refactor(classes): preserve student membership history

apps/server/src/classes/classes.service.ts

@@ -227,34 +227,45 @@ export class ClassesService {
     }
 
     // 3. Fetch existing class-student links in one query
-    const allStudentIds = Array.from(dingToStudentId.values());
-    const alreadyInClass = new Set<number>();
-    if (allStudentIds.length > 0) {
-      const existingClassStudents = await this.classStudentRepo.find({
-        where: { classId, studentId: In(allStudentIds) },
-      });
-      for (const cs of existingClassStudents) {
-        alreadyInClass.add(cs.studentId);
+    const allStudentIds = Array.from(new Set(dingToStudentId.values()));
+    const existingClassStudents =
+      allStudentIds.length > 0
+        ? await this.classStudentRepo.find({
+            where: { classId, studentId: In(allStudentIds) },
+          })
+        : [];
+    const existingByStudentId = new Map(
+      existingClassStudents.map((classStudent) => [classStudent.studentId, classStudent]),
+    );
+    const today = new Date().toISOString().slice(0, 10);
+    let skipped = 0;
+    const memberships = allStudentIds.flatMap((studentId) => {
+      const existing = existingByStudentId.get(studentId);
+      if (existing?.status === 'active') {
+        skipped++;
+        return [];
       }
-    }
-
-    // 4. Batch insert new class-student records
-    const newClassStudents = allStudentIds
-      .filter((sid) => !alreadyInClass.has(sid))
-      .map((studentId) =>
+      if (existing) {
+        existing.status = 'active';
+        existing.joinDate = today;
+        existing.leaveDate = null;
+        return [existing];
+      }
+      return [
         this.classStudentRepo.create({
           classId,
           studentId,
           status: 'active',
-          joinDate: new Date().toISOString().slice(0, 10),
+          joinDate: today,
         }),
-      );
+      ];
+    });
 
-    if (newClassStudents.length > 0) {
-      await this.classStudentRepo.save(newClassStudents);
+    if (memberships.length > 0) {
+      await this.classStudentRepo.save(memberships);
     }
 
-    return { imported: newClassStudents.length, skipped: alreadyInClass.size };
+    return { imported: memberships.length, skipped };
   }
   async update(id: number, dto: UpdateClassDto) {
     const cls = await this.classRepo.findOne({ where: { id } });
@@ -315,26 +326,61 @@ export class ClassesService {
   }
 
   async addStudents(classId: number, studentIds: number[]) {
+    const uniqueStudentIds = [...new Set(studentIds)];
+    if (uniqueStudentIds.length === 0) return { added: 0, skipped: 0 };
+
+    const cls = await this.classRepo.findOne({ where: { id: classId } });
+    if (!cls) throw new NotFoundException('班级不存在');
+
+    const students = await this.studentRepo.find({ where: { id: In(uniqueStudentIds) } });
+    if (students.length !== uniqueStudentIds.length) {
+      throw new NotFoundException('部分学生不存在');
+    }
+
     const existing = await this.classStudentRepo.find({
-      where: { classId, studentId: In(studentIds) },
+      where: { classId, studentId: In(uniqueStudentIds) },
     });
-    const existingIds = new Set(existing.map((e) => e.studentId));
-    const newIds = studentIds.filter((id) => !existingIds.has(id));
-
-    const entries = newIds.map((sid) =>
-      this.classStudentRepo.create({
-        classId,
-        studentId: sid,
-        joinDate: new Date().toISOString().split('T')[0],
-      }),
+    const existingByStudentId = new Map(
+      existing.map((classStudent) => [classStudent.studentId, classStudent]),
     );
-    if (entries.length) await this.classStudentRepo.save(entries);
+    const today = new Date().toISOString().split('T')[0];
+    let skipped = 0;
+    const memberships = uniqueStudentIds.flatMap((studentId) => {
+      const current = existingByStudentId.get(studentId);
+      if (current?.status === 'active') {
+        skipped++;
+        return [];
+      }
+      if (current) {
+        current.status = 'active';
+        current.joinDate = today;
+        current.leaveDate = null;
+        return [current];
+      }
+      return [
+        this.classStudentRepo.create({
+          classId,
+          studentId,
+          status: 'active',
+          joinDate: today,
+        }),
+      ];
+    });
+    if (memberships.length) await this.classStudentRepo.save(memberships);
 
-    return { added: entries.length, skipped: studentIds.length - entries.length };
+    return { added: memberships.length, skipped };
   }
 
   async removeStudent(classId: number, studentId: number) {
-    await this.classStudentRepo.delete({ classId, studentId });
+    const membership = await this.classStudentRepo.findOne({
+      where: { classId, studentId },
+    });
+    if (!membership) throw new NotFoundException('学生不在该班级');
+    if (membership.status !== 'active') throw new BadRequestException('学生已离班');
+
+    membership.status = 'left';
+    membership.leaveDate = new Date().toISOString().split('T')[0];
+    await this.classStudentRepo.save(membership);
     return { success: true };
   }