CSV files are comma separated values file that stores the data values in tabular format, where each column values are separated by commas. They are the lightest way of storing data in tabular format that is why most of the bulk data are exported and imported in this format. Rails also provides support for importing the data and exporting the data in csv format.

All the csv operations in rails are performed by requiring the "csv" in the application. So you need to require it somewhere in application.rb or anyother place wherever you need to use it.

require 'csv'

Exporting Data in CSV format:

For exporting data in csv format, here we are taking example of a product table that contains id, name and description. Suppose you want to export these 3 details of products in csv format. Then first we will create a class method in our model like this:

class Product < ActiveRecord::Base
  def self.to_csv
      # Select the attributes that are needed in csv
      attribs = %w{id name description}

    # iterate over all the passed products and one by one create row of the csv
    CSV.generate(headers: true) do |csv|
      csv << attribs
      all.each do |product|
        csv << attribs.map{ |attr| product.send(attr) }
      end
    end
  end
end

Now you need to call the method in a controller or wherever you want to give the output in a csv file like this:

class ProductsController < ApplicationController
  def index
    @products = Product.all
    respond_to do |format|
      format.html
      format.csv { send_data @products.to_csv, filename: "products.csv" }
    end
  end
end

Now whenever a request comes with type csv a products.csv file will get downloaded containing all the id,name,description of the products
 

Importing Data from CSV:

As exporting the csv fetches each row and writes each row in the csv format, similarly in case importing we need to read each line of the csv and create corresponding record. So there will 3 steps for this:

a) Read the csv file
b) Parse the file and create an array of records
c) Iterate over the array and store the records into the table

Thus in our case we can do this like:

# Read the file
file_content = File.read('file_path')

# Parse the content, set headers true if csv contains headers
csv = CSV.parse(file_content, :headers => true)

# Iterate over csv and create records
csv.each do |row|
  Product.create!(row.to_hash)
end

Thus we can import and export data in csv format.

Hope you liked reading this.