diff --git a/apps/server/package.json b/apps/server/package.json
index d40c28b..95526d5 100644
--- a/apps/server/package.json
+++ b/apps/server/package.json
@@ -6,8 +6,9 @@
   "license": "UNLICENSED",
   "author": "",
   "scripts": {
-    "dev": "nest start --watch -p tsconfig.build.json",
-    "build": "nest build",
+    "dev": "SEED_DEV=true nest start --watch -p tsconfig.build.json",
+    "build": "nest build -p tsconfig.build.json",
+    "start:dev": "SEED_DEV=true nest start --watch",
     "format": "oxfmt",
     "start": "nest start",
     "start:dev": "nest start --watch",
diff --git a/apps/server/src/entities/user-ding-mapping.entity.ts b/apps/server/src/entities/user-ding-mapping.entity.ts
new file mode 100644
index 0000000..f927a39
--- /dev/null
+++ b/apps/server/src/entities/user-ding-mapping.entity.ts
@@ -0,0 +1,52 @@
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  CreateDateColumn,
+  UpdateDateColumn,
+  Index,
+  ManyToOne,
+  JoinColumn,
+} from 'typeorm';
+import { User } from './user.entity';
+
+/**
+ * Maps DingTalk user IDs to local User records.
+ * Used for incremental sync and attendance auto-matching.
+ *
+ * Mapping chain:
+ *   dingtalk userid → UserDingMapping.dingUserId → UserDingMapping.userId
+ *   → User.id → Student.userId → Student.id
+ *   → DingAttendanceRaw.dingUserId → UserDingMapping.dingUserId → auto-match
+ */
+@Entity('user_ding_mapping')
+export class UserDingMapping {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  /** DingTalk user ID (from DingTalk API) */
+  @Column({ name: 'ding_user_id', length: 100, unique: true })
+  dingUserId: string;
+
+  /** Local User ID */
+  @Column({ name: 'user_id', type: 'integer', unique: true })
+  userId: number;
+
+  @ManyToOne(() => User, { onDelete: 'CASCADE' })
+  @JoinColumn({ name: 'user_id' })
+  user: User;
+
+  /** DingTalk user name (cached for display) */
+  @Column({ name: 'ding_name', length: 100, nullable: true })
+  dingName: string;
+
+  /** DingTalk mobile (cached for display) */
+  @Column({ name: 'ding_mobile', length: 20, nullable: true })
+  dingMobile: string;
+
+  @CreateDateColumn({ name: 'created_at' })
+  createdAt: Date;
+
+  @UpdateDateColumn({ name: 'updated_at' })
+  updatedAt: Date;
+}