Mybatis——resultMap的使用方法

Employee

public class Employee {    private Integer id;    private String last_name;    private String email;    private String gender;    private Department department;    public Department getDepartment() {        return department;    }    public void setDepartment(Department department) {        this.department = department;    }    public Employee(Integer id, String last_name, String email, String gender) {        super();        this.id = id;        this.last_name = last_name;        this.email = email;        this.gender = gender;    }    public Employee(){    }    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getLast_name() {        return last_name;    }    public void setLast_name(String last_name) {        this.last_name = last_name;    }    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 + ", last_name=" + last_name + ", email=" + email + ", gender=" + gender + "]";    }}

Department

public class Employee {    private Integer id;    private String last_name;    private String email;    private String gender;    private Department department;    public Department getDepartment() {        return department;    }    public void setDepartment(Department department) {        this.department = department;    }    public Employee(Integer id, String last_name, String email, String gender) {        super();        this.id = id;        this.last_name = last_name;        this.email = email;        this.gender = gender;    }    public Employee(){    }    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getLast_name() {        return last_name;    }    public void setLast_name(String last_name) {        this.last_name = last_name;    }    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 + ", last_name=" + last_name + ", email=" + email + ", gender=" + gender + "]";    }}

接口 EmployeeMapperPlus.java

public interface EmployeeMapperPlus {    public Employee getEmpById(Integer id);    public Employee getEmpAndDept(Integer id);    public Employee getEmpByIdStep(Integer id);    public List<Employee> getEmpsByDeptId(Integer deptId);}

接口DepartmentMapper.java

public interface DepartmentMapper {    public Department getDeptById(Integer id);    public Department getDeptByIdPlus(Integer id);    public Department getDeptByIdStep(Integer id);}

EmployeeMapperPlus.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.mybatis.dao.EmployeeMapperPlus">    <!--自定义某个javaBean的封装规则    type：自定义规则的Java类型    id:唯一id方便引用      -->    <resultMap type="com.mybatis.bean.Employee" id="MySimpleEmp">        <!--指定主键列的封装规则        id定义主键会底层有优化；        column：指定哪一列        property：指定对应的javaBean属性          -->        <id column="id" property="id"/>        <!-- 定义普通列封装规则 -->        <result column="last_name" property="last_name"/>        <!-- 其他不指定的列会自动封装：我们只要写resultMap就把全部的映射规则都写上。 -->        <result column="email" property="email"/>        <result column="gender" property="gender"/>    </resultMap>        <!-- public Employee getEmpById(Integer id); -->        <!-- resultMap:自定义结果集映射规则；  -->        <select id="getEmpById" resultMap="MySimpleEmp">            select * from tbl_employee where id = #{id}        </select>        <!--     场景一：        查询Employee的同时查询员工对应的部门        Employee===Department        一个员工有与之对应的部门信息；        id  last_name  gender    d_id     did  dept_name (private Department dept;)     --><!--        联合查询：级联属性封装结果集      -->     <resultMap type="com.mybatis.bean.Employee" id="MyDifEmp">        <id column="id" property="id"/>        <result column="last_name" property="last_name"/>        <result column="gender" property="gender"/>        <result column="did" property="department.id"/>        <result column="dept_name" property="department.departmentName"/>    </resultMap>    <!--         使用association定义关联的单个对象的封装规则；     -->    <resultMap type="com.mybatis.bean.Employee" id="MyDifEmp2">        <id column="id" property="id"/>        <result column="last_name" property="last_name"/>        <result column="gender" property="gender"/>        <!--  association可以指定联合的javaBean对象        property="dept"：指定哪个属性是联合的对象        javaType:指定这个属性对象的类型[不能省略]        -->        <association property="department" javaType="com.mybatis.bean.Department">            <id column="did" property="id"/>            <result column="dept_name" property="departmentName"/>        </association>    </resultMap> <!--public Employee getEmpAndDept(Integer id); -->     <select id="getEmpAndDept" resultMap="MyDifEmp2">        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>     <!-- 使用association进行分步查询：        1、先按照员工id查询员工信息        2、根据查询员工信息中的d_id值去部门表查出部门信息        3、部门设置到员工中；     -->      <!--  id  last_name  email   gender    d_id   -->     <resultMap type="com.mybatis.bean.Employee" id="MyEmpByStep">        <id column="id" property="id"/>        <result column="last_name" property="last_name"/>        <result column="email" property="email"/>        <result column="gender" property="gender"/>        <!-- association定义关联对象的封装规则            select:表明当前属性是调用select指定的方法查出的结果            column:指定将哪一列的值传给这个方法            流程：使用select指定的方法（传入column指定的这列参数的值）查出对象，并封装给property指定的属性         -->        <association property="department"             select="com.mybatis.dao.DepartmentMapper.getDeptById"            column="d_id">        </association>     </resultMap>     <!--  public Employee getEmpByIdStep(Integer id);-->     <select id="getEmpByIdStep" resultMap="MyEmpByStep">        select * from tbl_employee where id=#{id}     </select>      <!-- 可以使用延迟加载（懒加载）；(按需加载)        Employee==>Dept：            我们每次查询Employee对象的时候，都将一起查询出来。            部门信息在我们使用的时候再去查询；            分段查询的基础之上加上两个配置：      -->      <!--     场景二：        查询部门的时候将部门对应的所有员工信息也查询出来：注释在DepartmentMapper.xml中     -->     <!-- public List<Employee> getEmpsByDeptId(Integer deptId); -->    <select id="getEmpsByDeptId" resultType="com.mybatis.bean.Employee">        select * from tbl_employee where d_id=#{deptId}    </select>    <!-- =======================鉴别器============================ -->    <!-- <discriminator javaType=""></discriminator>        鉴别器：mybatis可以使用discriminator判断某列的值，然后根据某列的值改变封装行为        封装Employee：            如果查出的是女生：就把部门信息查询出来，否则不查询；            如果是男生，把last_name这一列的值赋值给email;     -->     <resultMap type="com.mybatis.bean.Employee" id="MyEmpDis">        <id column="id" property="id"/>        <result column="last_name" property="last_name"/>        <result column="email" property="email"/>        <result column="gender" property="gender"/>        <!--            column：指定判定的列名            javaType：列值对应的java类型  -->        <discriminator javaType="string" column="gender">            <!--女生  resultType:指定封装的结果类型；不能缺少。/resultMap-->            <case value="0" resultType="com.mybatis.bean.Employee">                <association property="dept"                     select="com.mybatis.dao.DepartmentMapper.getDeptById"                    column="d_id">                </association>            </case>            <!--男生 ;如果是男生，把last_name这一列的值赋值给email; -->            <case value="1" resultType="com.mybatis.bean.Employee">                <id column="id" property="id"/>                <result column="last_name" property="last_name"/>                <result column="last_name" property="email"/>                <result column="gender" property="gender"/>            </case>        </discriminator>     </resultMap> </mapper>

DepartmentMapper.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.mybatis.dao.DepartmentMapper">    <!-- public Department getDeptById(Integer id); -->    <select id="getDeptById" resultType="com.mybatis.bean.Department">        select id,dept_name departmentName from tbl_dept where id=#{id}    </select>    <!--嵌套结果集的方式，使用collection标签定义关联的集合类型的属性封装规则  -->    <resultMap type="com.mybatis.bean.Department" id="MyDept">        <id column="did" property="id"/>        <result column="dept_name" property="departmentName"/>        <!--             collection定义关联集合类型的属性的封装规则             ofType:指定集合里面元素的类型        -->        <collection property="emps" ofType="com.mybatis.bean.Employee">            <!-- 定义这个集合中元素的封装规则 -->            <id column="eid" property="id"/>            <result column="last_name" property="last_name"/>            <result column="email" property="email"/>            <result column="gender" property="gender"/>        </collection>    </resultMap>    <!--    public Department getDeptByIdPlus(Integer id); -->    <select id="getDeptByIdPlus" resultMap="MyDept">        SELECT d.id did,d.dept_name dept_name,                e.id eid,e.last_name last_name,e.email email,e.gender gender        FROM tbl_dept d        LEFT JOIN tbl_employee e        ON d.id=e.d_id        WHERE d.id=#{id}    </select>    <!-- collection：分段查询 -->    <resultMap type="com.mybatis.bean.Department" id="MyDeptStep">        <id column="id" property="id"/>        <result column="dept_name" property="departmentName"/>        <collection property="emps"             select="com.mybatis.dao.EmployeeMapperPlus.getEmpsByDeptId"            column="{deptId=id}"></collection>    </resultMap>    <!-- public Department getDeptByIdStep(Integer id); -->    <select id="getDeptByIdStep" resultMap="MyDeptStep">        select id,dept_name from tbl_dept where id=#{id}    </select>    <!-- 扩展：多列的值传递过去：            将多列的值封装map传递；            column="{key1=column1,key2=column2}"        fetchType="lazy"：表示使用延迟加载；                - lazy：延迟                - eager：立即     --> </mapper>

Test

@Test    public void test07() throws IOException{        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();        SqlSession openSession = sqlSessionFactory.openSession();        try {            EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);        /*  Employee employee = mapper.getEmpById(1);*/            /*Employee empAndDept = mapper.getEmpAndDept(3);            System.out.println(empAndDept);            System.out.println(empAndDept.getDepartment());*/            //分布查询            Employee employee = mapper.getEmpByIdStep(3);            System.out.println(employee.getLast_name());            /*System.out.println(employee.getDepartment());*/        } finally {            openSession.close();        }    }    @Test    public void test08() throws IOException{        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();        SqlSession openSession = sqlSessionFactory.openSession();        try {            DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.class);            /*Department department = mapper.getDeptByIdPlus(1);            System.out.println(department);            System.out.println(department.getEmps());*/            //分布查询            Department department = mapper.getDeptByIdStep(2);            System.out.println(department);            System.out.println(department.getEmps());        } finally {            openSession.close();        }    }