Backup databases before migrating

database.go

@@ -8,8 +8,9 @@ import (
 
 // Db holds a connection to a SQLite database.
 type Db struct {
-	Db   *sqlite.Conn
+	Db     *sqlite.Conn
-	lock sync.Mutex
+	source string
+	lock   sync.Mutex
 }
 
 // OpenDb opens a new connection to a SQLite database.
@@ -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_test.go

@@ -110,3 +110,26 @@ func TestQueryWithPointerStringArgumentsCanSetToNull(t *testing.T) {
 	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")
+}