mybatis-关联关系2
关系关系主要有一对一，一对多，多对多，往往多对多都是通过俩个一对多来完成的
实例项目还是之前的，只是增加了一个年级实体类
1.创建年级实体类：---年级中有学生的集合
package com.java1234.model;
import java.util.List;
public class Grade {
private Integer id;
private String gradeName;
private List<Student> students;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getGradeName() {
return gradeName;
}
public void setGradeName(String gradeName) {
this.gradeName = gradeName;
}
public List<Student> getStudents() {
return students;
}
public void setStudents(List<Student> students) {
this.students = students;
}
@Override
public String toString() {
return "Grade [id=" + id + ", gradeName=" + gradeName +"]";
}
}
2创建年级dao
package com.java1234.mappers;
import com.java1234.model.Grade;
public interface GradeMapper {
public Grade findById(Integer id);
}
3.创建年级的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">
<mapper namespace="com.java1234.mappers.GradeMapper">
<resultMap type="Grade" id="GradeResult">
<result property="id" column="id"/>
<result property="gradeName" column="gradeName"/>
<collection property="students" column="id" select="com.java1234.mappers.StudentMapper.findByGradeId"></collection>
</resultMap>
<select id="findById" parameterType="Integer" resultMap="GradeResult">
select * from t_grade where id=#{id}
</select>
</mapper>
4.在学生实体类中添加年级对象
package com.java1234.model;
public class Student {
private Integer id;
private String name;
private Integer age;
private Address address;
private Grade grade;
public Student() {
super();
// TODO Auto-generated constructor stub
}
public Student(Integer id, String name, Integer age) {
super();
this.id = id;
this.name = name;
this.age = age;
}
public Student(String name, Integer age) {
super();
this.name = name;
this.age = age;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
public Grade getGrade() {
return grade;
}
public void setGrade(Grade grade) {
this.grade = grade;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", age=" + age
+ ", address=" + address + ", grade=" + grade + "]";
}
}
5.在学生dao中添加对根据年级查询学生
package com.java1234.mappers;
import java.util.List;
import com.java1234.model.Student;
public interface StudentMapper {
public int add(Student student);
public int update(Student student);
public int delete(Integer id);
public Student findById(Integer id);
public List<Student> find();
public Student findStudentWithAddress(Integer id);
public Student findByGradeId(Integer gradeId);
}
6在学生mapper中添加对年级的关联：
<?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.java1234.mappers.StudentMapper">
<!-- <resultMap type="Student" id="StudentResult">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="age" column="age"/>
<result property="address.id" column="addressId"/>
<result property="address.sheng" column="sheng"/>
<result property="address.shi" column="shi"/>
<result property="address.qu" column="qu"/>
</resultMap> -->
<!-- <resultMap type="Address" id="AddressResult">
<result property="id" column="id"/>
<result property="sheng" column="sheng"/>
<result property="shi" column="shi"/>
<result property="qu" column="qu"/>
</resultMap>
<resultMap type="Student" id="StudentResult">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="age" column="age"/>
<association property="address" resultMap="AddressResult"/>
</resultMap> -->
<resultMap type="Student" id="StudentResult">
<id property="id" column="id"/>
<result property="name" column="name"/>
<result property="age" column="age"/>
<association property="address" column="addressId" select="com.java1234.mappers.AddressMapper.findById"></association>
<association property="grade" column="gradeId" select="com.java1234.mappers.GradeMapper.findById"></association>
</resultMap>
<select id="findStudentWithAddress" resultMap="StudentResult" parameterType="Integer">
select * from t_student t1,t_address t2 where t1.addressId=t2.id and t1.id=#{id}
</select>
<select id="findByGradeId" resultMap="StudentResult" parameterType="Integer">
select * from t_student where gradeId=#{gradeId}
</select>
<insert id="add" parameterType="Student" >
insert into t_student values(null,#{name},#{age})
</insert>
<update id="update" parameterType="Student">
update t_student set name=#{name},age=#{age} where id=#{id}
</update>
<delete id="delete" parameterType="Integer">
delete from t_student where id=#{id}
</delete>
<select id="findById" parameterType="Integer" resultType="Student">
select * from t_student where id=#{id}
</select>
<select id="find" resultMap="StudentResult">
select * from t_student
</select>
</mapper>
7.建立测试：
package com.java1234.service;
import org.apache.ibatis.session.SqlSession;
import org.apache.log4j.Logger;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import com.java1234.mappers.StudentMapper;
import com.java1234.model.Student;
import com.java1234.util.SqlSessionFactoryUtil;
public class StudentTest3 {
private static Logger logger=Logger.getLogger(StudentTest.class);
private SqlSession sqlSession=null;
private StudentMapper studentMapper=null;
/**
* 测试方法前调用
* @throws Exception
*/
@Before
public void setUp() throws Exception {
sqlSession=SqlSessionFactoryUtil.openSession();
studentMapper=sqlSession.getMapper(StudentMapper.class);
}
/**
* 测试方法后调用
* @throws Exception
*/
@After
public void tearDown() throws Exception {
sqlSession.close();
}
@Test
public void testFindStudentWithAddress() {
logger.info("查询学生(带地址)");
Student student=studentMapper.findStudentWithAddress(3);
System.out.println(student);
}
@Test
public void testFindStudentWithGrade(){
logger.info("查询学生(带年级)");
Student student=studentMapper.findStudentWithAddress(1);
System.out.println(student);
}
}
