fix: 完善学校管理删除逻辑 - 参照旧版本修复

根据旧版本代码修复删除逻辑：
- 删除学校前检查是否有年级，有则提示"请先删除年级"
- 删除年级前检查是否有班级，有则提示"请先删除班级"
- 树形数据添加 gradeId、classId 字段
- TODO: 学生管理模块完成后添加学生引用检查

backend/ruoyi-modules/pangu-business/src/main/java/org/dromara/pangu/school/domain/vo/SchoolTreeNode.java

@@ -81,4 +81,14 @@ public class SchoolTreeNode {
      * 学校年级关联ID（班级节点需要）
      */
     private Long schoolGradeId;
+
+    /**
+     * 年级ID（仅年级节点有值）
+     */
+    private Long gradeId;
+
+    /**
+     * 班级ID（仅班级节点有值）
+     */
+    private Long classId;
 }

backend/ruoyi-modules/pangu-business/src/main/java/org/dromara/pangu/school/service/impl/PgSchoolServiceImpl.java

@@ -126,7 +126,20 @@ public class PgSchoolServiceImpl implements IPgSchoolService {
     }
 
     @Override
+    @Transactional(rollbackFor = Exception.class)
     public int deleteByIds(Long[] schoolIds) {
+        for (Long schoolId : schoolIds) {
+            // 1. 检查是否有年级
+            Long gradeCount = schoolGradeMapper.selectCount(
+                new LambdaQueryWrapper<PgSchoolGrade>().eq(PgSchoolGrade::getSchoolId, schoolId)
+            );
+            if (gradeCount > 0) {
+                PgSchool school = baseMapper.selectById(schoolId);
+                String schoolName = school != null ? school.getSchoolName() : schoolId.toString();
+                throw new RuntimeException("学校\"" + schoolName + "\"下存在年级数据，请先删除年级");
+            }
+            // TODO: 检查是否被学生信息引用（学生管理模块完成后添加）
+        }
         return baseMapper.deleteByIds(Arrays.asList(schoolIds));
     }
 
@@ -193,17 +206,22 @@ public class PgSchoolServiceImpl implements IPgSchoolService {
     @Override
     @Transactional(rollbackFor = Exception.class)
     public int removeSchoolGrade(Long schoolGradeId) {
-        // 先删除该年级下的所有班级
-        schoolClassMapper.delete(
-            new LambdaQueryWrapper<PgSchoolClass>()
-                .eq(PgSchoolClass::getSchoolGradeId, schoolGradeId)
+        // 1. 检查是否有班级
+        Long classCount = schoolClassMapper.selectCount(
+            new LambdaQueryWrapper<PgSchoolClass>().eq(PgSchoolClass::getSchoolGradeId, schoolGradeId)
         );
-        // 再删除年级
+        if (classCount > 0) {
+            throw new RuntimeException("该年级下存在班级数据，请先删除班级");
+        }
+        // TODO: 检查是否被学生信息引用（学生管理模块完成后添加）
+        
+        // 2. 删除年级
         return schoolGradeMapper.deleteById(schoolGradeId);
     }
 
     @Override
     public int removeGradeClass(Long schoolClassId) {
+        // TODO: 检查是否被学生信息引用（学生管理模块完成后添加）
         return schoolClassMapper.deleteById(schoolClassId);
     }
 
@@ -294,6 +312,7 @@ public class PgSchoolServiceImpl implements IPgSchoolService {
                     gradeNode.setSchoolId(sg.getSchoolId());
                     gradeNode.setParentId(s.getSchoolId());
                     gradeNode.setSchoolGradeId(sg.getId());
+                    gradeNode.setGradeId(sg.getGradeId());
 
                     // 查找该年级的班级
                     List<SchoolTreeNode> classNodes = allSchoolClasses.stream()
@@ -306,6 +325,7 @@ public class PgSchoolServiceImpl implements IPgSchoolService {
                             classNode.setSchoolId(sc.getSchoolId());
                             classNode.setSchoolGradeId(sc.getSchoolGradeId());
                             classNode.setParentId(sg.getId());
+                            classNode.setClassId(sc.getClassId());
                             return classNode;
                         })
                         .toList();