BarbelHisto as Helper Class

The easiest way to use BarbelHisto is to integrate it as helper class for managing your persistent bi-temporal data. This alterantive is described in the Spring Boot Application helper example.

The idea is that yuo use the return value of the save() operation, which is an instance of BitemporalUpdate. This instance contains all updates happended by the save operation. It is these updates that you need to store to your database.

Here is the service implementation that uses BarbelHisto as helper class for bi-temporal data.

@Component
public class CustomerService {

    @Autowired
    private CustomerRepository customerRepository;

    public void saveCustomer(Customer customer, LocalDate from, LocalDate until) {

        // (1) create BarbelHisto helper instance
        BarbelHisto<Customer> bitemporalHelper = BarbelHistoBuilder.barbel().withMode(BarbelMode.BITEMPORAL).build();

        // (2) load active records of the current Customer journal
        bitemporalHelper.load(customerRepository.findByClientIdAndBitemporalStampRecordTimeState(customer.getClientId(),
                BitemporalObjectState.ACTIVE));

        // (3) make a bitemporal update
        BitemporalUpdate<Customer> update = bitemporalHelper.save(customer, from, until);

        // (4) replace inactivated versions
        update.getInactivations().stream().forEach(i -> customerRepository.save(i));

        // (5) prepare inserts: clear IDs of new version records
        update.getInserts().stream().forEach(d -> d.setId(null));

        // (5) perform inserts of new version data
        customerRepository.insert(update.getInserts());

    }

}

This is the minimal setup when you'd use BarbelHisto. In the example the service uses the BitemporalUpdatereturn value of the save-Operation to perform the updates to an underlying MongoCollection. There are two kinds of records returned in a BitemporalUpdateinstance. 'Inactivations' are existing records that were inactivated by the considered update to BarbelHisto. 'Inserts' are new(!) active versions. Lets go through this step-by-step:

1. The service creates an instance of BarbelHisto in BarbelMode.BITEMPORAL
2. It loads the current active(!) records of the Customer journal to BarbelHisto (here journal with the clientId "1234").
3. Then the service performs the update against BarbelHisto helper instance.

Notice, that step 3 causes some active records to be inactivated and new active records are created for the new effective periods. We need to forward those changes to the backend MongoCollection now. Currently, only the BarbelHisto helper knows about the changes. We can propagate the changes using the BitemporalUpdatereturn value of the save-operation.

4. First save inactivated records. The state of these existing(!) records changed. By performing a save operation the corresponding backend records are updated, i.e. inactivated.
5. As a last step, insert the new active records created by the bi-temporal update. An insert needs to be prepared. The new active records were copied from existing ones, therefore they carry a wrong ID in the Customer.id field. Before we insert these records into the MongoCollection, we need to clear the IDs. Afterwards records can be inserted as new records.

This is what you need to do in your service when you use BarbelHisto as helper in your backend services.