diff --git a/backend/app/http/posts.go b/backend/app/http/posts.go
index 17e4fe6..44bffbd 100644
--- a/backend/app/http/posts.go
+++ b/backend/app/http/posts.go
@@ -267,6 +267,15 @@ func (ctl *posts) Mine(ctx fiber.Ctx, pagination *requests.Pagination, query *Li
 //	@Bind	id path
 //	@Bind	user local
 func (ctl *posts) Buy(ctx fiber.Ctx, id int64, user *model.Users) (*wechat.JSAPIPayParams, error) {
+	bought, err := models.Users.HasBought(ctx.Context(), user.ID, id)
+	if err != nil {
+		return nil, errors.New("查询购买失败")
+	}
+
+	if bought {
+		return nil, errors.New("已经购买过了")
+	}
+
 	post, err := models.Posts.GetByID(ctx.Context(), id)
 	if err != nil {
 		return nil, errors.Wrapf(err, " failed to get post: %d", id)