MyBatis中当实体类中的属性名和表中的字段名不一样怎么办 ？

解决方案：
1.写sql语句时起别名
2.在MyBatis的全局配置文件中开启驼峰命名规则
3.在Mapper映射文件中使用resultMap来自定义映射规则

代码show

• 代码结构图

• 核心jar包：

• 核心代码
  • 配置
    • EmployeeMapper.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">
<!-- namespace属性：必须是接口的全类名 -->
<mapper namespace="cn.wangzengqiang.interview.atguigu2019.javaee.mybatis.mapper.EmployeeMapper">
	<!-- 
		id属性：必须是接口中方法的方法名
		resultType属性：必须是方法的返回值的全类名
	 -->
	<!-- 属性取不到值 -->
	<!--<select id="getEmployeeById" resultType="cn.wangzengqiang.interview.atguigu2019.javaee.mybatis.entities.Employee">
		select * from employees where id = #{id}
	</select>-->
	<!--解决方案1：sql起别名-->
	<!--<select id="getEmployeeById" resultType="cn.wangzengqiang.interview.atguigu2019.javaee.mybatis.entities.Employee">
		select id,last_name lastName,email,salary,dept_id deptId from employees where id = #{id}
	</select>-->

	<!--解决方案2：开启驼峰命名配置 mybatis-config.xml配置-->
	<!--<select id="getEmployeeById" resultType="cn.wangzengqiang.interview.atguigu2019.javaee.mybatis.entities.Employee">
		select * from employees where id = #{id}
	</select>-->

	<!--解决方案3：自定义映射-->
	<select id="getEmployeeById" resultMap="myMap">
		select * from employees where id = #{id}
	</select>
	
	<!-- 自定义高级映射 -->
    <resultMap type="cn.wangzengqiang.interview.atguigu2019.javaee.mybatis.entities.Employee" id="myMap">
    	<!-- 映射主键 -->
    	<id column="id" property="id"/>
    	<!-- 映射其他列 -->
    	<result column="last_name" property="lastName"/>
    	<result column="email" property="email"/>
    	<result column="salary" property="salary"/>
    	<result column="dept_id" property="deptId"/>
    </resultMap>
</mapper>

• 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>

- 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>
<!-- 	<settings>-->
		 <!-- 开启驼峰命名规则 ，可以将数据库中的下划线映射为驼峰命名
		 	例如：last_name可以映射为lastName
		 -->
<!-- 		<setting name="mapUnderscoreToCamelCase" value="true"/>-->
<!-- 	</settings>-->
	<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/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="123456" />
			</dataSource>
		</environment>
	</environments>
	<!-- 注册映射文件 -->
	<mappers>
		<mapper resource="EmployeeMapper.xml" />
	</mappers>
</configuration>

• 核心类
  • Employee.java

public class Employee {

	private Integer id;
	private String lastName;
	private String email;
	private double salary;
	private Integer deptId;

	public Employee(Integer id, String lastName, String email, double salary, Integer deptId) {
		super();
		this.id = id;
		this.lastName = lastName;
		this.email = email;
		this.salary = salary;
		this.deptId = deptId;
	}

	public Employee() {
		super();
	}

	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 double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public Integer getDeptId() {
		return deptId;
	}

	public void setDeptId(Integer deptId) {
		this.deptId = deptId;
	}

	@Override
	public String toString() {
		return "Employee [id=" + id + ", lastName=" + lastName + ", email=" + email + ", salary=" + salary + ", deptId="
				+ deptId + "]";
	}

}

- EmployeeMapper.java

public interface EmployeeMapper {

	Employee getEmployeeById(Integer id);
}

- MyBatisTest.java

      public class MyBatisTest {
  
      //1.MyBatis中当实体类中的属性名和表中的字段名不一样 ，怎么办 ？
      /*
       * 解决方案：
       * 	1.写sql语句时起别名
       * 	2.在MyBatis的全局配置文件中开启驼峰命名规则
       *  3.在Mapper映射文件中使用resultMap来自定义映射规则
       */
  
      @Test
      public void testGetEmployee() throws IOException {
          //1.创建SqlSessionFactory对象
          String resource = "mybatis-config.xml";
          InputStream inputStream = Resources.getResourceAsStream(resource);
          SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
          //2.获取sqlSession，sqlSession就相当于JDBC中的connection
          SqlSession sqlSession = sqlSessionFactory.openSession();
          try {
              //3.获取Mapper对象
              EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
              //4.调用EmployeeMapper中获取Employee的方法
              Employee employee = mapper.getEmployeeById(1);
              System.out.println(employee);
          } finally {
              //5.关闭sqlSession
              sqlSession.close();
          }
      }
  
  }