fix: GET /school/classes 班级列表关联教师已删除时不抛异常

- 新增 TeacherService.findTeacherById 教师不存在时返回 null
- SchoolClassController 使用 findTeacherById 替代 getTeacherById

Made-with: Cursor

reading-platform-java/src/main/java/com/reading/platform/controller/school/SchoolClassController.java

@@ -94,7 +94,7 @@ public class SchoolClassController {
                     new LambdaQueryWrapper<ClassTeacher>().eq(ClassTeacher::getClassId, vo.getId()));
             List<ClassTeacherResponse> teacherList = new ArrayList<>();
             for (ClassTeacher ct : classTeachers) {
-                Teacher t = teacherService.getTeacherById(ct.getTeacherId());
+                Teacher t = teacherService.findTeacherById(ct.getTeacherId());
                 teacherList.add(ClassTeacherResponse.builder()
                         .id(ct.getId())
                         .classId(ct.getClassId())
@@ -157,7 +157,7 @@ public class SchoolClassController {
                 new LambdaQueryWrapper<ClassTeacher>().eq(ClassTeacher::getClassId, id));
         List<ClassTeacherResponse> teacherList = new ArrayList<>();
         for (ClassTeacher ct : classTeachers) {
-            Teacher t = teacherService.getTeacherById(ct.getTeacherId());
+            Teacher t = teacherService.findTeacherById(ct.getTeacherId());
             teacherList.add(ClassTeacherResponse.builder()
                     .id(ct.getId())
                     .classId(ct.getClassId())

reading-platform-java/src/main/java/com/reading/platform/service/TeacherService.java

@@ -34,6 +34,11 @@ public interface TeacherService extends IService<Teacher> {
      */
     Teacher getTeacherById(Long id);
 
+    /**
+     * 根据 ID 查询教师，不存在时返回 null（不抛异常）
+     */
+    Teacher findTeacherById(Long id);
+
     /**
      * 根据 ID 查询教师（带租户验证）
      */

reading-platform-java/src/main/java/com/reading/platform/service/impl/TeacherServiceImpl.java

@@ -160,6 +160,12 @@ public class TeacherServiceImpl extends com.baomidou.mybatisplus.extension.servi
         return teacher;
     }
 
+    @Override
+    public Teacher findTeacherById(Long id) {
+        if (id == null) return null;
+        return teacherMapper.selectById(id);
+    }
+
     @Override
     public Teacher getTeacherByIdWithTenantCheck(Long id, Long tenantId) {
         log.debug("查询教师（带租户验证），ID: {}, tenantId: {}", id, tenantId);