How to convert array of ActiveRecord models to CSV?

Question

I got an array of ActiveRecord models that I wish to convert to a CSV. I tried researching gems like FasterCSV, but they just seem to work with strings and arrays, not ActiveRecord models.

In short, I want to convert:

user1 = User.first
user2 = User.last
a = [user1, user2]

TO:

   id,username,bio,email
    1,user1,user 1 bio,user1 email
    1,user2,user 2 bio,user2 email

Is there an easy Rails way to do this?

Solution 1

The following will write the attributes of all users to a file:

CSV.open("path/to/file.csv", "wb") do |csv|
  csv << User.attribute_names
  User.find_each do |user|
    csv << user.attributes.values
  end
end

Similarly you could create a CSV string:

csv_string = CSV.generate do |csv|
  csv << User.attribute_names
  User.find_each do |user|
    csv << user.attributes.values
  end
end

Solution 2

@rudolph9's answer is really awesome. I just want to leave a note for people who need to do this task periodically: making it as a rake task would be a good idea!

lib/tasks/users_to_csv.rake

# usage:
# rake csv:users:all => export all users to ./user.csv
# rake csv:users:range start=1757 offset=1957 => export users whose id are between 1757 and 1957
# rake csv:users:last number=3   => export last 3 users
require 'csv' # according to your settings, you may or may not need this line

namespace :csv do
  namespace :users do
    desc "export all users to a csv file"
    task :all => :environment do
      export_to_csv User.all
    end

    desc "export users whose id are within a range to a csv file"
    task :range => :environment do |task, args|
      export_to_csv User.where("id >= ? and id < ?", ENV['start'], ENV['offset'])
    end

    desc "export last #number users to a csv file"
    task :last => :environment do |task, arg|
      export_to_csv User.last(ENV['number'].to_i)
    end

    def export_to_csv(users)
      CSV.open("./user.csv", "wb") do |csv|
        csv << User.attribute_names
        users.each do |user|
          csv << user.attributes.values
        end
      end
    end
  end
end

Solution 3

This might be off the original question but solve the problem. If you plan to make all or some of your Active Record models be able to convert to csv, you can use ActiveRecord concern. An example is shown below

module Csvable
  extend ActiveSupport::Concern 

  class_methods do
    def to_csv(*attributes)
      CSV.generate(headers: true) do |csv| 
        csv << attributes 

        all.each do |record| 
          csv << attributes.map { |attr| record.send(attr) }
        end 
      end
    end
  end
end

The attribute provided will be used as the header for the CSV and it is expected that this attribute corresponds to methods name in the included class. Then you can include it in any ActiveRecord class of your choice, in this case, the User class

class User 
  include Csvable 

end

Usage

User.where(id: [1, 2, 4]).to_csv(:id, :name, :age)

Note: This only works for ActiveRecord relation and not for arrays

Solution 4

If you need something quick and dirty, not so much for production as just grabbing some data for a non-technical user, you could paste this in console:

require 'csv'
class ActiveRecord::Relation
  def to_csv
    ::CSV.generate do |csv|
      csv << self.model.attribute_names
      self.each do |record|
        csv << record.attributes.values
      end
    end
  end
end

Then do: User.select(:id,:name).all.to_csv

If you were going to production, I'd probably turn this into a decorator around ActiveRecord::Relation and more precisely ensuring that the order of your fields/attributes.

Solution 5

with julia_builder you can configure a csv export pretty easily.

class UserCsv < Julia::Builder
  # specify column's header and value
  column 'Birthday', :dob
  # header equals 'Birthday' and the value will be on `user.dbo`

  # when header and value are the same, no need to duplicate it.
  column :name
  # header equals 'name', value will be `user.name`

  # when you need to do some extra work on the value you can pass a proc.
  column 'Full name', -> { "#{ name.capitalize } #{ last_name.capitalize }" }

  # or you can pass a block
  column 'Type' do |user|
    user.class.name
  end
end

and then

users = User.all
UserCsv.build(users)

View more solutions

Comments

[Stefan]

You can just use csv << user.attributes.values

[Henley]

How can I render this CSV string in my controller? In other words I want the page to return a CSV to the user.

[rudolph9]

@HenleyChiu Checkout comma, it enables you to render CSV data the "rails-way" respond_to { |format| format.csv { render :csv => User.limited(50) }}

[Mike Glenn]

This fails with a "NoMethodError: undefined method 'model' for ActiveRecord::Relation" if you use it on a named scope instead of .all. Anyone have a suggested fix?

[Mario Olivio Flores]

Hum... In what context are you calling this? Perhaps you're loading this before AR had actually loaded somehow? Since model is an attribute on AR::R, maybe it is not set when the results are empty. Are you sure there are records in your returned result? You could also try calling all on your named scope, but I'd be surprised if they helped.

[Mike Glenn]

Its the same context that the .all.to_csv works in, I just change .all to a named scope I have defined in the model. it has something to do with the scope creating a proxy object, but I was unable to get much further in digging into the issue. Its not a show stopper for me but it would be nice to figure out a way to make it work, since it is a generic and very elegant solution.

[davkutalek]

This is the best answer: find_each batches your sql queries so that you don't use massive amounts of memory

[davkutalek]

This will load all your users into memory. If you have a ton of records @YukiInoue has the better answer

[rudolph9]

@davkutalek good point. I just updated may answer to make use of #find_each like @Yukilnoue . Thank you for pointing that out apidock.com/rails/ActiveRecord/Batches/find_each