">
        select * from tb1_employee where id = #{id}
    </select>
    <!-- 增 -->
    <insert id="addEmp" parameterType="com.cerr.mybatis.Employee">
        insert into tb1_employee(last_name,email,gender) values(#{lastName},#{email},#{gender})
    </insert>
    <!-- 改 -->
    <update id="updateEmp">
        update tb1_employee set last_name = #{lastName},email=#{email},gender=#{gender}
            where id=#{id}
    </update>
    <!-- 删 -->
    <delete id="deleteEmpById">
        delete from tb1_employee where id = #{id}
    </delete>
</mapper>

将sql映射文件在全局配置文件中注册

<?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>
    <!-- 引入数据库信息资源文件 -->
    <properties resource="dbconfig.properties"></properties>
    
    <settings>
        <!-- 开启驼峰命名规则 -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

    <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>

    <!-- 将我们写好的sql映射文件注册到全局配置文件中 -->
    <mappers>
        <!-- 批量注册 -->
        <package name="com.cerr.mybatis.dao"/>
    </mappers>
</configuration>

1.测试新增数据

package com.cerr.mybatis;
import com.cerr.mybatis.dao.EmployeeMapper;
import com.cerr.mybatis.dao.EmployeeMapperAnnotation;
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.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import static org.junit.Assert.*;

public class MyBatisTest {
    //获取SQLSessionFactory
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    /**
     * 测试添加
     */
    @Test
    public void test3() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        //获取到的sql不会自动提交数据
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try{
            EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
            Employee employee = new Employee(null,"jerry","jerry@qq.com","1");
            Boolean isOk = mapper.addEmp(employee);
            //提交
            sqlSession.commit();
            System.out.println(isOk);
        }finally {
            sqlSession.close();
        }
    }
}

执行后结果如下：


数据库信息：


2.测试修改

我们将id=1的信息修改为last_name=aaa,email=aaa@qq.com,gender=1。
方法：

package com.cerr.mybatis;
import com.cerr.mybatis.dao.EmployeeMapper;
import com.cerr.mybatis.dao.EmployeeMapperAnnotation;
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.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import static org.junit.Assert.*;

public class MyBatisTest {
    //获取SQLSessionFactory
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

   /**
     * 测试修改
     */
    @Test
    public void test4() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        //获取到的sql不会自动提交数据
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try{
            EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
            Employee employee = new Employee(1,"aaa","aaa@qq.com","1");
            Boolean isOK = mapper.updateEmp(employee);
            //提交
            sqlSession.commit();
            if (isOK){
                System.out.println("修改成功，信息为:"+employee);
            }else{
                System.out.println("修改失败");
            }
        }finally {
            sqlSession.close();
        }
    }
}

控制台信息如下：



表：


3.测试删除

把id=3的记录给删除

package com.cerr.mybatis;
import com.cerr.mybatis.dao.EmployeeMapper;
import com.cerr.mybatis.dao.EmployeeMapperAnnotation;
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.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import static org.junit.Assert.*;

public class MyBatisTest {
    //获取SQLSessionFactory
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    /**
     * 测试删除
     */
    @Test
    public void test5() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        //获取到的sql不会自动提交数据
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try{
            EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
            Boolean isOK = mapper.deleteEmpById(3);
            //提交
            sqlSession.commit();
            if (isOK){
                System.out.println("删除成功");
            }else{
                System.out.println("删除失败");
            }
        }finally {
            sqlSession.close();
        }
    }
}

4.测试查询

package com.cerr.mybatis;
import com.cerr.mybatis.dao.EmployeeMapper;
import com.cerr.mybatis.dao.EmployeeMapperAnnotation;
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.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import static org.junit.Assert.*;

public class MyBatisTest {
    //获取SQLSessionFactory
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void test1() throws IOException {
        //获取SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        //获取SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try {
            //获取接口的实现类对象：会为接口自动的创建一个代理对象，代理对象去执行增删改查
            EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
            //调用方法
            Employee employee = employeeMapper.getEmpById(1);
            //打印
            System.out.println(employee);
        }finally {
            //关闭
            sqlSession.close();
        }
    }
}

insert获取自增主键的值

mysql支持自增主键的获取，而MyBatis也支持，利用statament.genGenreatedKeys()进行获取。需要在sql映射文件的<insert>中配置属性useGeneratekKeys的值为true，表示使用自增主键获取主键值策略。
还需要使用keyProperty属性来指定对应的主键属性，也就是mybatis获取到主键值以后，将这个值封装给javaBean的哪个属性。

<?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.cerr.mybatis.dao.EmployeeMapper">
    <!-- 增 -->
    <insert id="addEmp" parameterType="com.cerr.mybatis.Employee"
            useGeneratedKeys="true" keyProperty="id">
        insert into tb1_employee(last_name,email,gender) values(#{lastName},#{email},#{gender})
    </insert>
</mapper>

package com.cerr.mybatis;

import com.cerr.mybatis.dao.EmployeeMapper;
import com.cerr.mybatis.dao.EmployeeMapperAnnotation;
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.junit.Test;
import java.io.IOException;
import java.io.InputStream;
import static org.junit.Assert.*;

public class MyBatisTest {

    //获取SQLSessionFactory
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }
    /**
     * 测试添加
     */
    @Test
    public void test3() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        //获取到的sql不会自动提交数据
        SqlSession sqlSession = sqlSessionFactory.openSession();
        try{
            EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
            Employee employee = new Employee(null,"jerry","jerry@qq.com","1");
            Boolean isOk = mapper.addEmp(employee);
            //提交
            sqlSession.commit();
            System.out.println(isOk);
            System.out.println(employee.getId());
        }finally {
            sqlSession.close();
        }
    }
}

在添加方法中加上打印id的值，成功打印出来，之前实例化的employee对象的id值是空的，因此可以证明是获取自增主键的功能起了作用。


MyBatis的参数处理

可查看：MyBatis笔记 | 详解参数处理（多种类型的参数处理、源码分析、读取参数的两种格式的区别）

select元素

Select元素来定义查询操作

  • id：唯一标识符
    用来引用这条语句，需要和接口的方法名一致
  • parameterType：参数类型
    可以不传，MyBatis会根据TypeHandler自动推断
  • resultType：返回值类型
    别名或全类名，如果返回的是集合，定义集合中元素的类型。不能和resultMap同时使用。
  • resultMap：用来实现高级结果映射集，自定义封装规则等等

对于resultType和resultMap可以进入以下链接参考此文章：MyBatis笔记 | 详解resultType和resultMap

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