fixed bug：如果讲师有关联的课程，则不可被删除

src/main/java/com/qkdata/biz/management/service/TeacherService.java

@@ -123,6 +123,10 @@ public class TeacherService extends ServiceImpl<TeacherMapper, TeacherPO> {
     @Transactional
     public void removeTeachers(List<Long> ids) {
         for (Long id : ids){
+            int count = courseService.countByTeacher(id);
+            if (count > 0){
+                throw new BusinessException("该讲师已有关联课程，不可删除");
+            }
             TeacherPO teacherPO = getById(id);
             removeById(id);
             //删除讲师帐号