feat: 添加媒体资产变体和来源ID字段，支持预览产品与主资产的关联

backend/app/services/media_asset.go

@@ -31,6 +31,11 @@ import (
 //	@provider
 type mediaAsset struct{}
 
+const (
+	mediaAssetVariantMain    = "main"
+	mediaAssetVariantPreview = "preview"
+)
+
 func mediaAssetTransitionAllowed(from, to consts.MediaAssetStatus) bool {
 	switch from {
 	case consts.MediaAssetStatusUploaded:
@@ -77,6 +82,50 @@ func (s *mediaAsset) AdminUploadInit(ctx context.Context, tenantID, operatorUser
 		return nil, errorx.ErrInvalidParameter.WithMsg("invalid type")
 	}
 
+	variant := strings.TrimSpace(strings.ToLower(form.Variant))
+	if variant == "" {
+		variant = mediaAssetVariantMain
+	}
+	if variant != mediaAssetVariantMain && variant != mediaAssetVariantPreview {
+		return nil, errorx.ErrInvalidParameter.WithMsg("invalid variant")
+	}
+
+	var sourceAssetID int64
+	if form.SourceAssetID != nil {
+		sourceAssetID = *form.SourceAssetID
+	}
+	if variant == mediaAssetVariantMain {
+		if sourceAssetID != 0 {
+			return nil, errorx.ErrInvalidParameter.WithMsg("source_asset_id is only allowed for preview variant")
+		}
+	} else {
+		// preview variant: requires a source main asset for traceability.
+		if sourceAssetID <= 0 {
+			return nil, errorx.ErrInvalidParameter.WithMsg("source_asset_id is required for preview variant")
+		}
+		// 校验来源资源存在、同租户、未删除、且为 main 产物。
+		var srcRow struct {
+			Variant string `gorm:"column:variant"`
+		}
+		if err := _db.WithContext(ctx).
+			Table(models.TableNameMediaAsset).
+			Select("variant").
+			Where("tenant_id = ? AND id = ? AND deleted_at IS NULL", tenantID, sourceAssetID).
+			Take(&srcRow).Error; err != nil {
+			if errors.Is(err, gorm.ErrRecordNotFound) {
+				return nil, errorx.ErrRecordNotFound.WithMsg("source media asset not found")
+			}
+			return nil, err
+		}
+		srcVariant := srcRow.Variant
+		if srcVariant == "" {
+			srcVariant = mediaAssetVariantMain
+		}
+		if srcVariant != mediaAssetVariantMain {
+			return nil, errorx.ErrPreconditionFailed.WithMsg("source asset must be main variant")
+		}
+	}
+
 	objectKey, err := newObjectKey(tenantID, operatorUserID, typ, now)
 	if err != nil {
 		return nil, pkgerrors.Wrap(err, "generate object_key failed")
@@ -113,11 +162,27 @@ func (s *mediaAsset) AdminUploadInit(ctx context.Context, tenantID, operatorUser
 		return nil, pkgerrors.Wrap(err, "create media asset failed")
 	}
 
+	// variant/source_asset_id 目前为 DB 新增字段；由于 models 为 gen 产物，这里用 SQL 更新列值。
+	updates := map[string]any{
+		"variant": variant,
+	}
+	if sourceAssetID > 0 {
+		updates["source_asset_id"] = sourceAssetID
+	}
+	if err := _db.WithContext(ctx).
+		Model(&models.MediaAsset{}).
+		Where("id = ? AND tenant_id = ?", m.ID, tenantID).
+		Updates(updates).Error; err != nil {
+		return nil, pkgerrors.Wrap(err, "update media asset variant/source_asset_id failed")
+	}
+
 	logrus.WithFields(logrus.Fields{
 		"tenant_id":  tenantID,
 		"user_id":    operatorUserID,
 		"asset_id":   m.ID,
 		"type":       typ,
+		"variant":    variant,
+		"source_id":  sourceAssetID,
 		"object_key": objectKey,
 	}).Info("services.media_asset.admin.upload_init")