Using disk persistence

BarbelHistois based on CqEngine collections. These collections can be stored persitent on disk. They use an SQLite database to achieve this, so storing data to disk also provides transaction isolation. Refer to the CqEngine documentation to go into details about all the option.

The code snipped below shows an example how to configure disk persistence with BarbelHisto.

// define primary key in POJO class -> versionID !
SimpleAttribute<DefaultPojo, String> primaryKey = 
   new SimpleAttribute<DefaultPojo, String>("versionId") 
      {
        public String getValue(DefaultPojo object, QueryOptions queryOptions) {
            return (String) ((Bitemporal) object).getBitemporalStamp().getVersionId();
       };
// make BarbelHisto backbone persistent and register 
// Mongo update listener with asynchronous bus
BarbelHisto<DefaultPojo> histo = BarbelHistoBuilder.barbel()
        .withBackboneSupplier(() -> new ConcurrentIndexedCollection<>
            (
            DiskPersistence.onPrimaryKeyInFile(primaryKey, new File("test.dat"))
            );

First you need to define a primaryKey. The versionIdshould become the primary key. Then define a custom persistent backbone collection with BarbelHistoBuilder.withBackboneSupplier. Notice that you have to define a Supplier cause BarbelHisto decides when to construct the backbone collection. The DefaultPojo uses the @PersistenceConfig annotation on type level which is mandatory when ever you want to use DiskPersistence with BarbelHisto.

@PersistenceConfig(serializer = BarbelPojoSerializer.class, polymorphic = true)

The annotation causes BarbelHisto to register a specific serializer with CqEngine collections to make sure that all the version data is stored correctly when using BarbelMode.POJO. IN BarbelMode.BITEMPORALthis annotation will not be required.