migrations: capture next/previous versions - can't assume migration IDs will be sequential

README.md

@@ -74,4 +74,4 @@ A sample dbconf.yml looks like
 
 Here, `development` specifies the name of the configuration, and the `driver` and `open` elements are passed directly to database/sql to access the specified database.
 
-You may include as many configurations as you like, and you can use the `--config` command line option to specify which one to use. goose defaults to using a configuration called `development`.
+You may include as many configurations as you like, and you can use the `--config` command line option to specify which one to use. goose defaults to using a configuration called `development`.

cmd/goose.go

@@ -27,10 +27,16 @@ type DBVersion struct {
 	TStamp    time.Time
 }
 
+type Migration struct {
+	Next     int    // next version, or -1 if none
+	Previous int    // previous version, -1 if none
+	Source   string // .go or .sql script
+}
+
 type MigrationMap struct {
-	Versions  []int          // sorted slice of version keys
-	Sources   map[int]string // sources (.sql or .go) keyed by version
-	Direction bool           // sort direction: true -> Up, false -> Down
+	Versions   []int             // sorted slice of version keys
+	Migrations map[int]Migration // sources (.sql or .go) keyed by version
+	Direction  bool              // sort direction: true -> Up, false -> Down
 }
 
 var dbFolder = flag.String("db", "db", "folder containing db info")
@@ -53,7 +59,7 @@ func dbConfFromFile(path, envtype string) (*DBConf, error) {
 
 	f, err := yaml.ReadFile(path)
 	if err != nil {
-		log.Fatal(err)
+		return nil, err
 	}
 
 	drv, derr := f.Get(fmt.Sprintf("%s.driver", envtype))
@@ -85,12 +91,12 @@ func runMigrations(conf *DBConf, target int) {
 		log.Fatal("couldn't get/set DB version")
 	}
 
-	migrations, err := collectMigrations(path.Join(*dbFolder, "migrations"), currentVersion)
+	mm, err := collectMigrations(path.Join(*dbFolder, "migrations"), currentVersion)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	if len(migrations.Versions) == 0 {
+	if len(mm.Versions) == 0 {
 		fmt.Printf("goose: no migrations to run. current version: %d\n", currentVersion)
 		return
 	}
@@ -98,18 +104,18 @@ func runMigrations(conf *DBConf, target int) {
 	fmt.Printf("goose: migrating db configuration '%v', current version: %d, target: %d\n",
 		conf.Name, currentVersion, *targetVersion)
 
-	for _, v := range migrations.Versions {
+	for _, v := range mm.Versions {
 
 		var numStatements int
 		var e error
 
-		filepath := migrations.Sources[v]
+		filepath := mm.Migrations[v].Source
 
 		switch path.Ext(filepath) {
 		case ".go":
-			numStatements, e = runGoMigration(conf, filepath, v, migrations.Direction)
+			numStatements, e = runGoMigration(conf, filepath, v, mm.Direction)
 		case ".sql":
-			numStatements, e = runSQLMigration(db, filepath, v, migrations.Direction)
+			numStatements, e = runSQLMigration(db, filepath, v, mm.Direction)
 		}
 
 		if e != nil {
@@ -135,7 +141,7 @@ func collectMigrations(dirpath string, currentVersion int) (mm *MigrationMap, er
 	}
 
 	mm = &MigrationMap{
-		Sources: make(map[int]string),
+		Migrations: make(map[int]Migration),
 	}
 
 	// extract the numeric component of each migration,
@@ -153,7 +159,7 @@ func collectMigrations(dirpath string, currentVersion int) (mm *MigrationMap, er
 			continue
 		}
 
-		if _, ok := mm.Sources[v]; ok {
+		if _, ok := mm.Migrations[v]; ok {
 			log.Fatalf("more than one file specifies the migration for version %d (%s and %s)",
 				v, mm.Versions[v], path.Join(dirpath, name))
 		}
@@ -190,7 +196,11 @@ func versionFilter(v, current, target int) bool {
 
 func (m *MigrationMap) Append(v int, source string) {
 	m.Versions = append(m.Versions, v)
-	m.Sources[v] = source
+	m.Migrations[v] = Migration{
+		Next:     -1,
+		Previous: -1,
+		Source:   source,
+	}
 }
 
 func (m *MigrationMap) Sort(currentVersion int) {
@@ -208,6 +218,24 @@ func (m *MigrationMap) Sort(currentVersion int) {
 			m.Versions[i], m.Versions[j] = m.Versions[j], m.Versions[i]
 		}
 	}
+
+	// now that we're sorted in the appropriate direction,
+	// populate next and previous for each migration
+	//
+	// work around http://code.google.com/p/go/issues/detail?id=3117
+	previousV := -1
+	for _, v := range m.Versions {
+		cur := m.Migrations[v]
+		cur.Previous = previousV
+
+		// if a migration exists at prev, its next is now v
+		if prev, ok := m.Migrations[previousV]; ok {
+			prev.Next = v
+			m.Migrations[previousV] = prev
+		}
+
+		previousV = v
+	}
 }
 
 // look for migration scripts with names in the form:
@@ -247,7 +275,7 @@ func ensureDBVersion(db *sql.DB) (int, error) {
               );`
 	insert := "INSERT INTO goose_db_version (version_id) VALUES (0);"
 
-	for _, str := range [2]string{create, insert} {
+	for _, str := range []string{create, insert} {
 		if _, err := txn.Exec(str); err != nil {
 			txn.Rollback()
 			return 0, err