feat: 添加作品购买人列表功能

backend_v1/app/services/posts.go

@@ -127,6 +127,62 @@ func (m *posts) Bought(ctx context.Context, userId int64, pagination *requests.P
 	}, nil
 }
 
+// Buyers 获取某个作品的购买人列表（管理端使用）
+func (m *posts) Buyers(ctx context.Context, postID int64, pagination *requests.Pagination) (*requests.Pager, error) {
+	pagination.Format()
+
+	// 先分页查询购买记录，避免一次性拉取全量 user_posts 造成内存/延迟抖动
+	tblUserPost, queryUserPost := models.UserPostQuery.QueryContext(ctx)
+	queryUserPost = queryUserPost.
+		Where(tblUserPost.PostID.Eq(postID)).
+		Order(tblUserPost.CreatedAt.Desc())
+
+	userPosts, cnt, err := queryUserPost.FindByPage(int(pagination.Offset()), int(pagination.Limit))
+	if err != nil {
+		return nil, err
+	}
+	if len(userPosts) == 0 {
+		return &requests.Pager{
+			Items:      []dto.PostBuyerItem{},
+			Total:      cnt,
+			Pagination: *pagination,
+		}, nil
+	}
+
+	// 批量回表查询用户信息，避免 N+1
+	userIDs := lo.Uniq(lo.Map(userPosts, func(item *models.UserPost, _ int) int64 {
+		return item.UserID
+	}))
+	tblUser, queryUser := models.UserQuery.QueryContext(ctx)
+	users, err := queryUser.Where(tblUser.ID.In(userIDs...)).Find()
+	if err != nil {
+		return nil, err
+	}
+	userMap := lo.KeyBy(users, func(item *models.User) int64 { return item.ID })
+
+	items := make([]dto.PostBuyerItem, 0, len(userPosts))
+	for _, item := range userPosts {
+		user, ok := userMap[item.UserID]
+		if !ok {
+			continue
+		}
+		items = append(items, dto.PostBuyerItem{
+			UserID:   user.ID,
+			Username: user.Username,
+			Avatar:   user.Avatar,
+			Phone:    user.Phone,
+			BoughtAt: item.CreatedAt,
+			Price:    item.Price,
+		})
+	}
+
+	return &requests.Pager{
+		Items:      items,
+		Total:      cnt,
+		Pagination: *pagination,
+	}, nil
+}
+
 // GetPostsMapByIDs
 func (m *posts) GetPostsMapByIDs(ctx context.Context, ids []int64) (map[int64]*models.Post, error) {
 	tbl, query := models.PostQuery.QueryContext(ctx)