Person
package com.yyl.bean; 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 + '}'; } }
Student
package com.yyl.bean; import java.util.List; 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 List<Course> getCourses() { return courses; } public void setCourses(List<Course> courses) { 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; } @Override public String toString() { return "Student{" + "id=" + id + ", name='" + name + '\'' + ", age=" + age + '}'; } }
2. 一对一查询
2.1 一对一查询的模型
一对一查询的需求：查询一个用户信息，与此同时查询出该用户对应的身份证信息
2.2 一对一查询的语句
对应的sql语句：
SELECT * FROM card； SELECT * FROM person WHERE id=#{id};
2.3 创建PersonMapper接口
public interface PersonMapper { //根据id查询 @Select("SELECT * FROM person WHERE id=#{id}") public abstract Person selectById(Integer id); }
2.4 使用注解配置Mapper
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", // 被包含对象的变量名 javaType = Person.class, // 被包含对象的实际数据类型 column = "pid", // 根据查询出的card表中的pid字段来查询person表 /* one、@One 一对一固定写法 select属性：指定调用哪个接口中的哪个方法 */ one = @One(select = "com.yyl.one_to_one.PersonMapper.selectById") ) }) public abstract List<Card> selectAll(); }
2.5 测试类
public class Test01 { @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对象 SqlSession sqlSession = sqlSessionFactory.openSession(true); //4.获取CardMapper接口的实现类对象 CardMapper mapper = sqlSession.getMapper(CardMapper.class); //5.调用实现类对象中的方法，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(); } }
运行结果如下：
2.6 一对一配置总结
3. 一对多查询
3.1 一对多查询的模型
一对多查询的需求：查询一个课程，与此同时查询出该该课程对应的学生信息
3.2 一对多查询的语句
对应的sql语句：
SELECT * FROM classes SELECT * FROM student WHERE cid=#{cid}
3.3 创建StudentMapper接口
public interface StudentMapper { //根据cid查询student表 @Select("SELECT * FROM student WHERE cid=#{cid}") public abstract List<Student> selectByCid(Integer cid); }
3.4 使用注解配置Mapper
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 一对多查询的固定写法 select属性：指定调用哪个接口中的哪个查询方法 */ many = @Many(select = "com.yyl.one_to_many.StudentMapper.selectByCid") ) }) public abstract List<Classes> selectAll(); }
3.5 测试类
public class Test01 { @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对象 SqlSession sqlSession = sqlSessionFactory.openSession(true); //4.获取ClassesMapper接口的实现类对象 ClassesMapper mapper = sqlSession.getMapper(ClassesMapper.class); //5.调用实现类对象中的方法，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(); } }
运行结果如下：
3.6 一对多配置总结
4. 多对多查询
4.1 多对多查询的模型
多对多查询的需求：查询学生以及所对应的课程信息
4.2 多对多查询的语句
对应的sql语句：
SELECT DISTINCT s.id,s.name,s.age FROM student s,stu_cr sc WHERE sc.sid=s.id SELECT c.id,c.name FROM stu_cr sc,course c WHERE sc.cid=c.id AND sc.sid=#{id}
4.3 添加CourseMapper 接口方法
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 id); }
4.4 使用注解配置Mapper
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", // 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student表的id来作为关联条件，去查询中间表和课程表 /* many、@Many 一对多查询的固定写法 select属性：指定调用哪个接口中的哪个查询方法 */ many = @Many(select = "com.yyl.many_to_many.CourseMapper.selectBySid") ) }) public abstract List<Student> selectAll(); }
4.5 测试类
public class Test01 { @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对象 SqlSession sqlSession = sqlSessionFactory.openSession(true); //4.获取StudentMapper接口的实现类对象 StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); //5.调用实现类对象中的方法，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(); } }
运行结果如下：
4.6 多对多配置总结
