create_or_update_unique method for Rails

create_or_update_unique.rb

# A utility method for idempotent writes with ActiveRecord.
# Add a unique Postgres or MySQL index for the fields in `unique_attributes`.
# The method will look attempt to create a record. If it fails due to a 
# unique index validation, it will update the existing record with the same
# unique attributes.

# Inpired by `create_or_find_by` in Rails 6, but serves a different use case.
# https://bigbinary.com/blog/rails-6-adds-create_or_find_by

class CreateOrUpdateUnique
  def self.call(model, unique_attributes, non_unique_attributes, &block)
    new_record = model.create!(
      unique_attributes.merge(non_unique_attributes),
    )

    yield(new_record) if block_given?

    new_record
  rescue ActiveRecord::RecordNotUnique
    existing_record = model.find_by!(
      unique_attributes
    )

    existing_record.update!(
      non_unique_attributes
    )

    existing_record
  end
end