Implement rollback command

commands.go

@@ -107,6 +107,29 @@ func doTransaction(db *sql.DB, txFunc func(shared.Transaction) error) error {
 	return tx.Commit()
 }
 
+func openDatabaseForMigration(ctx *cli.Context) (driver.Driver, *sql.DB, error) {
+	u, err := GetDatabaseURL(ctx)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	drv, err := driver.Get(u.Scheme)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	db, err := drv.Open(u)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	if err := drv.CreateMigrationsTable(db); err != nil {
+		return nil, nil, err
+	}
+
+	return drv, db, nil
+}
+
 // MigrateCommand migrates database to the latest version
 func MigrateCommand(ctx *cli.Context) error {
 	migrationsDir := ctx.GlobalString("migrations-dir")
@@ -119,27 +142,15 @@ func MigrateCommand(ctx *cli.Context) error {
 		return fmt.Errorf("No migration files found.")
 	}
 
-	u, err := GetDatabaseURL(ctx)
+	drv, db, err := openDatabaseForMigration(ctx)
+	if db != nil {
+		defer db.Close()
+	}
 	if err != nil {
 		return err
 	}
 
-	drv, err := driver.Get(u.Scheme)
-	if err != nil {
-		return err
-	}
-
-	db, err := drv.Open(u)
-	if err != nil {
-		return err
-	}
-	defer db.Close()
-
-	if err := drv.CreateMigrationsTable(db); err != nil {
-		return err
-	}
-
-	applied, err := drv.SelectMigrations(db)
+	applied, err := drv.SelectMigrations(db, -1)
 	if err != nil {
 		return err
 	}
@@ -178,31 +189,66 @@ func MigrateCommand(ctx *cli.Context) error {
 	return nil
 }
 
-func findAvailableMigrations(dir string) (map[string]struct{}, error) {
+func findMigrationFiles(dir string, re *regexp.Regexp) ([]string, error) {
 	files, err := ioutil.ReadDir(dir)
 	if err != nil {
 		return nil, fmt.Errorf("Could not find migrations directory `%s`.", dir)
 	}
 
-	nameRegexp := regexp.MustCompile(`^\d.*\.sql$`)
-	migrations := map[string]struct{}{}
-
+	matches := []string{}
 	for _, file := range files {
 		if file.IsDir() {
 			continue
 		}
 
 		name := file.Name()
-		if !nameRegexp.MatchString(name) {
+		if !re.MatchString(name) {
 			continue
 		}
 
+		matches = append(matches, name)
+	}
+
+	return matches, nil
+}
+
+func findAvailableMigrations(dir string) (map[string]struct{}, error) {
+	re := regexp.MustCompile(`^\d.*\.sql$`)
+	files, err := findMigrationFiles(dir, re)
+	if err != nil {
+		return nil, err
+	}
+
+	// why does go not have Set?
+	// convert into map for easier lookups
+	migrations := map[string]struct{}{}
+	for _, name := range files {
 		migrations[name] = struct{}{}
 	}
 
 	return migrations, nil
 }
 
+func findMigrationFile(dir string, ver string) (string, error) {
+	if ver == "" {
+		panic("migration version is required")
+	}
+
+	ver = regexp.QuoteMeta(ver)
+	re := regexp.MustCompile(fmt.Sprintf(`^%s.*\.sql$`, ver))
+
+	files, err := findMigrationFiles(dir, re)
+	if err != nil {
+		return "", err
+	}
+
+	if len(files) == 0 {
+		return "", fmt.Errorf("Can't find migration file: %s*.sql", ver)
+	}
+
+	return files[0], nil
+}
+
 func migrationVersion(filename string) string {
 	return regexp.MustCompile(`^\d+`).FindString(filename)
 }
@@ -243,3 +289,58 @@ func parseMigration(path string) (map[string]string, error) {
 
 	return migrations, nil
 }
+
+// RollbackCommand rolls back the most recent migration
+func RollbackCommand(ctx *cli.Context) error {
+	drv, db, err := openDatabaseForMigration(ctx)
+	if db != nil {
+		defer db.Close()
+	}
+	if err != nil {
+		return err
+	}
+
+	applied, err := drv.SelectMigrations(db, 1)
+	if err != nil {
+		return err
+	}
+
+	// grab most recent applied migration (applied has len=1)
+	latest := ""
+	for ver := range applied {
+		latest = ver
+	}
+	if latest == "" {
+		return fmt.Errorf("Can't rollback: no migrations have been applied.")
+	}
+
+	migrationsDir := ctx.GlobalString("migrations-dir")
+	filename, err := findMigrationFile(migrationsDir, latest)
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("Rolling back: %s\n", filename)
+
+	migration, err := parseMigration(filepath.Join(migrationsDir, filename))
+	if err != nil {
+		return err
+	}
+
+	// begin transaction
+	doTransaction(db, func(tx shared.Transaction) error {
+		// rollback migration
+		if _, err := tx.Exec(migration["down"]); err != nil {
+			return err
+		}
+
+		// remove migration record
+		if err := drv.DeleteMigration(tx, latest); err != nil {
+			return err
+		}
+
+		return nil
+	})
+
+	return nil
+}

driver/driver.go

@@ -14,7 +14,7 @@ type Driver interface {
 	CreateDatabase(*url.URL) error
 	DropDatabase(*url.URL) error
 	CreateMigrationsTable(*sql.DB) error
-	SelectMigrations(*sql.DB) (map[string]struct{}, error)
+	SelectMigrations(*sql.DB, int) (map[string]struct{}, error)
 	InsertMigration(shared.Transaction, string) error
 	DeleteMigration(shared.Transaction, string) error
 }

driver/postgres/postgres.go

@@ -67,8 +67,13 @@ func (postgres Driver) CreateMigrationsTable(db *sql.DB) error {
 }
 
 // SelectMigrations returns a list of applied migrations
-func (postgres Driver) SelectMigrations(db *sql.DB) (map[string]struct{}, error) {
-	rows, err := db.Query("SELECT version FROM schema_migrations")
+// with an optional limit (in descending order)
+func (postgres Driver) SelectMigrations(db *sql.DB, limit int) (map[string]struct{}, error) {
+	query := "SELECT version FROM schema_migrations ORDER BY version DESC"
+	if limit >= 0 {
+		query = fmt.Sprintf("%s LIMIT %d", query, limit)
+	}
+	rows, err := db.Query(query)
 	if err != nil {
 		return nil, err
 	}

main.go

@@ -42,6 +42,13 @@ func NewApp() *cli.App {
 				runCommand(MigrateCommand, ctx)
 			},
 		},
+		{
+			Name:  "rollback",
+			Usage: "Rollback the most recent migration",
+			Action: func(ctx *cli.Context) {
+				runCommand(RollbackCommand, ctx)
+			},
+		},
 		{
 			Name:  "new",
 			Usage: "Generate a new migration file",