一、many2one（保存时，关系交给many方来进行处理）
1.实体类（实体类属性满足驼峰匹配的话，如userName,resultMap中添加autoMapping='true',则里面只需要写id映射，其余的挥动匹配映射）
public class Department {
private Long id;
private String name;
}
public class Employee {
private long id ;
private String name;
private Department dept;// 数据库中外键为dept_id
}2.Dao接口类
public interface IDepartmentMapper {
void save(Department department);
Department get(Long id);
}
public interface IEmployeeMapper {
void save(Employee employee);
Employee get(Long id);
List<Employee> getList();
}3.XML（DepartmentMapper.xml和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:名称空间，全局的唯一标识 -->
<mapper namespace="com.shenzhenair.mybatis.demo_02.many2one.IDepartmentMapper">
<insert id="save" parameterType="Department" keyColumn="id" keyProperty="id" useGeneratedKeys="true" >
INSERT INTO department (name) VALUES (#{name})
</insert>
<select id="get" parameterType="java.lang.Long" resultType="Department">
SELECT id,name from department where id = #{id}
</select>
</mapper>1.在查询所有many记录,每个many对应的one都是不同,查询N个many对象,总共会发出N+1条SQL.(性能特别不友好) 使用leftJoin的方式来解决.
<?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:名称空间，全局的唯一标识 -->
<mapper namespace="com.shenzhenair.mybatis.demo_02.many2one.IEmployeeMapper" >
<resultMap id="base_employeeMap" type="Employee" autoMapping="true" >
<id column="id" property="id" ></id>
<result column="name" property="name" ></result>
<!--
association关联关系：
property:表示实体类中关联关系的属性名
javaType:查询出来实体类中的类型
select:表示需要发送sql去查询出关联对象的sql映射
column:查询出来的哪个字段作为作为参数调用select中的SQL，此处dept_id作为映射get中的参数
columnPrefix:给映射的column添加前缀信息 dept_id,dept_name
此种关联会发送额外的sql
<association column="dept_id" property="dept" javaType="Department" select="com.shenzhenair.mybatis.demo_02.many2one.IDepartmentMapper.get" ></association>
-->
<association property="dept" javaType="Department" columnPrefix="dept_" autoMapping="true" >
<id column="id" property="id"></id>
<result column="name" property="name"></result>
</association>
</resultMap>
<insert id="save" parameterType="Employee" keyColumn="id" keyProperty="id" useGeneratedKeys="true" >
INSERT INTO employee (name,dept_id) VALUES (#{name},#{dept.id})
</insert>
<select id="get" parameterType="java.lang.Long" resultMap="base_employeeMap">
SELECT id,name,dept_id from employee where id = #{id}
</select>
<select id="getList" resultMap="base_employeeMap">
/* SELECT id,name,dept_id from employee*/
SELECT e.id,e.name,d.id AS dept_id,d.name AS dept_name FROM employee e LEFT JOIN
department d ON e.dept_id = d.id
</select>
</mapper>4.测试类
public class TestMany2One {
@Test
public void testSave(){
SqlSession session = MybatisUtils.openSession();
IDepartmentMapper deptMapper = session.getMapper(IDepartmentMapper.class);
IEmployeeMapper empMapper = session.getMapper(IEmployeeMapper.class);
Department department = new Department("IT部门");
Employee employee = new Employee("tom");
employee.setDept(department);
// 先保存one方，再保存many方
deptMapper.save(department);
empMapper.save(employee);
session.commit();
session.close();
}
@Test
public void testGetEmployee(){
SqlSession session = MybatisUtils.openSession();
IEmployeeMapper empMapper = session.getMapper(IEmployeeMapper.class);
Employee employee = empMapper.get(1l);
Department dept = employee.getDept();
System.out.println(employee);
System.out.println(dept);
session.commit();
session.close();
}
@Test
public void testGetEmployeeList(){
SqlSession session = MybatisUtils.openSession();
IEmployeeMapper empMapper = session.getMapper(IEmployeeMapper.class);
List<Employee> employee = empMapper.getList();
for (Employee employee1 : employee) {
System.out.println(employee1);
}
session.commit();
session.close();
}
@Test
public void testGetDepartment(){
SqlSession session = MybatisUtils.openSession();
IDepartmentMapper deptMapper = session.getMapper(IDepartmentMapper.class);
Department department = deptMapper.get(2L);
System.out.println(department);
session.commit();
session.close();
}
}
2.One2Many（one方要处理外键关系）
1.实体类
public class Department {
private Long id;
private String name;
private List<Employee> employees = new ArrayList<>();
}
public class Employee {
private long id ;
private String name;
}2.Dao接口
public interface IDepartmentMapper {
void save(Department department);
Department get(Long id);
void handlerRelaotion(@Param("dept_id") Long deptID, @Param("emp_id") long empID);
void delete(Long id);
}
public interface IEmployeeMapper {
void save(Employee employee);
Employee get(Long id);
Employee selectByDeptID(Long dept_id);
void updateRelation(Long id);
}3.XML(DepartmentMapper.xml, 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:名称空间，全局的唯一标识 -->
<mapper namespace="com.shenzhenair.mybatis.demo_02.one2many.IDepartmentMapper">
<resultMap id="basic_map" type="Department">
<id column="id" property="id" ></id>
<result column="name" property="name" ></result>
<!--
ofType:查询出来的集合中的类型
<collection column="id" property="employees" ofType="Employee" select="com.shenzhenair.mybatis.demo_02.one2many.ITeacherMapper.selectByDeptID" />
-->
<collection property="employees" ofType="Employee" columnPrefix="emp_" >
<id column="id" property="id" ></id>
<result column="name" property="name"></result>
</collection>
</resultMap>
<!-- <select id="get" parameterType="java.lang.Long" resultMap="basic_map">
SELECT id,name from department where id = #{id}
</select>-->
<select id="get" parameterType="java.lang.Long" resultMap="basic_map">
SELECT d.id as id,d.name as name ,e.id as emp_id,e.name as emp_name from department d LEFT JOIN employee e on d.id=e.dept_id WHERE d.id = #{id}
</select>
<insert id="save" parameterType="Department" keyColumn="id" keyProperty="id" useGeneratedKeys="true" >
INSERT INTO department (name) VALUES (#{name})
</insert>
<update id="handlerRelaotion" parameterType="java.lang.Long" >
UPDATE employee set dept_id=#{dept_id} WHERE id = #{emp_id}
</update>
<delete id="delete">
DELETE FROM department where id=#{id}
</delete>
</mapper><?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:名称空间，全局的唯一标识 -->
<mapper namespace="com.shenzhenair.mybatis.demo_02.one2many.IEmployeeMapper" >
<insert id="save" parameterType="Employee" keyColumn="id" keyProperty="id" useGeneratedKeys="true" >
INSERT INTO employee (name) VALUES (#{name})
</insert>
<select id="get" parameterType="java.lang.Long" resultType="Employee">
SELECT id,name from employee where id = #{id}
</select>
<select id="selectByDeptID" parameterType="java.lang.Long" resultType="Employee">
SELECT id,name from employee where dept_id = #{dept_id}
</select>
<update id="updateRelation" parameterType="long" >
update employee set dept_id = null where dept_id=#{id}
</update>
</mapper>4.测试类
public class TestOne2Many {
@Test
public void testSave(){
SqlSession session = MybatisUtils.openSession();
IDepartmentMapper deptMapper = session.getMapper(IDepartmentMapper.class);
IEmployeeMapper empMapper = session.getMapper(IEmployeeMapper.class);
Employee employee1 = new Employee("e1");
Employee employee2 = new Employee("e2");
Department department = new Department("dept1");
department.getEmployees().add(employee1);
department.getEmployees().add(employee2);
deptMapper.save(department);
empMapper.save(employee1);
empMapper.save(employee2);
// 需要one方处理外键的关系
List<Employee> employees = department.getEmployees();
for (Employee employee : employees) {
deptMapper.handlerRelaotion(department.getId(),employee.getId());
}
session.commit();
session.close();
}
@Test
public void testGet(){
SqlSession session = MybatisUtils.openSession();
IDepartmentMapper deptMapper = session.getMapper(IDepartmentMapper.class);
Department department = deptMapper.get(6L);
System.out.println(department);
List<Employee> employees = department.getEmployees();
for (Employee employee : employees) {
System.out.println(employee);
}
session.commit();
session.close();
}
@Test
public void testDeleteEmployee(){
SqlSession session = MybatisUtils.openSession();
IDepartmentMapper departmentMapper = session.getMapper(IDepartmentMapper.class);
IEmployeeMapper employeeMapper = session.getMapper(IEmployeeMapper.class);
// 打破外键约束关系
Department dept = departmentMapper.get(6L);
/*List<Employee> employees = dept.getEmployees();
for (Employee employee : employees) {
employeeMapper.updateRelation(employee.getId());
}*/
employeeMapper.updateRelation(dept.getId());
departmentMapper.delete(6L);
session.commit();
session.close();
}
}3.Many2Many
1. 实体类：
public class Student {
private Long id;
private String name;
}
public class Teacher {
private Long id;
private String name;
private List<Student> stus = new ArrayList<>();
}2.Dao接口
public interface IStudentMapper {
void save(Student student);
Student get(Long id);
}
public interface ITeacherMapper {
void save(Teacher teacher);
Teacher getTeacher(Long id);
Long handlerRelation (@Param("teaId") Long teaId, @Param("stuId") Long stuId);
}3.XML(StudentMapper.xml TeacherMapper.xml)
<mapper namespace="com.shenzhenair.mybatis.demo_02.many2many.IStudentMapper">
<select id="get" parameterType="java.lang.Long" resultType="Student">
select id,name from student where id = #{id}
</select>
<insert id="save" parameterType="Student" keyColumn="id" keyProperty="id" useGeneratedKeys="true" >
INSERT INTO student (name) VALUES (#{name})
</insert>
</mapper><mapper namespace="com.shenzhenair.mybatis.demo_02.many2many.ITeacherMapper" >
<insert id="save" parameterType="Teacher" keyColumn="id" keyProperty="id" useGeneratedKeys="true" >
INSERT INTO teacher (name) VALUES (#{name})
</insert>
<resultMap id="basic_map" type="Teacher">
<id column="id" property="id"></id>
<result column="name" property="name" ></result>
<!--是用内联方式进行查询-->
<collection property="stus" ofType="Student" columnPrefix="stu_">
<id property="id" column="id" ></id>
<result property="name" column="name"></result>
</collection>
</resultMap>
<select id="getTeacher" parameterType="java.lang.Long" resultMap="basic_map">
SELECT t.id as id,t.NAME as name,s.id AS stu_id,s.NAME AS stu_name FROM teacher t
LEFT JOIN tea_stu ts ON t.id = ts.t_id LEFT JOIN student s ON ts.s_id = s.id
WHERE t.id =#{id}
</select>
<!--处理中间表关系 -->
<insert id="handlerRelation">
INSERT INTO tea_stu (s_id,t_id) VAsLUES (#{stuId},#{teaId})
</insert>
</mapper>4.测试类
public class TestMany2Many {
@Test
public void testSave(){
SqlSession session = MybatisUtils.openSession();
IStudentMapper stuMapper = session.getMapper(IStudentMapper.class);
ITeacherMapper teaMapper = session.getMapper(ITeacherMapper.class);
Teacher t1 = new Teacher();
t1.setName("t1");
Teacher t2 = new Teacher();
t2.setName("t2");
Student stu1 = new Student();
stu1.setName("s1");
Student stu2 = new Student();
stu2.setName("s2");
t1.getStus().add(stu1);
t1.getStus().add(stu2);
t2.getStus().add(stu1);
t2.getStus().add(stu2);
teaMapper.save(t1);
teaMapper.save(t2);
stuMapper.save(stu1);
stuMapper.save(stu2);
// 需要处理中间表的关系
List<Student> stus1 = t1.getStus();
for (Student student : stus1) {
teaMapper.handlerRelation(t1.getId(),student.getId());
}
List<Student> stus2 = t1.getStus();
for (Student student : stus2) {
teaMapper.handlerRelation(t2.getId(),student.getId());
}
session.commit();
session.close();
}
@Test
public void testGet(){
SqlSession session = MybatisUtils.openSession();
ITeacherMapper teaMapper = session.getMapper(ITeacherMapper.class);
Teacher teacher = teaMapper.getTeacher(2L);
System.out.println(teacher);
List<Student> stus = teacher.getStus();
for (Student student : stus) {
System.out.println(student);
}
session.commit();
session.close();
}