How to format whole column for an excel using axlsx (ruby)

I am pretty new to ruby and trying to format all columns generated to text for the excel file. I have got a function as below

def writeXlsx(columnNames, templateName)
        @xlsx = Axlsx::Package.new              # create xlsx doc
        @xlsx.use_autowidth = true
        @xlsxSheet = @xlsx.workbook.add_worksheet(:name => templateName)
        @unlocked = @xlsx.workbook.styles.add_style(:locked => false)       
        @xlsxSheet.col_style(0,@unlocked)
        @xlsxSheet.add_row columnNames, :types => string


        @xlsx.serialize(File.join(@outputFolder, "#{templateName}.xlsx"))

    end

this errors out saying col_style undefined method. Can you please tell me what I am doing wrong? -ela

Copyright Notice：Content Author:「ela」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/30769487/how-to-format-whole-column-for-an-excel-using-axlsx-ruby