code: func (c Columns) Writeable() *WriteableColumns {
  	w := &WriteableColumns{NewColumnsWithAlias(c.TableName, c.TableAlias)}
  	for _, col := range c.Cols {
  		if col.Writeable {
  			w.Cols[col.Name] = col
  		}
  	}
  	return w
  }
docs: // Writeable gets a list of the writeable columns from the column list.