Refactor migration.

Add `ChangeColumn`, `AddIndex`, `DropIndex` method to
Operation interface.

pkg/database/database.go

@@ -27,7 +27,7 @@ var db *sql.DB
 func Init(name, datasource string) error {
 	driver := map[string]struct {
 		Md *meddler.Database
-		Mg migrate.DriverFunction
+		Mg migrate.DriverBuilder
 	}{
 		"sqlite3": {
 			meddler.SQLite,

pkg/database/migrate/api.go

@@ -0,0 +1,36 @@
+package migrate
+
+import (
+	"database/sql"
+)
+
+// Operation interface covers basic migration operations.
+// Implementation details is specific for each database,
+// see migrate/sqlite.go for implementation reference.
+type Operation interface {
+	CreateTable(tableName string, args []string) (sql.Result, error)
+
+	RenameTable(tableName, newName string) (sql.Result, error)
+
+	DropTable(tableName string) (sql.Result, error)
+
+	AddColumn(tableName, columnSpec string) (sql.Result, error)
+
+	ChangeColumn(tableName, columnName, newType string) (sql.Result, error)
+
+	DropColumns(tableName string, columnsToDrop []string) (sql.Result, error)
+
+	RenameColumns(tableName string, columnChanges map[string]string) (sql.Result, error)
+
+	AddIndex(tableName string, columns []string, flag string) (sql.Result, error)
+
+	DropIndex(tableName string, columns[]string) (sql.Result, error)
+}
+
+type MigrationDriver struct {
+	Tx *sql.Tx
+	Operation
+}
+
+type DriverBuilder func(tx *sql.Tx) *MigrationDriver
+

pkg/database/migrate/migrate.go

@@ -48,35 +48,12 @@ INSERT INTO migration (revision) VALUES (?)
 const deleteRevisionStmt = `
 DELETE FROM migration where revision = ?
 `
-
-// Operation interface covers basic migration operations.
-// Implementation details is specific for each database,
-// see migrate/sqlite.go for implementation reference.
-type Operation interface {
-	CreateTable(tableName string, args []string) (sql.Result, error)
-
-	RenameTable(tableName, newName string) (sql.Result, error)
-
-	DropTable(tableName string) (sql.Result, error)
-
-	AddColumn(tableName, columnSpec string) (sql.Result, error)
-
-	DropColumns(tableName string, columnsToDrop []string) (sql.Result, error)
-
-	RenameColumns(tableName string, columnChanges map[string]string) (sql.Result, error)
-}
-
 type Revision interface {
 	Up(mg *MigrationDriver) error
 	Down(mg *MigrationDriver) error
 	Revision() int64
 }
 
-type MigrationDriver struct {
-	Tx *sql.Tx
-	Operation
-}
-
 type Migration struct {
 	db   *sql.DB
 	revs []Revision
@@ -84,7 +61,7 @@ type Migration struct {
 
 type DriverFunction func(tx *sql.Tx) *MigrationDriver
 
-var Driver DriverFunction
+var Driver DriverBuilder
 
 func New(db *sql.DB) *Migration {
 	return &Migration{db: db}