fix import cycle

db/column/column.go

@@ -63,6 +63,7 @@ func NewColumn(option config.ColumnOptions) (Column, error) {
 		option.DbMemoryOptions.ColumnName = "default"
 	}
 
+	// set wal, the wal is a global wal of all column family
 	option.DbMemoryOptions.Wal = w
 
 	// create a new db
@@ -93,6 +94,7 @@ func (c *column) CreateColumnFamily(name string) error {
 	if _, ok := c.columnFamily[name]; ok {
 		return errors.New("column family already exists")
 	}
+	c.option.DbMemoryOptions.ColumnName = name
 	db, err := memory.NewDB(c.option.DbMemoryOptions)
 	if err != nil {
 		return err
@@ -107,6 +109,10 @@ func (c *column) DropColumnFamily(name string) error {
 	if _, ok := c.columnFamily[name]; !ok {
 		return errors.New("column family not exists")
 	}
+	err := os.RemoveAll(c.option.DbMemoryOptions.Option.DirPath + "/" + name)
+	if err != nil {
+		return err
+	}
 	delete(c.columnFamily, name)
 	return nil
 }

db/memory/db.go

@@ -20,14 +20,19 @@ type Db struct {
 	errMsgCh    chan []byte
 }
 
+// NewDB create a new db of wal and memTable
 func NewDB(option config.DbMemoryOptions) (*Db, error) {
+	// create a new memTable
 	mem := NewMemTable()
+	// dir path has been changed to dir path + column name
 	option.Option.DirPath = option.Option.DirPath + "/" + option.ColumnName
 	db, err := engine.NewDB(option.Option)
 	if err != nil {
 		return nil, err
 	}
 	w := option.Wal
+	// if wal is nil, create a new wal
+	// if wal is not nil, the wal was created by column family
 	if option.Wal == nil {
 		walOptions := wal.Options{
 			DirPath:  option.Option.DirPath,