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// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
// SPDX-License-Identifier: Apache-2.0
package oblast
import (
"database/sql"
"fmt"
"reflect"
"go.xyrillian.de/oblast/internal"
)
func Select[T any](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, indexes, err := db.startQuery(plan, query, args...)
if err != nil {
return nil, err
}
defer rows.Close()
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
}
func (db *DB) startQuery(plan internal.Plan, query string, args ...any) (rows *sql.Rows, indexes [][]int, err error) {
rows, err = db.Query(query, args...)
if err != nil {
return nil, nil, err
}
defer func() {
if err != nil {
closeErr := rows.Close()
if closeErr != nil {
err = fmt.Errorf("%w (additional error during rows.Close: %s)", err, closeErr.Error())
}
}
}()
columnNames, err := rows.Columns()
if err != nil {
return nil, nil, err
}
indexes = make([][]int, len(columnNames))
for idx, columnName := range columnNames {
var ok bool
indexes[idx], ok = plan.IndexByColumnName[columnName]
if !ok {
return nil, nil, fmt.Errorf(
"result has column %q in position %d, but no field in record type has `db:%[1]q`",
columnName, idx,
)
}
}
return rows, indexes, nil
}
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