fix: harden explore dataset collection

backend/internal/logic/dataset/service.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
 	"senlinai-agent/backend/internal/models"
 )
 
@@ -326,24 +327,20 @@ func (s *Service) storeFeedItems(userID uint, source models.SaDatasetSource, ite
 	inserted := 0
 	err := s.db.Transaction(func(tx *gorm.DB) error {
 		for _, input := range items {
-			var count int64
-			if err := tx.Model(&models.SaDatasetItem{}).
-				Where("source_id = ? AND external_id = ?", source.ID, input.ExternalID).
-				Count(&count).Error; err != nil {
-				return err
-			}
-			if count > 0 {
-				continue
-			}
+			externalID := input.ExternalID
 			item := models.SaDatasetItem{
-				SourceID: source.ID, CreatedBy: userID, ExternalID: input.ExternalID,
+				SourceID: source.ID, CreatedBy: userID, ExternalID: &externalID,
 				Title: input.Title, Summary: input.Summary, Content: input.Content,
 				URL: input.URL, Status: "unread", PublishedAt: input.PublishedAt,
 			}
-			if err := tx.Create(&item).Error; err != nil {
-				return err
+			result := tx.Clauses(clause.OnConflict{
+				Columns:   []clause.Column{{Name: "source_id"}, {Name: "external_id"}},
+				DoNothing: true,
+			}).Create(&item)
+			if result.Error != nil {
+				return result.Error
 			}
-			inserted++
+			inserted += int(result.RowsAffected)
 		}
 		return nil
 	})