聊天：最近私聊历史相关逻辑

shared/db/PrivateMessage.ts

@@ -51,6 +51,16 @@ export default class PrivateMessage extends BaseModel {
       const result = await PrivateMessageModel.find({ roomId, seqId: { $lt: fromSeqId } }).sort({ seqId: -1 }).limit(count).lean();
       return result;
     }
+
+    public static async getMsgsByTime(roomId: string, time: Date, count: number) {
+      const result = await PrivateMessageModel.find({ roomId, createdAt: { $gt: time } }).sort({ seqId: -1 }).limit(count).lean();
+      return result;
+    }
+
+    public static async getMsgByRooms(roomIds: string[], count: number) {
+      const result = await PrivateMessageModel.find({ roomId: { $in: roomIds } }).sort({ seqId: -1 }).limit(count).lean();
+      return result;
+    }
 }