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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"
)
// Select executes the provided SQL query and fills an instance of the record type R for each row in the result set,
// according to the column names reported by the database as part of the result set.
//
// An error is returned if any column name in the result set does not correspond to an addressable field in R.
func (s Store[R]) Select(db Handle, query string, args ...any) (result []R, returnedError error) {
// NOTE: This function body should be as short as possible to reduce the binary size after monomorphization.
// Any expression that does not depend on type R should be factored out into a reusable function.
rows, indexes, err := startQuery(db, s.plan, query, args...)
if err != nil {
return nil, err
}
defer func() {
returnedError = mergeRowsCloseError(returnedError, rows.Close())
}()
slots := make([]any, len(indexes))
for rows.Next() {
var target R
err = collectRow(rows, reflect.ValueOf(&target).Elem(), slots, indexes)
if err != nil {
return nil, err
}
result = append(result, target)
}
return result, nil
}
func startQuery(db Handle, 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, fmt.Errorf("during Query(): %w", 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, fmt.Errorf("during rows.Columns(): %w", 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
}
func collectRow(rows *sql.Rows, v reflect.Value, slots []any, indexes [][]int) error {
for idx, index := range indexes {
slots[idx] = v.FieldByIndex(index).Addr().Interface()
}
err := rows.Scan(slots...)
if err != nil {
return fmt.Errorf("during rows.Scan(): %w", err)
}
return nil
}
func mergeRowsCloseError(err, closeErr error) error {
switch {
case closeErr == nil:
return err
case err == nil:
return fmt.Errorf("during rows.Close(): %w", closeErr)
default:
return fmt.Errorf("%w (additional error during rows.Close(): %s)", err, closeErr.Error())
}
}
// SelectOne executes the provided SQL query and fills an instance of the record type R if there is exactly one row in the result set,
// according to the column names reported by the database as part of the result set.
//
// If there are no rows in the result set, [sql.ErrNoRows] is returned.
// If there are multiple rows in the result set, [ErrMultipleRows] is returned.
//
// Warning: Because of limitations in the interface of database/sql, this function is built on [Store.Select] and cannot be any faster than it.
// For maximum performance, use [Store.SelectOneWhere] which avoids the overhead of potentially having to read multiple rows.
func (s Store[R]) SelectOne(db Handle, query string, args ...any) (result R, err error) {
// NOTE: This function body should be as short as possible to reduce the binary size after monomorphization.
// Any expression that does not depend on type R should be factored out into a reusable function.
var results []R
results, err = s.Select(db, query, args...)
if err == nil {
switch len(results) {
case 0:
err = sql.ErrNoRows
case 1:
result = results[0]
default:
err = ErrMultipleRows
}
}
return
}
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