require "active_record"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Migration.class_eval do
  create_table(:records) do |t|
    t.string :column
  end
end

data = 50_000.times.map { |i| Hash[column: "Column #{i}"] }

# =============================================================

class Record < ActiveRecord::Base
end

Record.create(data)

# Takes 60 seconds, because it's instantiating all the ActiveRecord::Base objects