使用注解实现mybatis查询

╰半夏微凉° 2022-05-10 06:58 230阅读 0赞

mybatis.xml

mapper.java 增删改查

public interface TeacherMapper {
    	@Select("select * from teacher")
    	List<Teacher> selAll();
    	@Insert("insert into teacher (id,name) values(default,#{name})")
    	int insTeacher(Teacher teacher);
    	@Update("update teacher set name=#{name} where id=#{id}")
    	int updTeacher(Teacher teacher);
    	@Delete("delete from teacher where id=#{0}")
    	int delById(int id);
    }

测试代码

TeacherMapper mapper = session.getMapper(TeacherMapper.class);			
    List<Teacher> list = mapper.selAll();

结果

Teacher [id=1, name=老师1, list=null]
    Teacher [id=2, name=老师2, list=null]
    Teacher [id=3, name=老师3, list=null]

mapper.java 多表联合查询，实现resultMap功能

public interface StudentMapper {
    	@Select("select * from student where tid=#{0}")
    	Student selById(int id);
    	
    }
    public interface TeacherMapper {
    	@Results(value= {
    		@Result(id=true,property="id",column="id"),
    		@Result(property="name",column="name"),
    		@Result(property="list",column="id",many=@Many(select="com.bjsxt.mapper.StudentMapper.selByTid"))
    	})	
    	@Select("select * from teacher")
    	List<Teacher> selTeacher();
    }
    @results（）相对于<resultMap>
    @result（）相当于<id>或<result>
    @result（id=true）相当于<id>
    @Many（）相当于<collection>
    @One（）相当于<association>

测试代码

List<Teacher> list = mapper.selTeacher();
    for(Teacher tea:list) {
    	System.out.println(tea);
    }

结果

Teacher [id=1, name=老师1, list=[Student [id=1, name=学生1, age=11, tid=1, teacher=null], Student [id=2, name=学生2, age=16, tid=1, teacher=null], Student [id=3, name=学生3, age=17, tid=1, teacher=null]]]
    Teacher [id=2, name=老师2, list=[Student [id=4, name=学生4, age=18, tid=2, teacher=null], Student [id=5, name=学生5, age=19, tid=2, teacher=null]]]
    Teacher [id=3, name=老师3, list=[Student [id=6, name=学生6, age=22, tid=3, teacher=null]]]
    Teacher [id=13, name=Tom, list=[]]
    Teacher [id=23, name=Mac, list=[]]