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Using Rails Console To Turn Data Into a CSV

Ian Jones

September 10, 2017


Say you have data in a Rails [4.2.8] postgres [9.6] database that you need to turn into a CSV. Rails makes it super easy to extract data through rails console.

First we want to start the console up.

rails c

Next we want to get all of the objects that we want to operate on. Say that we have a Lesson object that has these attributes:

Lesson(id: integer, title: string, youtube_id: string, summary: text, duration: integer, gist_url: text)

Say we want to get all of the lessons where the gist_url is not nil? or empty?.

With rails model helpers, thats super simple:

lessons = Lesson.where.not('gist_url' => nil, 'gist_url' => '')

Now that we have all the lessons we want to extract data from, lets extract some data.

require 'csv'
# I used the rails public folder for convinience.
file = "#{Rails.root}/public/data.csv"
lessons = Lesson.where.not('gist_url' => nil, 'gist_url' => '')
CSV.open( file, 'w' ) do |writer|
lessons.each do |l|
writer << [l.id, l.title, l.gist_url]
end
end

Now you'll have a CSV file in your /public folder named data.csv.

Lets say you already have a CSV file that you want to access from the Rails console.

Heres how you load the CSV into memory:

require 'csv' # not required if you already did this
csv_text = File.read("#{Rails.root}/public/data.csv")
csv = CSV.parse(csv_text, :headers => true)
csv.each do |row|
# do some work
end

Row will be an array of the values that are in that row. You're CSV had [id, title, gist_url] you could access id with row[0], title with row[1] and gist_url with row[2] ect.

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