improve test coverage, error reporting for Select()

1 files changed, 68 insertions, 0 deletions

diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..1e81060
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,68 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package oblast
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+// MissingRecordError is returned by [Store.Update] if one of the rows to be updated does not exist in the DB.
+type MissingRecordError[R any] struct {
+	// The record that was provided to [Store.Update],
+	// but for which no row with the same primary key values could be located.
+	Record R
+	plan   plan
+}
+
+// Error implements the builtin/error interface.
+func (e MissingRecordError[R]) Error() string {
+	keyDescs := make([]string, len(e.plan.PrimaryKeyColumnNames))
+	v := reflect.ValueOf(e.Record)
+	for idx, columnName := range e.plan.PrimaryKeyColumnNames {
+		keyDescs[idx] = fmt.Sprintf("%s = %#v", columnName, v.FieldByIndex(e.plan.IndexByColumnName[columnName]))
+	}
+	return "could not UPDATE record that does not exist in the database: " + strings.Join(keyDescs, ", ")
+}
+
+// An error type that optionally contains either one of the following or both:
+// - a core error from an IO operation (e.g. a database read)
+// - an auxiliary error from closing or otherwise cleaning up the respective IO handle
+type ioError struct {
+	MainError        error
+	CleanupError     error
+	CleanupOperation string
+}
+
+func newIOError(err error, cleanupOperation string, cleanupErr error) error {
+	if err == nil && cleanupErr == nil {
+		return nil
+	}
+	return ioError{err, cleanupErr, cleanupOperation}
+}
+
+// Error implements the builtin/error interface.
+func (e ioError) Error() string {
+	switch {
+	case e.CleanupError == nil:
+		return e.MainError.Error()
+	case e.MainError == nil:
+		return fmt.Sprintf("during %s(): %s", e.CleanupOperation, e.CleanupError.Error())
+	default:
+		return fmt.Sprintf("%s (additional error during %s(): %s)", e.MainError.Error(), e.CleanupOperation, e.CleanupError.Error())
+	}
+}
+
+// Unwrap implements the interface implied by the documentation of package errors.
+func (e ioError) Unwrap() []error {
+	result := make([]error, 0, 2)
+	if e.MainError != nil {
+		result = append(result, e.MainError)
+	}
+	if e.CleanupError != nil {
+		result = append(result, e.CleanupError)
+	}
+	return result
+}