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introduce ScanWith to supply custom scanner funcs
Signed-off-by: oppiliappan <me@oppi.li>
+84
-7
+21
-7
scanner.go
+21
-7
scanner.go
···
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)
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type Scanner[T any] struct {
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rows *sql.Rows
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onError func(err error)
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rows *sql.Rows
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scanFunc func(*T) []any
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onError func(err error)
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}
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func NewScanner[T any](rows *sql.Rows) Scanner[T] {
···
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}
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}
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func (s *Scanner[T]) Scan() iter.Seq2[T, error] {
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return func(yield func(T, error) bool) {
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for s.rows.Next() {
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var data T
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elem := reflect.ValueOf(&data).Elem()
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func (s Scanner[T]) ScanWith(fn func(*T) []any) iter.Seq2[T, error] {
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s.scanFunc = fn
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return s.Scan()
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}
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func (s Scanner[T]) Scan() iter.Seq2[T, error] {
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// If no custom scan function provided, use reflection-based default
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if s.scanFunc == nil {
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s.scanFunc = func(dest *T) []any {
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elem := reflect.ValueOf(dest).Elem()
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numCols := elem.NumField()
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columns := make([]any, numCols)
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···
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columns[i] = field.Addr().Interface()
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}
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return columns
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}
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}
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return func(yield func(T, error) bool) {
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for s.rows.Next() {
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var data T
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columns := s.scanFunc(&data)
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err := s.rows.Scan(columns...)
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if !yield(data, err) {
+63
scanner_test.go
+63
scanner_test.go
···
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t.Errorf("user data incorrect: %+v", u)
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}
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}
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func TestScannerWithCustomMapping(t *testing.T) {
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db := setupTestDB(t)
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defer db.Close()
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rows, err := db.Query("SELECT email, name, id FROM users ORDER BY id")
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if err != nil {
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t.Fatalf("Failed to query users: %v", err)
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}
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scanner := NewScanner[UserBasic](rows)
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defer scanner.Close()
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var users []UserBasic
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for user, err := range scanner.ScanWith(func(dest *UserBasic) []any {
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return []any{&dest.Email, &dest.Name, &dest.ID}
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}) {
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if err != nil {
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t.Fatalf("Failed to scan user: %v", err)
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}
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users = append(users, user)
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}
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if len(users) != 6 {
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t.Errorf("Expected 6 users, got %d", len(users))
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}
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if users[0].ID != 1 || users[0].Name != "John Doe" || users[0].Email != "john@example.com" {
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t.Errorf("Expected first user to be John Doe, got %+v", users[0])
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}
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}
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func TestScannerWithSkipColumn(t *testing.T) {
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db := setupTestDB(t)
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defer db.Close()
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rows, err := db.Query("SELECT id, email, age, name FROM users ORDER BY id LIMIT 1")
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if err != nil {
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t.Fatalf("Failed to query users: %v", err)
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}
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scanner := NewScanner[UserBasic](rows)
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defer scanner.Close()
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var users []UserBasic
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for user, err := range scanner.ScanWith(func(dest *UserBasic) []any {
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var discard any
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return []any{&dest.ID, &dest.Email, &discard, &dest.Name}
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}) {
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if err != nil {
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t.Fatalf("Failed to scan user: %v", err)
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}
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users = append(users, user)
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}
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if len(users) != 1 {
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t.Errorf("Expected 1 user, got %d", len(users))
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}
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if users[0].ID != 1 || users[0].Name != "John Doe" || users[0].Email != "john@example.com" {
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t.Errorf("User data incorrect: %+v", users[0])
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}
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}