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CSV Import for humans on Ruby / Ruby on Rails

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Importing a CSV file is easy to code until real users attempt to import real data.

CSVImporter aims to handle validations, column mapping, import and reporting.

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Importing CSV files seems easy until you deal with real users uploading their real CSV file. You then have to deal with ASCII-8BIT formats, missing columns, empty rows, malformed headers, wild separators, etc. Reporting progress and errors to the end-user is also key for a good experience.

I went through this many times so I decided to build CSV Importer to save us the trouble.

CSV Importer provides:

  • a DSL to define the mapping between CSV columns and your model
  • good reporting to the end user
  • support for wild encodings and CSV formats.

It is compatible with ActiveRecord 4+ and any ORM that implements the class methods

and the instance method

Usage tldr;

Define your CSVImporter:

class ImportUserCSV
  include CSVImporter

model User # an active record like model

column :email, to: ->(email) { email.downcase }, required: true column :first_name, as: [ /first.?name/i, /pr(é|e)nom/i ] column :last_name, as: [ /last.?name/i, "nom" ] column :published, to: ->(published, user) { user.published_at = published ? : nil }

identifier :email # will update_or_create via :email

when_invalid :skip # or :abort end

Run the import:

import = my_file)

import.valid_header? # => false # => "The following columns are required: email"

Assuming the header was valid, let's run the import!! # => true # => "Import completed. 4 created, 2 updated, 1 failed to update"


Add this line to your application's Gemfile:

gem 'csv-importer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install csv-importer


Create an Importer

Create a class and include

class ImportUserCSV
  include CSVImporter

Associate an active record model


is likely to be an active record model.
class ImportUserCSV
  include CSVImporter

model User end

It can also be a relation which is handy to preset attributes:

class User
  scope :pending, -> { where(status: 'pending') }

class ImportUserCSV include CSVImporter

model User.pending end

You can change the configuration at runtime to scope down to associated records.

class Team
  has_many :users

team = Team.find(1) "tmp/my_file.csv") do model team.users end

Define columns and their mapping

This is where the fun begins.

class ImportUserCSV
  include CSVImporter

model User

column :email end

This will map the column named email to the email attribute. By default, we downcase and strip the columns so it will work with a column spelled " EMail ".

Now, email could also be spelled "e-mail", or "mail", or even "courriel" (oh, canada). Let's give it a couple of aliases then:

  column :email, as: [/e.?mail/i, "courriel"]

Nice, emails should be downcased though, so let's do this.

  column :email, as: [/e.?mail/i, "courriel"], to: ->(email) { email.downcase }

If you need to do more advanced stuff, you've got access to the model:

  column :email, as: [/e.?mail/i, "courriel"], to: ->(email, user) { = email.downcase; model.super_user! if email[/\z/] }

Like very advanced stuff? We grant you access to the

object itself which contains the column name – quite handy if you want to support arbitrary columns.

  column :extra, as: [/extra/], to: ->(value, user, column) do
    attribute =^extra /, '')
    user[attribute] = value

Note that

accepts anything that responds to call and take 1, 2 or 3 arguments.
class ImportUserCSV
  include CSVImporter

model User

column :birth_date, to: DateTransformer column :renewal_date, to: DateTransformer column :next_renewal_at, to: ->(value) { } end

class DateTransformer def Date.strptime(date, '%m/%d/%y') end end

Now, what if the user does not provide the email column? It's not worth running the import, we should just reject the CSV file right away. That's easy:

class ImportUserCSV
  include CSVImporter

model User

column :email, required: true end

import = "name\nbob") import.valid_header? # => false # => :invalid_header # => "The following columns are required: 'email'"

Update or Create

You often want to find-and-update-or-create when importing a CSV file. Just provide an identifier, and we'll do the hard work for you.

class ImportUserCSV
  include CSVImporter

model User

column :email, to: ->(email) { email.downcase }

identifier :email end

And yes, we'll look for an existing record using the downcased email. :)

You can also define a composite identifier:

  # Update records with matching company_id AND employee_id
  identifier :company_id, :employee_id

Or a Proc:

  # Update records with email if email is present
  # Update records matching company_id AND employee_id if email is not present
  identifier ->(user) { ? [:company_id, :employee_id] : :email }

Skip or Abort on error

By default, we skip invalid records and report errors back to the user. There are times where you want your import to be an all or nothing. The

option is here for you.
class ImportUserCSV
  include CSVImporter

model User

column :email, to: ->(email) { email.downcase }

when_invalid :abort end

import = "email\[email protected]\nINVALID_EMAIL") import.valid_header? # => true! # => false # => :aborted # => "Import aborted"

You are now done defining your importer, let's run it!

Import from a file, path or string

You can import from a file, path or just the CSV content. Please note that we currently load the entire file in memory. Feel free to contribute if you need to support CSV files with millions of lines! :)

import = my_file)
import = "tmp/new_users.csv")
import = "email,name\[email protected],bob")

Overwrite configuration at runtime

It is often needed to change the configuration at runtime, that's quite easy:

team = Team.find(1)
import = my_file) do
  model team.users


You can preset attributes (or perform any changes to the model) at configuration or runtime using

class ImportUserCSV
  model User

column :email

after_build do |user| = email.split('@').first end end

assuming current_user is available

import = my_file) do after_build do |user| user.created_by_user = current_user end end


callback is run after each call to the method
no matter it fails or succeeds. It is quite handy to keep track of progress.
progress_bar = my_file) do after_save do |user| progress_bar.increment end end

Skip import

You can skip the import of a model by calling

in an
block: csv_file) do
  # Skip existing records
  after_build do |user|
    skip! if user.persisted?

Validate the header

On a web application, as soon as a CSV file is uploaded, you can check if it has the required columns. This is handy to fail early and provide the user with a meaningful error message right away.

import = params[:csv_file])
import.valid_header? # => false # => "The following columns are required: "email""

Run the import and provide feedback to the user

import = params[:csv_file])!  # => "Import completed. 4 created, 2 updated, 1 failed to update"

You can get your hands dirty and fetch the errored rows and the associated error message: { |row| [row.line_number,, row.errors] }
  # => [ [2, "INVALID_EMAIL", { "email" => "is invalid" } ] ]

We do our best to map the errors back to the original column name. So with the following definition:

  column :email, as: /e.?mail/i

and csv:


The error returned should be:

{ "E-Mail" => "is invalid" }

Custom quote char

You can handle exotic quote chars with the

[email protected],'bob "elvis" wilson'
import = csv_content)!
  # => :invalid_csv_file
  # => CSV::MalformedCSVError: Illegal quoting in line 2.

Let's provide a valid quote char:

import = csv_content, quote_char: "'")!
  # => [ ["[email protected]", "bob \"elvis\" wilson"] ]

Custom encoding

You can handle exotic encodings with the

option. "メール,氏名".encode('SJIS'), encoding: 'SJIS:UTF-8')


After checking out the repo, run

to install dependencies. Then, run
for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run

bundle exec rake install
. To release a new version, update the version number in
, and then run
bundle exec rake release
to create a git tag for the version, push git commits and tags, and push the
file to


  1. Fork it ( )
  2. Create your feature branch (
    git checkout -b my-new-feature
  3. Commit your changes (
    git commit -am 'Add some feature'
  4. Push to the branch (
    git push origin my-new-feature
  5. Create a new Pull Request

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