genmai.go
func (db *DB) columnFromTag(field reflect.StructField) string {
	col := field.Tag.Get(dbColumnTag)
	if col == "" {
		return stringutil.ToSnakeCase(field.Name)
	}
	return col
}
func (db *DB) columnFromTag(field reflect.StructField) string {
	col := field.Tag.Get(dbColumnTag)
	if col == "" {
		return stringutil.ToSnakeCase(field.Name)
	}
	return col
}
// columnFromTag returns the column name.
// If "column" tag specified to struct field, returns it.
// Otherwise, it returns snake-cased field name as column name.