move Select() to separate file

1 files changed, 58 insertions, 0 deletions

diff --git a/query.go b/query.go
new file mode 100644
index 0000000..94dc17b
--- /dev/null
+++ b/query.go
@@ -0,0 +1,58 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package oblast
+
+import (
+	"context"
+	"fmt"
+	"reflect"
+)
+
+func Select[T any](ctx context.Context, db *DB, query string, args ...any) ([]T, error) {
+	// TODO: minimize function body to avoid binary size blowup from monomorphization
+	// TODO: catch error from rows.Close(), if any
+	// TODO: add context to errors
+
+	plan, err := db.getPlan(reflect.TypeFor[T]())
+	if err != nil {
+		return nil, err
+	}
+	rows, err := db.Query(query, args...)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	columnNames, err := rows.Columns()
+	if err != nil {
+		return nil, err
+	}
+	indexes := make([][]int, len(columnNames))
+	for idx, columnName := range columnNames {
+		var ok bool
+		indexes[idx], ok = plan.IndexByColumnName[columnName]
+		if !ok {
+			var zero T
+			return nil, fmt.Errorf("result has column %q in position %d, but no field in %T has `db:%[1]q`",
+				columnName, idx, zero)
+		}
+	}
+
+	var result []T
+	slots := make([]any, len(indexes))
+	for rows.Next() {
+		var target T
+		rvalue := reflect.ValueOf(&target).Elem()
+		for idx, index := range indexes {
+			slots[idx] = rvalue.FieldByIndex(index).Addr().Interface()
+		}
+		err := rows.Scan(slots...)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, target)
+	}
+
+	return result, nil
+}