Bulk Upsert in Ruby/Rails

The upsert gem is great for individual upserts, but for performant bulk upserts, use the activerecord-import gem.

Add a unique index on the columns to upsert on (if it’s not your primary key)

class AddUpsertIndexOnForecasts < ActiveRecord::Migration[5.2]
  def change
    add_index :forecasts, [:date], unique: true
  end
end

Prep your records

records = [
  {date: "2018-01-01", value: 10},
  {date: "2018-02-01", value: 15},
  {date: "2018-03-01", value: 23}
]

For PostgreSQL 9.5+ and SQLite 3.24+, do:

Forecast.import(records,
  validate: false,
  on_duplicate_key_update: {
    conflict_target: [:date],
    columns: [:value]
  }
)

For MySQL, do:

Forecast.import(records,
  validate: false,
  on_duplicate_key_update: [:value]
)

Official docs