Mybatis 注解关联（一对多、多对一）

布满荆棘的人生 2024-02-18 18:02 30阅读 0赞

Mybatis中的一对多、多对一关联关系可以通过xml文档配置，也可以通过annotation注解配置：

以student（多）和school（一）为例：

config.xml:

SchoolMapper.java:

package com.dw.dao;
    
    import org.apache.ibatis.annotations.Many;
    import org.apache.ibatis.annotations.Result;
    import org.apache.ibatis.annotations.Results;
    import org.apache.ibatis.annotations.Select;
    import org.apache.ibatis.mapping.FetchType;
    
    import com.dw.domain.School;
    
    public interface SchoolMapper {
       /**单表查询*/
    	@Select("select * from t_school as sc where sc.sc_id=#{id}")
    	@Results({
    		@Result(column="sc_id",property="id"),
    		@Result(column="sc_name",property="name")
    	})
    	public School selectSchoolById(Integer id);
    	
    	
    	/**一对多 多表查询*/
    	@Select("select * from t_school as sc where sc.sc_id=#{id}")
    	@Results({
    		@Result(column="sc_id",property="id"),
    		@Result(column="sc_name",property="name"),
    		@Result(column="sc_id",property="students",many=@Many(select="com.dw.dao.StudentMapper.selectStudentBySchoolId",fetchType=FetchType.LAZY))
    	})
    	public School selectSchoolById2(Integer id);
    }

StudentMapper.java:

package com.dw.dao;
    
    import java.util.List;
    
    import org.apache.ibatis.annotations.One;
    import org.apache.ibatis.annotations.Result;
    import org.apache.ibatis.annotations.Results;
    import org.apache.ibatis.annotations.Select;
    
    import com.dw.domain.School;
    import com.dw.domain.Student;
    
    public interface StudentMapper {
       /**单表查询*/
    	@Select("select * from t_student as s where s.s_id=#{id}")
    	@Results({
    		@Result(column="s_id",property="id"),
    		@Result(column="s_name",property="name"),
    		@Result(column="s_NO",property="NO")
    	})
    	public Student selectStudentById(Integer id);
    	
    	
    	/**多对一  多表查询*/
    	@Select("select * from t_student as s where s.s_id=#{id}")
    	@Results({
    		@Result(column="s_id",property="id"),
    		@Result(column="s_name",property="name"),
    		@Result(column="s_NO",property="NO"),
    		
    		@Result(column="sc_id",property="school",javaType=School.class,
    		one=@One(select="com.dw.dao.SchoolMapper.selectSchoolById"))
    	})
    	public Student selectStudentById2(Integer id);
    	
    	
    	/**通过学校id查询学生*/
    	@Select("select s.s_id,s.s_name,s.s_NO from t_student as s where s.sc_id=#{id}")
    	@Results({
    		@Result(column="s_id",property="id"),
    		@Result(column="s_name",property="name"),
    		@Result(column="s_NO",property="NO")
    	})
    	public List<Student> selectStudentBySchoolId(Integer id);
    }

测试：

/**school单表查询*/
      @Test
      public void selectSchool4() {
    	  myInit();
    	  School school = schoolMapper.selectSchoolById(1);
    	  System.out.println(school);
    	  destory();
      }
      
      /**student单表查询*/
      @Test
      public void selectStudent4() {
    	  myInit();
    	  Student student = studentMapper.selectStudentById(1);
    	  System.out.println(student);
      }
      
      /**多对一 多表查询*/
      @Test
      public void selectStudent5() {
    	  myInit();
    	  Student student = studentMapper.selectStudentById2(1);
    	  System.out.println(student);
    	  destory();
      }
      
      /**一对多 多表查询*/
      @Test
      public void selectSchool5() {
    	  myInit();
    	  School school = schoolMapper.selectSchoolById2(1);
    	  System.out.println(school);
    	  destory();
      }
      @SuppressWarnings("unused")
    private void myInit() {
    	  try {
    			in = Resources.getResourceAsStream("config.xml");
    			sessionFactory = new SqlSessionFactoryBuilder().build(in);
    			session = sessionFactory.openSession();
    //			userDao = session.getMapper(UserDao.class);
    //			schoolDao = session.getMapper(SchoolDao.class);
    //			studentDao = session.getMapper(StudentDao.class);
    			schoolMapper = session.getMapper(SchoolMapper.class);
    			studentMapper = session.getMapper(StudentMapper.class);
    	} catch (Exception e) {
    		e.printStackTrace();
    	}
      }
      
      @SuppressWarnings("unused")
    private void destory() {
    	  if(session !=null) {
    		  session.close();
    	  }
    	  if(in != null) {
    		  try {
    			in.close();
    		} catch (IOException e) {
    			e.printStackTrace();
    		}
    	  }
      }

School.java:

package com.dw.domain;
    
    import java.util.List;
    
    public class School {
    	private Integer id;
    	private String name;
    	private List<Student> 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 "School [id=" + id + ", name=" + name + ", students=" + students + "]";
    	}
    
    }

Student.java:

package com.dw.domain;
    
    public class Student {
    	private Integer id;
    	private String name;
    	private String NO;
    	private School school;
    
    	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 getNO() {
    		return NO;
    	}
    
    	public void setNO(String nO) {
    		NO = nO;
    	}
    
    	public School getSchool() {
    		return school;
    	}
    
    	public void setSchool(School school) {
    		this.school = school;
    	}
    
    	@Override
    	public String toString() {
    		return "Student [id=" + id + ", name=" + name + ", NO=" + NO + ", school=" + school + "]";
    	}
    
    	
    }