Exporting Data as CSV

Define a Class method

For example, if you wanted to export Photos records from Photogram.

In the photo.rb model, define a class method called to_csv.

class Photo < ApplicationRecord

  # ...
  def self.to_csv
    # ...
  end
end

Choose the headers

You need to choose what headers you want to appear in the generated CSV. Create a variable called headers that contains an Array with each of the headers that you want to appear in the generated CSV.

class Photo < ApplicationRecord

  # ...
  def self.to_csv
    photos = self.all 
    headers = ["id", "caption", "image", "owner_id"]
    csv = CSV.generate(headers: true) do |csv|
      csv << headers
      # ...
    end
    return csv
  end
end

self.all is similar to Photo.all. photos determines which Photo records will enter the exported CSV.

Choose the value for each row in the CSV

For the other rows besides the header, add a loop over your list of records (photos, in this case).

Inside the loop, create an Array that represents all the data that will appear in each row. The value and order of the elements in this row Array should match the order of values in the headers.

class Photo < ApplicationRecord

  # ...
  def self.to_csv
    photos = self.all
    headers = ["id", "caption", "image", "owner_id"]
    csv = CSV.generate(headers: true) do |csv|
      csv << headers
      photos.each do |photo|
        row = []
        row.push(photo.id)
        row.push(photo.caption)
        row.push(photo.image)
        row.push(photo.owner_id)
        csv << row
      end
    end
    return csv
  end
end

Create a route to download the file

# config/routes.rb
get("/export_photos", { :controller => "photos", :action => "export" })

# app/controllers/photos_controller.rb
class PhotosController < ApplicationController
  # ...
  def export
    photos = Photo.all
    respond_to do |format|
      format.csv do 
        send_data(photos.to_csv, { :filename => "my_photos.csv"})
      end
    end
  end
  # ...
end

<a href="/export_photos.csv">Export as CSV</a>

Now clicking on “Export as CSV should open the download file dialog with the generated CSV.