script.rb

@client.query_in_batches("SELECT * FROM Invoice", per_page: 1000) do |records|
  records.entries.each do |record|
    # Record has an active class
    if record.class_ref.present? && !record.class_ref.name.match(/supprimé/)
      reference = record.class_ref

      # Find project & organisation
      project = Project.find_by!(quickbooks_class_id: reference.value)
      organisation = project.organisation

      # Update record line
      record.customer_ref = Quickbooks::Model::BaseReference.new(project.quickbooks_id)
      record.class_ref = nil

      # Partially update record
      @client.update(record, sparse: true)
    end
  end
end

Using this API client: https://github.com/ruckus/quickbooks-ruby