H-137: fix computed article distance mapping (#22)

Co-authored-by: Rogee <rogee@ipao.vip>

backend/internal/model/article.go

@@ -24,7 +24,7 @@ type Article struct {
 	AssociatedArticleID *uint           `gorm:"index" json:"associated_article_id,omitempty"` // translations: root article
 	Meta                json.RawMessage `gorm:"type:jsonb;serializer:json" json:"meta"`
 	CustomAttributes    json.RawMessage `gorm:"type:jsonb;serializer:json" json:"custom_attributes"`
-	SemanticDistance    *float64        `gorm:"column:semantic_distance;->;-:migration" json:"-"`
+	SemanticDistance    *float64        `gorm:"-" json:"-"`
 
 	Portal             Portal    `gorm:"foreignKey:PortalID" json:"portal,omitempty"`
 	Category           *Category `gorm:"foreignKey:CategoryID" json:"category,omitempty"`

backend/internal/repository/article_embedding_repo.go

@@ -65,7 +65,10 @@ func (r *ArticleEmbeddingRepo) SearchByEmbedding(ctx context.Context, portalID u
 		limit = 10
 	}
 
-	var articles []model.Article
+	var rows []struct {
+		model.Article
+		Distance *float64 `gorm:"column:semantic_distance"`
+	}
 	// Join articles with article_embeddings, compute cosine distance on vector_embedding column.
 	// pgvector cosine distance operator: <=> (for vector type)
 	err := r.db.WithContext(ctx).Raw(`
@@ -75,9 +78,14 @@ func (r *ArticleEmbeddingRepo) SearchByEmbedding(ctx context.Context, portalID u
 			AND a.deleted_at IS NULL AND ae.deleted_at IS NULL
 		ORDER BY semantic_distance
 		LIMIT ?
-	`, embedding, portalID, limit).Scan(&articles).Error
+	`, embedding, portalID, limit).Scan(&rows).Error
 	if err != nil {
 		return nil, err
 	}
+	articles := make([]model.Article, len(rows))
+	for i := range rows {
+		articles[i] = rows[i].Article
+		articles[i].SemanticDistance = rows[i].Distance
+	}
 	return articles, nil
 }

backend/internal/repository/article_embedding_repo_test.go

@@ -139,6 +139,7 @@ func TestArticleEmbeddingRepo_SearchByEmbedding_ExcludesSoftDeletedArticleAndEmb
 	before, err := repo.SearchByEmbedding(context.Background(), portal.ID, embedding, 10)
 	require.NoError(t, err)
 	require.Len(t, before, 3)
+	require.NotNil(t, before[0].SemanticDistance)
 	require.NoError(t, db.Delete(&articles[1]).Error)
 	require.NoError(t, repo.DeleteByArticleID(context.Background(), articles[2].ID))