Mybatis基于注解方式表关系实现总结
前提：mybatis注解方式开发环境搭建完成。
一、一对一
目录：
SqlMapConfig.xml:
实体类：
public class Student implements Serializable {
private Integer id;
private String name;
private String sex;
private Date birthday;
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 String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
", birthday=" + birthday +
'}';
}
}public class Scores implements Serializable {
private Integer id;
private Integer score;
private Integer sid;
//从表实体类应该包含一个主表实体类的对象引用
private Student student;
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getScore() {
return score;
}
public void setScore(Integer score) {
this.score = score;
}
public Integer getSid() {
return sid;
}
public void setSid(Integer sid) {
this.sid = sid;
}
@Override
public String toString() {
return "Scores{" +
"id=" + id +
", score=" + score +
", sid=" + sid +
'}';
}
}接口：
public interface ScoresDao {
/**
* 查询所有分数
* @return
*/
@Results(id = "scoresMap",value = {
@Result(id = true,column = "id",property = "id"),
@Result(column = "sid",property = "sid"),
@Result(column = "score",property = "score"),
@Result(column = "sid",property = "student",one = @One(select = "com.chenlei.dao.StudentDao.findById",fetchType = FetchType.EAGER))
})
@Select("select * from scores")
List findAll();
} public interface StudentDao {
/**
* 查找所有操作
* @return
*/
@Results(id = "studentMap",value = {
@Result(id = true,column = "id",property = "id"),
@Result(column = "name",property = "name"),
@Result(column = "sex",property = "sex"),
@Result(column = "birthday",property = "birthday")
})
@Select("select * from student")
List findAll();
/**
* 根据id查询学生
* @param id
*/
@Select("select * from student where id =#{id}")
@ResultMap("studentMap")
Student findById (Integer id);
} 测试类：
public class ScoresTest {
private InputStream in;
private SqlSession sqlSession;
private ScoresDao scoresDao;
//用于测试方法测试之前执行
@Before
public void init() throws IOException {
//1.读取配置文件
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//2.创建SqlSessionFactory工厂
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
//3.使用工厂生产SqlSession对象
sqlSession = factory.openSession();
///4.使用SqlSession创建Dao接口的代理对象
scoresDao = sqlSession.getMapper(ScoresDao.class);
}
//用于测试方法之后执行
@After
public void destroy() throws IOException {
//提交事务
sqlSession.commit();
//6.释放资源
sqlSession.close();
in.close();
}
@Test
public void findAll() {
//执行查询所有对象方法
List scores = scoresDao.findAll();
for (Scores scorez : scores) {
System.out.println("-------------");
System.out.println(scorez);
System.out.println(scorez.getStudent());
}
}
} 结果：
注意问题：
对于ScoresDao接口注释中one = @One中select属性是相当于是给我们一个对应的编号进行查询学生对象，从而获取这个对应的对象值，故select属性中所填的值是根据id查询学生对象的接口路径。
二、一对多
表格（一个学生有多个成绩）：
实体类改动：
public class Student implements Serializable {
private Integer id;
private String name;
private String sex;
private Date birthday;
//一对多的关系映射：主表实体应该包含从表实体的集合引用
private List scores;
public List getScores() {
return scores;
}
public void setScores(List scores) {
this.scores = scores;
}
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 String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
", birthday=" + birthday +
'}';
}
} public class Scores implements Serializable {
private Integer id;
private Integer score;
private Integer sid;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public Integer getScore() {
return score;
}
public void setScore(Integer score) {
this.score = score;
}
public Integer getSid() {
return sid;
}
public void setSid(Integer sid) {
this.sid = sid;
}
@Override
public String toString() {
return "Scores{" +
"id=" + id +
", score=" + score +
", sid=" + sid +
'}';
}
}接口：
public interface ScoresDao {
/**
* 根据学生信息查询成绩
* @param sid
* @return
*/
@Select("select * from scores where sid=#{#sid}")
List findScoresByid(Integer sid);
} public interface StudentDao {
/**
* 查找所有操作
* @return
*/
@Results(id = "studentMap",value = {
@Result(id = true,column = "id",property = "id"),
@Result(column = "name",property = "name"),
@Result(column = "sex",property = "sex"),
@Result(column = "birthday",property = "birthday"),
@Result(property = "scores",column = "id",many = @Many(
select = "com.chenlei.dao.ScoresDao.findScoresByid",
fetchType = FetchType.EAGER
))
})
@Select("select * from student")
List findAll();
} 测试类：
public class MybatisTest {
private InputStream in;
private SqlSession sqlSession;
private StudentDao studentDao;
//用于测试方法测试之前执行
@Before
public void init() throws IOException {
//1.读取配置文件
in = Resources.getResourceAsStream("SqlMapConfig.xml");
//2.创建SqlSessionFactory工厂
SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
//3.使用工厂生产SqlSession对象
sqlSession = factory.openSession();
///4.使用SqlSession创建Dao接口的代理对象
studentDao = sqlSession.getMapper(StudentDao.class);
}
//用于测试方法之后执行
@After
public void destroy() throws IOException {
//提交事务
sqlSession.commit();
//6.释放资源
sqlSession.close();
in.close();
}
@Test
public void findAll() {
//执行查询所有对象方法
List students = studentDao.findAll();
for (Student student : students) {
System.out.println(student);
System.out.println(student.getScores());
}
}
} 结果：
顺带提一下开启二级缓存的注解：
