feat: 支持章节通过 mid 进行访问，优化阅读跳转逻辑。新增章节数据结构，包含章节的 mid 信息，提升用户体验。更新 API 以支持通过 mid 查询章节内容，确保兼容性与灵活性。

soul-api/internal/handler/book.go

@@ -22,16 +22,40 @@ func BookAllChapters(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"success": true, "data": list})
 }
 
-// BookChapterByID GET /api/book/chapter/:id
-// 同时兼容小程序：将 content/chapterTitle/partTitle 等放到顶层，便于 miniprogram 直接 res.content
+// BookChapterByID GET /api/book/chapter/:id  按业务 id 查询（兼容旧链接）
 func BookChapterByID(c *gin.Context) {
 	id := c.Param("id")
 	if id == "" {
 		c.JSON(http.StatusBadRequest, gin.H{"success": false, "error": "缺少 id"})
 		return
 	}
+	findChapterAndRespond(c, func(db *gorm.DB) *gorm.DB {
+		return db.Where("id = ?", id)
+	})
+}
+
+// BookChapterByMID GET /api/book/chapter/by-mid/:mid  按自增主键 mid 查询（新链接推荐）
+func BookChapterByMID(c *gin.Context) {
+	midStr := c.Param("mid")
+	if midStr == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"success": false, "error": "缺少 mid"})
+		return
+	}
+	mid, err := strconv.Atoi(midStr)
+	if err != nil || mid < 1 {
+		c.JSON(http.StatusBadRequest, gin.H{"success": false, "error": "mid 必须为正整数"})
+		return
+	}
+	findChapterAndRespond(c, func(db *gorm.DB) *gorm.DB {
+		return db.Where("mid = ?", mid)
+	})
+}
+
+// findChapterAndRespond 按条件查章节并返回统一格式
+func findChapterAndRespond(c *gin.Context, whereFn func(*gorm.DB) *gorm.DB) {
 	var ch model.Chapter
-	if err := database.DB().Where("id = ?", id).First(&ch).Error; err != nil {
+	db := database.DB()
+	if err := whereFn(db).First(&ch).Error; err != nil {
 		if err == gorm.ErrRecordNotFound {
 			c.JSON(http.StatusNotFound, gin.H{"success": false, "error": "章节不存在"})
 			return
@@ -39,14 +63,14 @@ func BookChapterByID(c *gin.Context) {
 		c.JSON(http.StatusOK, gin.H{"success": false, "error": err.Error()})
 		return
 	}
-	// 返回格式：顶层携带 content/chapterTitle/partTitle 等，供小程序 read 页直接使用
 	out := gin.H{
-		"success":     true,
-		"data":        ch,
-		"content":     ch.Content,
+		"success":      true,
+		"data":         ch,
+		"content":      ch.Content,
 		"chapterTitle": ch.ChapterTitle,
-		"partTitle":   ch.PartTitle,
-		"id":          ch.ID,
+		"partTitle":    ch.PartTitle,
+		"id":           ch.ID,
+		"mid":          ch.MID,
 		"sectionTitle": ch.SectionTitle,
 	}
 	if ch.IsFree != nil {
@@ -193,7 +217,7 @@ func BookSearch(c *gin.Context) {
 			matchType = "title"
 		}
 		results = append(results, gin.H{
-			"id": ch.ID, "title": ch.SectionTitle, "part": ch.PartTitle, "chapter": ch.ChapterTitle,
+			"id": ch.ID, "mid": ch.MID, "title": ch.SectionTitle, "part": ch.PartTitle, "chapter": ch.ChapterTitle,
 			"isFree": ch.IsFree, "matchType": matchType,
 		})
 	}