Export Records to CSV Files with Rails

Learn how to export records into CSV files using Ruby on Rails. Here are the steps.

Steps:

1. Add a controller and make sure you handle the csv request.
2. Add a route to point to your controller
3. Add a model with the class method to_csv

---

Lets code it!

Controller

# users_controller.rb

class UsersController < ApplicationController
  def index
    @users = User.all

    respond_to do |format|
      format.html
      format.csv { send_data @users.to_csv, filename: "users-#{Date.today}.csv" }
    end
  end

Routes

# routes.rb

...

resources :users, only: :index

...

Model

# user.rb

class User < ActiveRecord::Base
  def self.to_csv
    attributes = %w{id email name}

    CSV.generate(headers: true) do |csv|
      csv << attributes

      all.find_each do |user|
        csv << attributes.map{ |attr| user.send(attr) }
      end
    end
  end

  def name
    "#{first_name} #{last_name}"
  end
end

Core custom methods:

to_csv will map out the "id, email, name" values of your model collection and then generate a CSV string.

---

Rails core methods for this feature:

#send_data Sends the given binary data to the browser. This method is similar to render :text => data, but also allows you to specify whether the browser should display the response as a file attachment (i.e. in a download dialog) or as inline data. You may also set the content type, the apparent file name, and other things. Source

Comments

[haroldus-]

How about doing this as a concern instead?

# models/concerns/generate_csv.rb
module GenerateCSV
  extend ActiveSupport::Concern

  class_methods do
    def generate_csv
      CSV.generate(headers: true) do |csv|
        csv << self.attribute_names

        all.each do |record|
          csv << record.attributes.values
        end
      end
    end
  end
end

Then

# models/user.rb
class User
  include GenerateCSV
end

or

# models/whatever.rb
class Whatever
 include GenerateCSV
end

[countalucard2022]

Great for DRY approach, thanks for this :)

[Thomas R. Koll]

Nitpicking if I may, a missing last or first name won't be noticed in HTML but it will be noticed in CSV when a human reads it directly or imported in Excel/LibreCalc.

def name
  [first_name, last_name].compact.join(' ')
end

[Nuno]

Nice, but there's a mistake in the controller/ model. The code appears to work because @users=User.all which matches the set of users computed within the model class

The correct call would be User.to_csv(@users). The User model function has to be modified to take the new parameter into account.

[Victor Hazbun]

nope, it's right the way it is. Since @users is an ActiveRecord::Relation so you can say @users.to_csv

[Von Christian]

How to run it in background job(Sidekiq) ?

[Victor Hazbun]

It depends, are you going to send an email on a background job? or are you going to upload the file on S3? please give some context.

[Von Christian]

from my experience, when large amounts of data is involved, the server times out. Im thinking if it is possible to move the CSV export and show a download link to the user?

[Victor Hazbun]

Ok, then you will need to do the following:

1. On a BG job generate the CSV file
2. Upload the file to AWS S3
3. Save the URL in the DB
4. Expose the URL in the front-end

[Victor Hazbun]

UPDATE: I was using #each, I changed it to#find_each which saves memory. See api.rubyonrails.org/classes/Active...

[countalucard2022]

But this will not be a report friendly, find_each forces the sequence to be order by id desc :( thanks to the postoverall!