Delta responses is a feature on top of OData 2.0 for requesting changes. The feature is defined in OData 4.0 and this is a preliminary and lightweight implementation close to the OData 4.0 specification (see here).
How delta responses can be produced by an OData service is documented here: server side delta responses.
A client reads a feed and later wants to get only the update of changed and deleted entries.
A client has to read a complete (paged) feed. With the last feed page the service has to provide a delta link instead of a next link. A delta link us usually the same feed url containing a delta token as proprietary query parameter. With the delta link the client can query the service again and gets back a delta feed containing entries which were changed or deleted since the complete feed was received.
Example for a delta link:
Depends on the general client sample here
// retrieve a feed ODataFeed feed = client.readFeed("Container1", "Rooms", contentType); String deltaLink = feed.getFeedMetadata().getDeltaLink(); // store feed data List<ODataEntry> entries = feed.getEntries(); // get delta link from feed String deltaLink = feed.getFeedMetadata().getDeltaLink(); // query delta feed using delta link ODataDeltaFeed deltaFeed = client.readDeltaFeed("Container1", "Rooms", contentType, deltaLink); List<ODataEntry> changedEntries = deltaFeed.getEntries(); List<DeletedEntryMetada) deletedEntries = deltaFeed.getDeletedEntries(); // proceed with data handling of entries, changedEntries and deletedEntries
Precondition: Query the delta link using any HTTP client.
InputStream content = ...; // retrieve content EdmEntityContainer entityContainer = edm.getEntityContainer("Container1"); ODataFeed deltaFeed = EntityProvider.readDeltaFeed(contentType, entityContainer.getEntitySet("Rooms"), content, EntityProviderReadProperties.init().build());
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