Mybatis基于注解方式表关系实现总结

清疚 2024-04-18 09:04 55阅读 0赞

前提：mybatis注解方式开发环境搭建完成。

### 一、一对一 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NobGVpXw_size_16_color_FFFFFF_t_70][]

![20190904143954833.png][]

![20190904144015392.png][]

SqlMapConfig.xml:

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE configuration
            PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-config.dtd">
    
    <configuration>
        
        <environments default="mysql">
            
            <environment id="mysql">
                
                <transactionManager type="JDBC"></transactionManager>
                
                <dataSource type="POOLED">
                    
                    <property name="driver" value="com.mysql.jdbc.Driver"/>
                    <property name="url" value="jdbc:mysql:///text2"/>
                    <property name="username" value="root"/>
                    <property name="password" value="123"/>
                </dataSource>
            </environment>
        </environments>
    
        
        <mappers>
            <mapper class="com.chenlei.dao.StudentDao"/>
            <mapper class="com.chenlei.dao.ScoresDao"/>
            <mapper class="com.chenlei.dao.TeacherDao"/>
        </mappers>
    </configuration>

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<Scores> 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<Student> 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> scores = scoresDao.findAll();
            for (Scores scorez : scores) {
                System.out.println("-------------");
                System.out.println(scorez);
                System.out.println(scorez.getStudent());
            }
        }
    }

结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NobGVpXw_size_16_color_FFFFFF_t_70 1][]

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）：

![20190904151123949.png][]

![20190904151150189.png][]

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> scores;
    
        public List<Scores> getScores() {
            return scores;
        }
    
        public void setScores(List<Scores> 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<Scores> 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<Student> 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<Student> students = studentDao.findAll();
            for (Student student : students) {
                System.out.println(student);
                System.out.println(student.getScores());
            }
        }
    }

结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NobGVpXw_size_16_color_FFFFFF_t_70 2][]

顺带提一下开启二级缓存的注解：

![20190904152444934.png][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NobGVpXw_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/0d1c3f4bc0ed4f6790765567af8aeabc.png
[20190904143954833.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/69d4d44ce9d14df7aad4135049ced4d0.png
[20190904144015392.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/ae1b8e72abf94a1cb6f77a7b5eaeacad.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NobGVpXw_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/4cafc67c0fd942ae810a380ba5ff048e.png
[20190904151123949.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/2563af0c3b574c9aaa77c1f26c3412c1.png
[20190904151150189.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/fc9caacbd7a64f5fa1d62b929dfc9bc0.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NobGVpXw_size_16_color_FFFFFF_t_70 2]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/913e1dda56e74b17872fdb36073c020c.png
[20190904152444934.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/940cfa32c57b4049b3d653efadbeb9c0.png