自动映射

  • 全局setting设置
    • autoMappingBehavior默认是PARTIAL，开启自动映射的功能，唯一的要求是列名和javaBean属性名一致
    • 如果autoMappingBehavior设置为null则会取消自动映射
    • 数据库字段命名规范，POJO属性符合驼峰命名法，如A_COLUMN—>aColumn，我们可以开启自动驼峰命名规则映射功能，mapUnderscoreToCamelCase=true
  • 自定义resultMap，实现高级结果集映射

第一个例子

定义接口

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public interface EmployeeMapperPlus {
	public Employee getEmpById(Integer id);
}

定义映射文件

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<?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.glemontree.mybatis.dao.EmployeeMapperPlus">
	<!-- <select id="getEmpById" resultType="com.glemontree.mybatis.bean.Employee">
		select * from tbl_employee where id = #{id}
	</select> -->
	
	<!-- resultMap：自定义结果集映射规则 -->
	<!-- 
		自定义javaBean的封装规则 
		type：自定义规则的Java类型
		id：唯一标识符，方便引用	
	-->
	<resultMap type="com.glemontree.mybatis.bean.Employee" id="MyEmp">
		<!-- 
			指定主键列的封装规则 
			id定义主键底层会有优化
			column：指定哪一列
			property：指定对应的JavaBean属性
		-->
		<id column="id" property="id"/>
		<!-- result定义普通列封装规则 -->
		<result column="last_name" property="lastName"/>
		<!-- 其他不指定的列会进行自动封装，推荐写上全部的映射规则 -->
		<result column="email" property="email"/>
		<result column="gender" property="gender"/>
	</resultMap>
	<select id="getEmpById" resultMap="MyEmp">
		select * from tbl_employee where id = #{id}
	</select>
</mapper>

测试

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@Test
public void test06() throws IOException {
    SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
    SqlSession openSession = sqlSessionFactory.openSession();
    try {
        EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
        Employee employee = mapper.getEmpById(1);
        System.out.println(employee);
    } finally {
      	openSession.close();
    }
}

第二个例子

Employee

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package com.glemontree.mybatis.bean;
import org.apache.ibatis.type.Alias;
public class Employee {
	private Integer id;
	private String lastName;
	private String email;
	private String gender;
	private Department dept;
	public Department getDept() {
		return dept;
	}
	public void setDept(Department dept) {
		this.dept = dept;
	}
	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) {
		super();
		this.id = id;
		this.lastName = lastName;
		this.email = email;
		this.gender = gender;
	}
	public Employee() {
	}
}

Department

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package com.glemontree.mybatis.bean;
public class Department {
	private Integer id;
	private String departmentName;
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getDepartmentName() {
		return departmentName;
	}
	public void setDepartmentName(String departmentName) {
		this.departmentName = departmentName;
	}
	@Override
	public String toString() {
		return "Department [id=" + id + ", departmentName=" + departmentName
				+ "]";
	}
}

接口

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public Employee getEmpAndDept(Integer id);

映射文件

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<!-- 联合查询：级联属性封装结果集 -->
<resultMap type="com.glemontree.mybatis.bean.Employee" id="MyDifEmp">
    <id column="id" property="id"/>
    <result column="last_name" property="lastName"/>
    <result column="gender" property="gender"/>
    <result column="did" property="dept.id"/>
    <result column="dept_name" property="dept.departmentName"/>
</resultMap>
<select id="getEmpAndDept" resultMap="MyDifEmp">
    SELECT e.id id, e.last_name last_name, e.gender gender, e.d_id d_id, d.id did, d.dept_name dept_name FROM tbl_employee e, tbl_dept d
    WHERE e.d_id = d.id
    AND e.id = #{id}
</select>

小结

上面这段程序展示了使用resultMap进行关联查询，在resultMap中使用级联属性封装结果集：

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<result column="did" property="dept.id"/>
<result column="dept_name" property="dept.departmentName"/>

其实还有另外一种方法可以用来定义关联的单个对象的封装规则：

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<!-- 使用association定义关联的单个对象的封装规则 -->
<resultMap type="com.glemontree.mybatis.bean.Employee" id="MyDifEmp2">
    <id column="id" property="id"/>
    <result column="last_name" property="lastName"/>
    <result column="gender" property="gender"/>
    <!-- 
     association可以指定联合的javaBean对象 
     property="dept"：指定哪个属性时联合的对象
     javaType：指定这个属性对象的类型[不能省略]
    -->
    <association property="dept" javaType="com.glemontree.mybatis.bean.Department">
        <id column="did" property="id"/>
        <result column="dept_name" property="departmentName"/>
    </association>
</resultMap>

推荐使用这种方法。