MyBatis 多对一关系

Employee类

public class Employee {

    private int id;
    private String name;
    private int age;
    private String sex;

    private Department department;



    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    public Employee() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Employee(String name, int age, String sex) {
        super();
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public Employee(int id, String name, int age, String sex) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "Employee [id=" + id + ", name=" + name + ", age=" + age
                + ", sex=" + sex + "]";
    }

}

EmployeeDao

public interface EmployeeDao {

    List<Employee> getEmployees() throws Exception;
    Employee getEmployeeById(int id) throws Exception;
}

EmployeeDao的映射文件

<?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.hsj.dao.EmployeeDao">

    <resultMap type="employee" id="resultMap_Employee">
        <id column="e_id" property="id"/>
        <result column="e_name" property="name"/>
        <result column="e_age" property="age"/>
        <result column="e_sex" property="sex"/>

        **<!-- 
        映射实体类中普通的POJO对象时使用的标签
        property="department":指定复杂属性的名字
        column="depart_id"：指定外键字段的名字
        javaType="department":复杂属性的数据类型
         -->**
        <**association** property="department" column="depart_id" javaType="department">
            <id column="d_id" property="id"/>
            <result column="d_name" property="name"/>
        </association>
    </resultMap>

    <!-- 查询所有雇员和部门信息 -->
    <select id="getEmployees" resultMap="resultMap_Employee">
        select * from t_employee e inner join t_department d on e.depart_id=d.d_id
    </select>


    <!-- 根据雇员编号好像雇员及其部门信息 -->
    <select id="getEmployeeById" parameterType="int" resultMap="resultMap_Employee">
        select * from t_employee e inner join t_department d on e.depart_id=d.d_id and e_id=#{id}
    </select>



</mapper>

Department类

public class Department {

    private int id;
    private String name;

    private Set<Employee> employees;

    public Set<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(Set<Employee> employees) {
        this.employees = employees;
    }

    public Department() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Department(int id, String name) {
        super();
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Department [id=" + id + ", name=" + name + "]";
    }

}

DepartmentDao

public interface DepartmentDao {

    List<Department> getDepartments() throws Exception;


    Department getDepartmentById(int id) throws Exception;
}

DepartmentDao的映射文件

<?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.hsj.dao.DepartmentDao">

    <resultMap type="department" id="resultMap_Department">
        <id column="d_id" property="id"/>
        <result column="d_name" property="name"/>

        **<!-- 
        如果映射的复杂属性是集合，则可以使用collection标签来映射
        property="employees":复杂属性的名字 
        column="depart_id"：指定外键字段的名字
        ofType="employee"：指定集合中元素的数据类型
         -->**
        <collection property="employees" column="depart_id" ofType="employee">
            <id column="e_id" property="id"/>
            <result column="e_name" property="name"/>
            <result column="e_age" property="age"/>
            <result column="e_sex" property="sex"/>
        </collection>
    </resultMap>


    <select id="getDepartments" resultMap="resultMap_Department">
        select * from t_department d inner join t_employee e on d.d_id=e.depart_id
    </select>

    <select id="getDepartmentById" resultMap="resultMap_Department">
        select * from t_department d inner join t_employee e on d.d_id=e.depart_id and d_id=#{id}
    </select>

</mapper>

其中一个测试类

public class DepartmentDaoTest {

    private DepartmentDao departmentDao;

    @Before
    public void setUp() throws Exception {
        SqlSession sqlSession=MyBatisUtils.getSqlSession();

        this.departmentDao=sqlSession.getMapper(DepartmentDao.class);

    }

    @Test
    public void testGetDepartments() {
        try {
            List<Department> departments=this.departmentDao.getDepartments();
            for(Department department:departments){
                System.out.println(department);
                System.out.println("雇员信息：");

                for(Employee e :department.getEmployees()){
                    System.out.println(e);
                }

                System.out.println("============");
            }
            System.out.println();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Test
    public void testGetDepartmentById() {
        int id=1;
        try {
            Department department=this.departmentDao.getDepartmentById(id);
            System.out.println(department);
            System.out.println("雇员信息：");
            for(Employee e:department.getEmployees()){
                System.out.println(e);
            }


        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}