backend: Add migration down support

backend/cmd/initdb/initdb.go

@@ -7,7 +7,7 @@ import (
 )
 
 func main() {
-	if _, err := api.New(api.OptionInitDB); err != nil {
+	if _, err := api.NewWithMigrations(api.OptionInitDB); err != nil {
 		log.Fatal(err)
 	}
 }

backend/cmd/nebraska/main.go

@@ -26,8 +26,22 @@ func main() {
 		log.Fatalf("Config is invaliad, err: %w\n", err)
 	}
 
+	if conf.RollbackDBTo != "" {
+		db, err := db.New()
+		if err != nil {
+			log.Fatal("DB connection err:", err)
+		}
+
+		count, err := db.MigrateDown(conf.RollbackDBTo)
+		if err != nil {
+			log.Fatal("DB migration down err:", err)
+		}
+		log.Infof("DB migration down successful, migrated %d levels down", count)
+		return
+	}
+
 	// create new DB
-	db, err := db.New()
+	db, err := db.NewWithMigrations()
 	if err != nil {
 		log.Fatal("DB connection err:", err)
 	}

backend/pkg/api/api.go

@@ -1,10 +1,14 @@
 package api
 
 import (
+	"database/sql"
 	"errors"
+	"fmt"
 	"os"
+	"strconv"
 
 	//register "pgx" sql driver
+	"github.com/doug-martin/goqu/v9"
 	_ "github.com/jackc/pgx/v4/stdlib"
 	"github.com/jmoiron/sqlx"
 	migrate "github.com/rubenv/sql-migrate"
@@ -14,7 +18,6 @@ import (
 	// Postgresql driver
 	_ "github.com/lib/pq"
 
-	"strconv"
 	"time"
 )
 
@@ -55,6 +58,8 @@ var (
 	ErrArchMismatch = errors.New("nebraska: mismatched arches")
 )
 
+const migrationsTable = "database_migrations"
+
 // API represents an api instance used to interact with Nebraska entities.
 type API struct {
 	db       *sqlx.DB
@@ -66,8 +71,7 @@ type API struct {
 	disableUpdatesOnFailedRollout bool
 }
 
-// New creates a new API instance, creating the underlying db connection and
-// applying db migrations available.
+// New creates a new API instance, creates the underlying db connection.
 func New(options ...func(*API) error) (*API, error) {
 	api := &API{
 		dbDriver: "pgx",
@@ -117,13 +121,20 @@ func New(options ...func(*API) error) (*API, error) {
 			return nil, err
 		}
 	}
+	return api, nil
+}
 
-	migrate.SetTable("database_migrations")
-	migrations := &migrate.AssetMigrationSource{
-		Asset:    Asset,
-		AssetDir: AssetDir,
-		Dir:      "db/migrations",
+// NewWithMigrations creates a new API instance, creates the underlying db connection and
+// applies all available db migrations.
+func NewWithMigrations(options ...func(*API) error) (*API, error) {
+	api, err := New(options...)
+	if err != nil {
+		return nil, err
 	}
+
+	migrate.SetTable(migrationsTable)
+	migrations := migrationAssets()
+
 	if _, err := migrate.Exec(api.db.DB, "postgres", migrations, migrate.Up); err != nil {
 		return nil, err
 	}
@@ -133,6 +144,62 @@ func New(options ...func(*API) error) (*API, error) {
 	return api, nil
 }
 
+type migration struct {
+	ID        string    `db:"id"`
+	AppliedAt time.Time `db:"applied_at"`
+}
+
+func (api *API) MigrateDown(version string) (int, error) {
+
+	migrate.SetTable(migrationsTable)
+	migrations := migrationAssets()
+
+	// find version based on input string
+	query, _, err := goqu.Select("*").From(migrationsTable).Where(goqu.C("id").Like(fmt.Sprintf("%s%%", version))).ToSQL()
+	if err != nil {
+		return 0, err
+	}
+
+	var mig migration
+	err = api.db.QueryRowx(query).StructScan(&mig)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return 0, fmt.Errorf("no migrations found for: %s, err: %v", version, err)
+		}
+		return 0, err
+	}
+
+	// find  count of migrations that have been applied after the version
+	query, _, err = goqu.Select(goqu.COUNT("*")).From(migrationsTable).Where(goqu.C("applied_at").Gt(mig.AppliedAt)).ToSQL()
+	if err != nil {
+		return 0, err
+	}
+
+	countMap := make(map[string]interface{})
+
+	err = api.db.QueryRowx(query).MapScan(countMap)
+	if err != nil {
+		return 0, err
+	}
+
+	levels := countMap["count"].(int64)
+	logger.Info().Msgf("migrating down %d levels", levels)
+	count, err := migrate.ExecMax(api.db.DB, "postgres", migrations, migrate.Down, int(levels))
+	if err != nil {
+		return 0, err
+	}
+	logger.Info().Msg("successfully migrated down")
+	return count, nil
+}
+
+func migrationAssets() *migrate.AssetMigrationSource {
+	return &migrate.AssetMigrationSource{
+		Asset:    Asset,
+		AssetDir: AssetDir,
+		Dir:      "db/migrations",
+	}
+}
+
 // OptionInitDB will initialize the database during the API instance creation,
 // dropping all existing tables, which will force all migration scripts to be
 // re-executed. Use with caution, this will DESTROY ALL YOUR DATA.
@@ -166,7 +233,7 @@ func (api *API) Close() {
 // NewForTest creates a new API instance with given options and fills
 // the database with sample data for testing purposes.
 func NewForTest(options ...func(*API) error) (*API, error) {
-	a, err := New(options...)
+	a, err := NewWithMigrations(options...)
 	if err != nil {
 		return nil, err
 	}

backend/pkg/api/api_test.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"testing"
 
+	"github.com/doug-martin/goqu/v9"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -31,7 +33,7 @@ func TestMain(m *testing.M) {
 		_ = os.Setenv("NEBRASKA_DB_URL", defaultTestDbURL)
 	}
 
-	a, err := New(OptionInitDB)
+	a, err := NewWithMigrations(OptionInitDB)
 	if err != nil {
 		log.Printf("Failed to init DB: %v\n", err)
 		log.Println("These tests require PostgreSQL running and a tests database created, please adjust NEBRASKA_DB_URL as needed.")
@@ -41,3 +43,31 @@ func TestMain(m *testing.M) {
 
 	os.Exit(m.Run())
 }
+
+func TestMigrateDown(t *testing.T) {
+
+	// Create New DB
+	db, err := NewWithMigrations(OptionInitDB)
+	require.NoError(t, err)
+	defer db.Close()
+
+	_, err = db.MigrateDown("0004")
+	require.NoError(t, err)
+
+	query, _, err := goqu.Select("*").From(migrationsTable).ToSQL()
+	require.NoError(t, err)
+
+	var migrations []migration
+	rows, err := db.db.Queryx(query)
+	require.NoError(t, err)
+
+	defer rows.Close()
+	for rows.Next() {
+		var mig migration
+		err := rows.StructScan(&mig)
+		require.NoError(t, err)
+		migrations = append(migrations, mig)
+	}
+
+	assert.Equal(t, 4, len(migrations))
+}