What Is the Changes API

The changes subscription is accessible by a document store through its IDatabaseChanges interface.

IDatabaseChanges changes();

IDatabaseChanges changes(String database);

IDatabaseChanges inherits from IConnectableChanges<TChanges> interface that represent the connection.

public interface IConnectableChanges<TChanges extends IDatabaseChanges> extends CleanCloseable {

    boolean isConnected();

    void ensureConnectedNow();

    void addConnectionStatusChanged(EventHandler<VoidArgs> handler);

    void removeConnectionStatusChanged(EventHandler<VoidArgs> handler);

    void addOnError(Consumer<Exception> handler);

    void removeOnError(Consumer<Exception> handler);
}

To receive notifications regarding server-side events, subscribe using one of the following methods.

• forAllDocuments
• forAllIndexes
• forAllOperations
• forDocument
• forDocumentsInCollection
• forDocumentsStartingWith
• forIndex
• forOperationId

To end a subscription (stop listening for particular notifications) you must close the subscription.

IDatabaseChanges subscription = store.changes();

subscription.ensureConnectedNow();

subscription.forAllDocuments().subscribe(Observers.create(change -> {
    System.out.println(change.getType() + " on document " + change.getId());
}));

try {
    // application code here
} finally {
    if (subscription != null) {
        subscription.close();
    }
}

Changes API and Data Subscription are services that a RavenDB Server provides subscribing clients.
Both services respond to events that take place on the server, by sending updates to their subscribers.

• Changes API is a Push Notifications Service.

  • Changes API subscribers receive notifications regarding events that took place on the server, without receiving the actual data entities affected by these events.
    For the modification of a document, for example, the client will receive a DocumentChange object with details like the document's ID and collection name.

  • The server does not keep track of sent notifications or checks clients' usage of them. It is a client's responsibility to manage its reactions to such notifications.

• Data Subscription is a Data Consumption Service.

  • A Data Subscription task keeps track of document modifications in the database and delivers the documents in an orderly fashion when subscribers indicate they are ready to receive them.
  • The process is fully managed by the server, leaving very little for the subscribers to do besides consuming the delivered documents.