Loading CSV Data in Rails: Then vs Now

Note (2025): This post was originally written in the Rails 2.3.8 era. While the overall idea of loading CSV data into Rails models remains relevant, the code shown is outdated. FasterCSV has been merged into Ruby’s built-in CSV class, and Rails now provides bulk insert methods (insert_all, upsert_all) that make the process far more efficient. What follows is both the legacy approach and the modern Rails way.

The Legacy Approach (Rails 2.x)

Back in the Rails 2.3.8 days, when we needed to load data from multiple files into our models. Each file represented a dataset, and every row needed to be mapped to attributes in the model.

Example workflow:

1. Map file names to models.
2. Iterate over rows in each CSV.
3. Save records row by row.

files = {
  "users.csv" => User,
  "products.csv" => Product
}

files.each do |file, model|
  FasterCSV.foreach(file, :headers => true) do |row|
    model.create!(row.to_hash)
  end
end

This worked, but it was:

• Dependent on FasterCSV (now obsolete).
• Saving records one by one (slow for large datasets).
• Using custom helpers that are unnecessary today.

The Modern Rails Way (Rails 7/8)

In modern Rails (7+), you can rely on built-in CSV and bulk insert methods:

require "csv"

files = {
  "users.csv" => User,
  "products.csv" => Product
}

files.each do |file, model|
  rows = CSV.read(file, headers: true).map(&:to_h)
  model.insert_all(rows)
end

Why this is better:

• No extra gems needed — CSV is part of Ruby stdlib.
• Use row.to_h directly (no need for custom array-to-hash helpers).
• Efficient bulk inserts with insert_all (or upsert_all if handling duplicates).
• Cleaner and more performant.

Quick Comparison

Takeaway

• If you’re on a legacy Rails app, the old approach might look familiar.
• On modern Rails, always use CSV + bulk inserts.
• Even better, for very large datasets, consider background jobs (Sidekiq/Resque) to process imports asynchronously.

You might also like

• Connecting to Multiple Databases in a Rails App
• Working with Files in Ruby