Revert "remove FetchOne helpers"

This reverts commit 88755830e5.

dbx.go

@@ -60,6 +60,12 @@ type Statement interface {
 	ExecContext(ctx context.Context, db qrm.Executable) (sql.Result, error)
 }
 
+// SelectStatement is a Jet statement that can be executed to fetch rows from the database.
+type SelectStatement interface {
+	Statement
+	LIMIT(limit int64) SelectStatement
+}
+
 var (
 	// ErrNoRows is returned when a query returns no rows.
 	ErrNoRows = qrm.ErrNoRows
@@ -108,7 +114,7 @@ func ModuleDB(dialect Dialect, cfg *DBConfig, forceDebugLog bool) *app.Module {
 
 // Fetch queries the database and returns the result as a slice. If the query
 // returns no rows, it returns an empty slice and no error.
-func Fetch[T any](sqlo Queryable, stmt Statement) ([]*T, error) {
+func Fetch[T any](sqlo Queryable, stmt SelectStatement) ([]*T, error) {
 	var result []*T
 	if err := stmt.Query(sqlo, &result); err != nil && !errors.Is(err, ErrNoRows) {
 		return nil, err
@@ -118,7 +124,7 @@ func Fetch[T any](sqlo Queryable, stmt Statement) ([]*T, error) {
 
 // MustFetch queries the database and returns the result as a slice. If the query
 // returns no rows, it returns an empty slice and the desired error.
-func MustFetch[T any](sqlo Queryable, stmt Statement, notFoundErr error) ([]*T, error) {
+func MustFetch[T any](sqlo Queryable, stmt SelectStatement, notFoundErr error) ([]*T, error) {
 	result, err := Fetch[T](sqlo, stmt)
 	if err != nil {
 		return nil, err
@@ -129,6 +135,29 @@ func MustFetch[T any](sqlo Queryable, stmt Statement, notFoundErr error) ([]*T,
 	return result, nil // return the fetched results
 }
 
+// FetchOne queries the database and returns a single result. If the query
+// returns no rows, it returns nil and no error.
+func FetchOne[T any](sqlo Queryable, stmt SelectStatement) (*T, error) {
+	result, err := Fetch[T](sqlo, stmt.LIMIT(1))
+	if err != nil {
+		return nil, err
+	}
+	if len(result) == 0 {
+		return nil, nil // no rows found, return nil
+	}
+	return result[0], nil // return the first (and only) result
+}
+
+// MustFetchOne queries the database and returns a single result. If the query
+// returns no rows, it returns nil and the desired error.
+func MustFetchOne[T any](sqlo Queryable, stmt SelectStatement, notFoundErr error) (*T, error) {
+	result, err := MustFetch[T](sqlo, stmt.LIMIT(1), notFoundErr)
+	if err != nil {
+		return nil, err
+	}
+	return result[0], nil // return the first (and only) result
+}
+
 // Insert executes an insert statement, returning the last inserted ID or an
 // error if the insert fails.
 func Insert(sqlo Executable, stmt Statement) (uint64, error) {