Mybatis-注解多表操作-易微帮

目录

一对一的环境准备

一对一的功能实现

实例演示

一对多的环境准备

一对多的功能实现

实例演示

多对多的环境准备

多对多的功能实现

实例演示
一对一的环境准备
(数据表参考之前映射配置版多表操作)

public class Person {
    private Integer id; //主键id
    private String name;//人的姓名
    private Integer age;//人的年龄

    public Person() {
    }

    public Person(Integer id, String name, Integer age) {
        this.id = id;
        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;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class Card {
    private Integer id; //主键id
    private String number; //身份证号
    private Person p;//所属人的对象

    public Card() {
    }

    public Card(Integer id, String number, Person p) {
        this.id = id;
        this.number = number;
        this.p = p;
    }

    public Integer getId() {
        return id;
    }

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

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Person getP() {
        return p;
    }

    public void setP(Person p) {
        this.p = p;
    }

    @Override
    public String toString() {
        return "Card{" +
                "id=" + id +
                ", number='" + number + '\'' +
                ", p=" + p +
                '}';
    }
}

一对一的功能实现
@Results：封装映射关系的父注解
里面有Result[] value()：定义了Result数组
@Result：封装映射关系的子注解
column属性：查询出的表中字段名称
property属性：实体对象中的属性名称
javaType属性：被包含对象的数据类型
one属性：一对一查询固定属性
@One：一对一查询的注解
select属性：指定调用某个接口中的方法
实例演示

public interface CardMapper {
    //查询全部
    @Select("SELECT * FROM card")
    @Results({
        @Result(column = "id",property = "id"),
        @Result(column = "number",property = "number"),
        @Result(
                property = "p",
                javaType = Person.class,
                column = "pid",

                one = @One(select = "demo6.one_to_one.PersonMapper.selectById")
        )
    })
    public abstract List<Card> selectAll();
}

public interface PersonMapper {
    //根据id查询
    @Select("SELECT * FROM person WHERE id=#{id}")
    public abstract Person selectById(Integer id);
}

```
<package name="demo6.one_to_one"/>
```

@Test
    public void selectAll() throws Exception{
        //1.加载核心配置文件
        InputStream is = Resources.getResourceAsStream("MybatisConfig.xml");
        //2.获取SqlSession工厂对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        //3.通过工厂对象获取SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        //4.获取CardMapper接口的实现类对象
        CardMapper mapper = sqlSession.getMapper(CardMapper.class);
        //5.调用实现类的方法，接收结果
        List<Card> list = mapper.selectAll();
        //6.处理结果
        for (Card card : list) {
            System.out.println(card);
        }
        //7.释放资源
        sqlSession.close();
        is.close();
    }

一对多的环境准备
(数据表参考之前映射配置版多表操作)

public class Student {
    private Integer id; //主键id
    private String name; //学生姓名
    private Integer age; //学生年龄

    public Student() {
    }

    public Student(Integer id, String name, Integer age) {
        this.id = id;
        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;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

public class Classes {
    public Integer id; //主键id
    private String name; //班级名称
    private List<Student> students; //班级中所有学生对象

    public Classes() {
    }

    public Classes(Integer id, String name, List<Student> students) {
        this.id = id;
        this.name = name;
        this.students = students;
    }

    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 List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    @Override
    public String toString() {
        return "Classes{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", students=" + students +
                '}';
    }
}

```
<package name="demo6.one_to_many"/>
```
一对多的功能实现
@Results：封装映射关系的父注解
里面有Result[] value()：定义了Result数组
@Result：封装映射关系的子注解
column属性：查询出的表中字段名称
property属性：实体对象中的属性名称
javaType属性：被包含对象的数据类型
many属性：一对多查询固定属性
@Many：一对多查询的注解
select属性：指定调用某个接口中的方法
实例演示

public interface ClassesMapper {
    //查询全部
    @Select("SELECT * FROM classes")
    @Results({
            @Result(column = "id",property = "id"),
            @Result(column = "name",property = "name"),
            @Result(
                    property = "students",   //被包含对象的变量名
                    javaType = List.class, //被包含对象的实际数据类型
                    column = "id",         //根据查询出的classes表的id字段来查询student表
                    many = @Many(select = "demo6.one_to_many.StudentMapper.selectByCid")
            )
    })
    public abstract List<Classes> selectAll();
}

public interface StudentMapper {
    //根据cid查询student表
    @Select("SELECT * FROM student WHERE cid=#{cid}")
    public abstract List<Student> selectByCid(Integer cid);
}

public class Test02 {
    @Test
    public void selectAll() throws Exception {
        //1.加载核心配置文件
        InputStream is = Resources.getResourceAsStream("MybatisConfig.xml");
        //2.获取SqlSession工厂对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        //3.通过工厂对象获取SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        //4.获取ClassesMapper接口的实现类对象
        ClassesMapper mapper = sqlSession.getMapper(ClassesMapper.class);
        //5.调用实现类的方法，接收结果
        List<Classes> list = mapper.selectAll();
        //6.处理结果
        for (Classes cls : list) {
            System.out.println(cls.getId() + "," + cls.getName());
            List<Student> students = cls.getStudents();
            for (Student student : students) {
                System.out.println("\t" + student);
            }
        }
        //7.释放资源
        sqlSession.close();
        is.close();
    }
}

多对多的环境准备
(数据表参考之前映射配置版多表操作)

public class Course {
    private Integer id; //主键id
    private String name;//课程名称

    public Course() {
    }

    public Course(Integer id, String name) {
        this.id = id;
        this.name = name;
    }

    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;
    }

    @Override
    public String toString() {
        return "Course{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

public class Student {
    private Integer id; //主键id
    private String name; //学生姓名
    private Integer age; //学生年龄
    private List<Course> courses; //学生所选择的课程对象

    public Student() {
    }

    public Student(Integer id, String name, Integer age, List<Course> courses) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.courses = courses;
    }

    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 List<Course> getCourses() {
        return courses;
    }

    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", courses=" + courses +
                '}';
    }
}

```
<package name="demo6.many_to_many"/>
```
多对多的功能实现
@Results：封装映射关系的父注解
里面有Result[] value()：定义了Result数组
@Result：封装映射关系的子注解
column属性：查询出的表中字段名称
property属性：实体对象中的属性名称
javaType属性：被包含对象的数据类型
many属性：一对多查询固定属性
@Many：一对多查询的注解
select属性：指定调用某个接口中的方法
实例演示

public interface StudentMapper {
    //查询全部
    @Select("SELECT DISTINCT s.id,s.name,s.age FROM student s,stu_cr sc WHERE sc.sid=s.id")
    @Results({
            @Result(column = "id",property = "id"),
            @Result(column = "name",property = "name"),
            @Result(column = "age",property = "age"),
            @Result(
                    property = "courses",
                    javaType = List.class,
                    column = "id",
                    many = @Many(select = "demo6.many_to_many.CourseMapper.selectBySid")
            )
    })
    public abstract List<Student> selectAll();
}

public interface CourseMapper {
    //根据学生id查询所选课程
    @Select("SELECT c.id,c.name FROM stu_cr sc,course c WHERE sc.cid=c.id AND sc.sid=#{id}")
    public abstract List<Course> selectBySid(Integer sid);
}

public class Test03 {
    @Test
    public void selectAll() throws Exception {
        //1.加载核心配置文件
        InputStream is = Resources.getResourceAsStream("MybatisConfig.xml");
        //2.获取SqlSession工厂对象
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
        //3.通过工厂对象获取SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession(true);
        //4.获取StudentMapper接口的实现类对象
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        //5.调用实现类的方法，接收结果
        List<Student> list = mapper.selectAll();
        //6.处理结果
        for (Student student : list) {
            System.out.println(student.getId() + "," + student.getName()+","+student.getAge());
            List<Course> courses = student.getCourses();
            for (Course cours : courses) {
                System.out.println("\t" + cours);
            }
        }
        //7.释放资源
        sqlSession.close();
        is.close();
    }
}

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Mybatis-注解多表操作

一对一的环境准备

一对一的功能实现

实例演示

一对多的环境准备

一对多的功能实现

实例演示

多对多的环境准备

多对多的功能实现

实例演示

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