From 4cc0713459e32ebf29f498609db2af27e7e152fe Mon Sep 17 00:00:00 2001
From: hhs <386998068@qq.com>
Date: Mon, 22 Jun 2026 12:39:37 +0800
Subject: [PATCH] =?UTF-8?q?fix:=20=E4=BF=AE=E5=A4=8D=E7=A9=BA=E4=BC=9A?=
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 =?UTF-8?q?=E5=89=8D=E7=AB=AF=E5=B4=A9=E6=BA=83=E7=9A=84=E9=97=AE=E9=A2=98?=
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## 问题描述
当用户创建新会话但未发送任何消息就切换到其他会话时，前端控制台报错：
"TypeError: Cannot read properties of null (reading 'map')"

根本原因：Go 后端未初始化的切片序列化为 JSON 时会变成 `null` 而非 `[]`，
前端尝试对 `null` 调用 `.map()` 导致崩溃。

## 修复方案
采用多层防御策略，同时修复后端和前端：

### 后端修复（确保 API 契约正确）
1. message_pg.go:93 - 将 `var messages []StoredMessage` 改为
   `messages := make([]StoredMessage, 0)`，确保空结果序列化为 `[]`
2. conversation.go - 在两个响应路径（PG 查询 + 内存回退）添加防御性 nil 检查

### 前端防御（多层保护）
1. useSessionList.ts - 在 loadMessages 和 loadSessions 中添加 null 合并操作
   `(res.data.messages || [])` 确保即使后端退化也不会崩溃

## 影响范围
- 所有空会话（新建后未发送消息的对话）现在可以正常切换
- API 响应符合 JSON 最佳实践（数组字段永远是 `[]` 而非 `null`）
---
 backend/internal/api/conversation.go | 6 ++++++
 backend/internal/store/message_pg.go | 2 +-
 frontend/src/hooks/useSessionList.ts | 4 ++--
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/backend/internal/api/conversation.go b/backend/internal/api/conversation.go
index c3eed70..e21471a 100644
--- a/backend/internal/api/conversation.go
+++ b/backend/internal/api/conversation.go
@@ -273,6 +273,9 @@ func (h *ConversationHandler) GetMessages(c *gin.Context) {
 			return
 		}
 		count, _ := h.msgRepo.GetMessageCount(c.Request.Context(), sessionID)
+		if messages == nil {
+			messages = []store.StoredMessage{}
+		}
 		c.JSON(http.StatusOK, gin.H{
 			"messages": messages,
 			"total":    count,
@@ -314,6 +317,9 @@ func (h *ConversationHandler) GetMessages(c *gin.Context) {
 	}
 	messages := allMessages[start:]
 
+	if messages == nil {
+		messages = []models.Message{}
+	}
 	c.JSON(http.StatusOK, gin.H{
 		"messages": messages,
 		"total":    total,
diff --git a/backend/internal/store/message_pg.go b/backend/internal/store/message_pg.go
index 014194b..b393c9c 100644
--- a/backend/internal/store/message_pg.go
+++ b/backend/internal/store/message_pg.go
@@ -90,7 +90,7 @@ func (r *PgMessageRepository) queryMessages(ctx context.Context, query string, a
 	}
 	defer pgxRows.Close()
 
-	var messages []StoredMessage
+	messages := make([]StoredMessage, 0)
 	for pgxRows.Next() {
 		var m StoredMessage
 		if err := pgxRows.Scan(&m.ID, &m.SessionID, &m.Role, &m.Content, &m.TokensUsed, &m.CreatedAt); err != nil {
diff --git a/frontend/src/hooks/useSessionList.ts b/frontend/src/hooks/useSessionList.ts
index 841a3e4..c33e212 100644
--- a/frontend/src/hooks/useSessionList.ts
+++ b/frontend/src/hooks/useSessionList.ts
@@ -80,7 +80,7 @@ export function useSessionList(accessToken?: string | null) {
     try {
       const res = await listConversations(accessToken);
       if (res.data) {
-        const list = res.data.conversations.map(toSessionSummary);
+        const list = (res.data.conversations || []).map(toSessionSummary);
         setSessions(list);
         // 恢复上次选中的会话（如果仍然存在）
         const lastId = localStorage.getItem(LAST_ACTIVE_KEY);
@@ -193,7 +193,7 @@ export function useSessionList(accessToken?: string | null) {
       try {
         const res = await getConversationMessages(accessToken, sessionId);
         if (res.data) {
-          return res.data.messages.map(toChatMessage);
+          return (res.data.messages || []).map(toChatMessage);
         }
       } catch (err) {
         console.error("[SessionList] 加载消息失败:", err);