fix: properly handle NULL UserName in database operations

Add scanSignature helper to convert sql.NullString to string type.
Update Create method to insert NULL for empty UserName values.
Fix integration tests to work with string type instead of pointer.

Author: btouchard

internal/infrastructure/database/repository.go

@@ -18,19 +18,56 @@ func NewSignatureRepository(db *sql.DB) *SignatureRepository {
 	return &SignatureRepository{db: db}
 }
 
+// scanSignature scans a row into a Signature, handling NULL values properly
+func scanSignature(scanner interface {
+	Scan(dest ...interface{}) error
+}, signature *models.Signature) error {
+	var userName sql.NullString
+	err := scanner.Scan(
+		&signature.ID,
+		&signature.DocID,
+		&signature.UserSub,
+		&signature.UserEmail,
+		&userName,
+		&signature.SignedAtUTC,
+		&signature.PayloadHash,
+		&signature.Signature,
+		&signature.Nonce,
+		&signature.CreatedAt,
+		&signature.Referer,
+		&signature.PrevHash,
+	)
+	if err != nil {
+		return err
+	}
+	// Convert sql.NullString to string (empty string if NULL)
+	if userName.Valid {
+		signature.UserName = userName.String
+	} else {
+		signature.UserName = ""
+	}
+	return nil
+}
+
 func (r *SignatureRepository) Create(ctx context.Context, signature *models.Signature) error {
 	query := `
 		INSERT INTO signatures (doc_id, user_sub, user_email, user_name, signed_at, payload_hash, signature, nonce, referer, prev_hash)
 		VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
 		RETURNING id, created_at
 	`
 
+	// Convert empty string to NULL for user_name
+	var userName sql.NullString
+	if signature.UserName != "" {
+		userName = sql.NullString{String: signature.UserName, Valid: true}
+	}
+
 	err := r.db.QueryRowContext(
 		ctx, query,
 		signature.DocID,
 		signature.UserSub,
 		signature.UserEmail,
-		signature.UserName,
+		userName,
 		signature.SignedAtUTC,
 		signature.PayloadHash,
 		signature.Signature,
@@ -49,25 +86,12 @@ func (r *SignatureRepository) Create(ctx context.Context, signature *models.Sign
 func (r *SignatureRepository) GetByDocAndUser(ctx context.Context, docID, userSub string) (*models.Signature, error) {
 	query := `
 		SELECT id, doc_id, user_sub, user_email, user_name, signed_at, payload_hash, signature, nonce, created_at, referer, prev_hash
-		FROM signatures 
+		FROM signatures
 		WHERE doc_id = $1 AND user_sub = $2
 	`
 
 	signature := &models.Signature{}
-	err := r.db.QueryRowContext(ctx, query, docID, userSub).Scan(
-		&signature.ID,
-		&signature.DocID,
-		&signature.UserSub,
-		&signature.UserEmail,
-		&signature.UserName,
-		&signature.SignedAtUTC,
-		&signature.PayloadHash,
-		&signature.Signature,
-		&signature.Nonce,
-		&signature.CreatedAt,
-		&signature.Referer,
-		&signature.PrevHash,
-	)
+	err := scanSignature(r.db.QueryRowContext(ctx, query, docID, userSub), signature)
 
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
@@ -98,21 +122,7 @@ func (r *SignatureRepository) GetByDoc(ctx context.Context, docID string) ([]*mo
 	var signatures []*models.Signature
 	for rows.Next() {
 		signature := &models.Signature{}
-		err := rows.Scan(
-			&signature.ID,
-			&signature.DocID,
-			&signature.UserSub,
-			&signature.UserEmail,
-			&signature.UserName,
-			&signature.SignedAtUTC,
-			&signature.PayloadHash,
-			&signature.Signature,
-			&signature.Nonce,
-			&signature.CreatedAt,
-			&signature.Referer,
-			&signature.PrevHash,
-		)
-		if err != nil {
+		if err := scanSignature(rows, signature); err != nil {
 			continue
 		}
 		signatures = append(signatures, signature)
@@ -140,21 +150,7 @@ func (r *SignatureRepository) GetByUser(ctx context.Context, userSub string) ([]
 	var signatures []*models.Signature
 	for rows.Next() {
 		signature := &models.Signature{}
-		err := rows.Scan(
-			&signature.ID,
-			&signature.DocID,
-			&signature.UserSub,
-			&signature.UserEmail,
-			&signature.UserName,
-			&signature.SignedAtUTC,
-			&signature.PayloadHash,
-			&signature.Signature,
-			&signature.Nonce,
-			&signature.CreatedAt,
-			&signature.Referer,
-			&signature.PrevHash,
-		)
-		if err != nil {
+		if err := scanSignature(rows, signature); err != nil {
 			continue
 		}
 		signatures = append(signatures, signature)
@@ -195,26 +191,13 @@ func (r *SignatureRepository) CheckUserSignatureStatus(ctx context.Context, docI
 func (r *SignatureRepository) GetLastSignature(ctx context.Context) (*models.Signature, error) {
 	query := `
 		SELECT id, doc_id, user_sub, user_email, user_name, signed_at, payload_hash, signature, nonce, created_at, referer, prev_hash
-		FROM signatures 
-		ORDER BY id DESC 
+		FROM signatures
+		ORDER BY id DESC
 		LIMIT 1
 	`
 
 	signature := &models.Signature{}
-	err := r.db.QueryRowContext(ctx, query).Scan(
-		&signature.ID,
-		&signature.DocID,
-		&signature.UserSub,
-		&signature.UserEmail,
-		&signature.UserName,
-		&signature.SignedAtUTC,
-		&signature.PayloadHash,
-		&signature.Signature,
-		&signature.Nonce,
-		&signature.CreatedAt,
-		&signature.Referer,
-		&signature.PrevHash,
-	)
+	err := scanSignature(r.db.QueryRowContext(ctx, query), signature)
 
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
@@ -243,21 +226,7 @@ func (r *SignatureRepository) GetAllSignaturesOrdered(ctx context.Context) ([]*m
 	var signatures []*models.Signature
 	for rows.Next() {
 		signature := &models.Signature{}
-		err := rows.Scan(
-			&signature.ID,
-			&signature.DocID,
-			&signature.UserSub,
-			&signature.UserEmail,
-			&signature.UserName,
-			&signature.SignedAtUTC,
-			&signature.PayloadHash,
-			&signature.Signature,
-			&signature.Nonce,
-			&signature.CreatedAt,
-			&signature.Referer,
-			&signature.PrevHash,
-		)
-		if err != nil {
+		if err := scanSignature(rows, signature); err != nil {
 			continue
 		}
 		signatures = append(signatures, signature)

internal/infrastructure/database/repository_constraints_test.go

@@ -62,7 +62,7 @@ func TestRepository_DatabaseConstraints_Integration(t *testing.T) {
 			{
 				name: "valid signature with nulls",
 				modifyFn: func(s *models.Signature) {
-					s.UserName = nil
+					s.UserName = ""
 					s.Referer = nil
 					s.PrevHash = nil
 				},
@@ -403,7 +403,7 @@ func TestRepository_EdgeCases_Integration(t *testing.T) {
 		// Test with empty strings for nullable fields
 		sig := factory.CreateValidSignature()
 		emptyString := ""
-		sig.UserName = &emptyString
+		sig.UserName = emptyString
 		sig.Referer = &emptyString
 		sig.PrevHash = &emptyString
 
@@ -418,7 +418,7 @@ func TestRepository_EdgeCases_Integration(t *testing.T) {
 		}
 
 		// Verify empty strings are preserved (not converted to NULL)
-		if result.UserName == nil || *result.UserName != "" {
+		if result.UserName != "" {
 			t.Error("Empty string UserName not preserved")
 		}
 		if result.Referer == nil || *result.Referer != "" {