2 Using the StreamOperation Class

A streams application works by implementing Subscribers. Subscribers receive a stream of events that consist of write operations to a table of interest.

For more information, see Implementing Subscribers.

Every event your application receives in the subscription stream is represented as an oracle.kv.pubsub.StreamOperation. Each of these events represents either a put or delete operation on the table that your application subscribes to.

For more information, see oracle.kv.pubsub.StreamOperation class summary in the — Java Direct Driver API Reference

The StreamOperation interface provides the following methods:

• StreamOperation.getType()

  Returns a StreamOperation.Type object. This is an enum constant that is either delete or put. For example:

  // so is a StreamOperation object. It is obtained using
  // NoSQLSubscriber.onNext().
  switch (so.getType()) {
      case PUT:
          {
              // Process the put operation here.
          }
          break;
      case DELETE:
          {
              // Process the delete operation here.
          }
          break;
      default:
          // Received an unknown and therefore illegal operation type.
          throw new IllegalStateException("... exception message ...");
  } 

• StreamOperation.asDelete()

  Returns the operation as a StreamOperation.DeleteEvent object. The object contains only the Primary Key associated with the delete operation:

  // so is a StreamOperation object. It is obtained using
  // NoSQLSubscriber.onNext().
  StreamOperation.DeleteEvent de = so.asDelete();
  PrimaryKey pk = de.getPrimaryKey();

• StreamOperation.asPut()

  Returns the operation as a StreamOperation.PutEvent object. This object allows you to obtain the row that was changed by the put operation. Be aware that the row returned here represents the state of the row after the put operation has been performed:

  // so is a StreamOperation object. It is obtained using
  // NoSQLSubscriber.onNext().
  StreamOperation.PutEvent pe = so.asPut();
  Row row = pe.getRow();

• StreamOperation.getRepGroupId()

  Returns the Shard ID (as an int) where this write operation was performed.

• StreamOperation.getSequenceId()

  Returns the unique sequence ID associated with this operation. This ID uniquely identifies a stream operation associated with a given Publisher.

  These IDs can be used to sequence operations seen for a given key. The Subscription API guarantees that the order of events for a particular key is the same as the order in which these operations were applied in Oracle NoSQL Database. The subscription API provides no guarantees about the order of operations beyond the single key.