Backup databases before migrating

database.go

@@ -9,6 +9,7 @@ import (
 // Db holds a connection to a SQLite database.
 type Db struct {
 	Db     *sqlite.Conn
+	source string
 	lock   sync.Mutex
 }
 
@@ -21,7 +22,7 @@ func OpenDb(databaseSource string) (*Db, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &Db{Db: conn}, nil
+	return &Db{Db: conn, source: databaseSource}, nil
 }
 
 // Close closes the database.

migrator.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io/fs"
 	"log"
+	"os"
 	"path"
 	"strconv"
 	"strings"
@@ -40,6 +41,20 @@ func (d *Db) MigrateDb(filesystem ReadDirFileFS, directory string) error {
 	}
 	log.Printf("Current version is %d, max migration version is %d", currentVersion, latestVersion)
 
+	// Create a backup if we're not on the latest version
+	if currentVersion != latestVersion && d.source != ":memory:" {
+		target := d.source + ".backup." + strconv.Itoa(currentVersion)
+		log.Printf("Creating backup of database to %s", target)
+		data, err := d.Db.Serialize("main")
+		if err != nil {
+			return fmt.Errorf("error serializing database: %v", err)
+		}
+		err = os.WriteFile(target, data, 0644)
+		if err != nil {
+			return fmt.Errorf("error writing backup: %v", err)
+		}
+	}
+
 	// If we are no up-to-date, bring the db up-to-date
 	for currentVersion != latestVersion {
 		targetVersion := currentVersion + 1

query.go

@@ -173,12 +173,23 @@ func (r *Rows) MustNext() bool {
 
 func (r *Rows) Scan(results ...any) error {
 	for i, arg := range results {
+		err := r.scanArgument(i, arg)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (r *Rows) scanArgument(i int, arg any) error {
 	if asString, ok := arg.(*string); ok {
 		*asString = r.query.stmt.ColumnText(i)
 	} else if asInt, ok := arg.(*int); ok {
 		*asInt = r.query.stmt.ColumnInt(i)
 	} else if asBool, ok := arg.(*bool); ok {
 		*asBool = r.query.stmt.ColumnBool(i)
+	} else if reflect.TypeOf(arg).Kind() == reflect.Ptr && reflect.TypeOf(arg).Elem().Kind() == reflect.Ptr {
+		return r.handleNullableType(i, arg)
 	} else {
 		if reflect.TypeOf(arg).Kind() != reflect.Ptr {
 			return fmt.Errorf("unsupported column type %s at index %d (it should be a pointer)", reflect.TypeOf(arg).Name(), i)
@@ -186,6 +197,19 @@ func (r *Rows) Scan(results ...any) error {
 		name := reflect.Indirect(reflect.ValueOf(arg)).Type().Name()
 		return fmt.Errorf("unsupported column type *%s at index %d", name, i)
 	}
+	return nil
+}
+
+func (r *Rows) handleNullableType(i int, asPtr any) error {
+	if r.query.stmt.ColumnIsNull(i) {
+		reflect.ValueOf(asPtr).Elem().Set(reflect.Zero(reflect.TypeOf(asPtr).Elem()))
+	} else {
+		value := reflect.New(reflect.TypeOf(asPtr).Elem().Elem()).Interface()
+		err := r.scanArgument(i, value)
+		if err != nil {
+			return err
+		}
+		reflect.ValueOf(asPtr).Elem().Set(reflect.ValueOf(value))
 	}
 	return nil
 }

query_test.go

@@ -90,3 +90,46 @@ func TestUpdateQueryWithWrongArguments(t *testing.T) {
 	err := db.Query("insert into mytable(key, value) values ('lorem', ?)").Bind(&value).Exec()
 	require.Error(t, err)
 }
+
+func TestQueryWithPointerStringArguments(t *testing.T) {
+	db := openTestDb(t)
+	var result *string
+	err := db.Query("select value from mytable where key = 'foo'").ScanSingle(&result)
+	require.NoError(t, err)
+	require.NotNil(t, result)
+	require.Equal(t, "bar", *result)
+}
+
+func TestQueryWithPointerStringArgumentsCanSetToNull(t *testing.T) {
+	db := openTestDb(t)
+	db.Query("update mytable set value=NULL where key = 'foo'").MustExec()
+	myString := "some string"
+	var result *string
+	result = &myString
+	err := db.Query("select value from mytable where key = 'foo'").ScanSingle(&result)
+	require.NoError(t, err)
+	require.Nil(t, result)
+}
+
+func TestDeleteQuery(t *testing.T) {
+	db := openTestDb(t)
+	db.Query("delete from mytable where key = 'foo'").MustExec()
+
+	var count int
+	db.Query("select count(*) from mytable where key = 'foo'").MustScanSingle(&count)
+	require.Equal(t, 0, count, "expected row to be deleted")
+}
+
+func TestTransactionRollback(t *testing.T) {
+	db := openTestDb(t)
+	func() {
+		tx := db.MustBegin()
+		defer tx.MustRollback()
+		tx.Query("update mytable set value = 'ipsum' where key = 'foo'").MustExec()
+		// Intentionally not committing the transaction
+	}()
+
+	var value string
+	db.Query("select value from mytable where key = 'foo'").MustScanSingle(&value)
+	require.Equal(t, "bar", value, "expected original value after rollback")
+}