feat(repository): enhance repository methods with batch processing and transaction support

- Updated Like and Unlike methods in CommentRepository to use transactions for data consistency.
- Introduced IsLikedBatch method for batch checking if comments are liked, addressing N+1 query issues.
- Enhanced BatchDelete method in PostRepository to perform batch deletions within a single transaction, improving efficiency.
- Added BatchUpdateStatus method for posts to utilize a single SQL update for status changes, reducing database load.
- Implemented BatchUpdateSortOrder in StickerRepository using CASE WHEN for efficient sorting updates.
- Added IsFollowingBatch and IsBlockedBatch methods in UserRepository for batch checking follow and block relationships, optimizing performance.

internal/repository/group_repo.go

@@ -4,6 +4,7 @@ import (
 	"carrot_bbs/internal/model"
 	"carrot_bbs/internal/pkg/cursor"
 	"context"
+	"errors"
 
 	"gorm.io/gorm"
 )
@@ -188,6 +189,36 @@ func (r *groupRepository) IsMember(groupID string, userID string) (bool, error)
 	return count > 0, err
 }
 
+// GetExistingMembers 批量检查用户是否是群成员（解决 N+1 问题）
+// 返回 map[userID]bool
+func (r *groupRepository) GetExistingMembers(groupID string, userIDs []string) (map[string]bool, error) {
+	result := make(map[string]bool)
+	if len(userIDs) == 0 || groupID == "" {
+		return result, nil
+	}
+
+	// 初始化所有用户为 false
+	for _, id := range userIDs {
+		result[id] = false
+	}
+
+	// 一次性查询所有群成员记录
+	var existingIDs []string
+	err := r.db.Model(&model.GroupMember{}).
+		Where("group_id = ? AND user_id IN ?", groupID, userIDs).
+		Pluck("user_id", &existingIDs).Error
+	if err != nil {
+		return nil, err
+	}
+
+	// 更新已存在的成员
+	for _, id := range existingIDs {
+		result[id] = true
+	}
+
+	return result, nil
+}
+
 // GetUserGroups 获取用户加入的群组列表
 func (r *groupRepository) GetUserGroups(userID string, page, pageSize int) ([]model.Group, int64, error) {
 	var groups []model.Group
@@ -318,7 +349,7 @@ func (r *groupRepository) GetLatestAnnouncement(groupID string) (*model.GroupAnn
 		Order("is_pinned DESC, created_at DESC").
 		First(&announcement).Error
 	if err != nil {
-		if err == gorm.ErrRecordNotFound {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
 			return nil, nil
 		}
 		return nil, err