Get data from a volatile layer

You can only get the latest published data from a volatile layer.

To get data from the volatile layer:

1. Create the OlpClientSettings object.

   For instructions, see Create platform client settings.

2. Create the VolatileLayerClient object with the HERE Resource Name (HRN) of the catalog that contains the layer, the layer ID, and the platform client settings from step 1.

   olp::dataservice::read::VolatileLayerClient layer_client(
   olp::client::HRN(kCatalogHRN), layer_id, client_settings);
   

3. Create the DataRequest object with the partition ID and one of the following fetch options:

   • (Default) To query network if the requested resource is not found in the cache, use OnlineIfNotFound.
   • To skip cache lookups and query the network right away, use OnlineOnly.
   • To return immediately if a cache lookup fails, use CacheOnly.
   • To return the requested cached resource if it is found and update the cache in the background, use CacheWithUpdate.

   auto request = olp::dataservice::read::DataRequest()
                      .WithPartitionId(partition_id)
                      .WithBillingTag("MyBillingTag")
                      .WithFetchOption(FetchOptions::OnlineIfNotFound);
   

4. Call the GetRequest method with the DataRequest parameter.

   auto future = layer_client.GetData(request);
   

5. Wait for the DataResponse future.

   olp::dataservice::read::DataResponse data_response =
   future.GetFuture().get();
   

The DataResponse object holds details of the completed operation and is used to determine operation success and access resultant data:

• IsSuccessful() – if the operation is successful, returns true. Otherwise, returns false.
• GetResult()– if the operation is successful, returns the following resultant data: olp::dataservice::read::DataResult
• GetError() – contains error information as a result of an error in the olp::client::ApiError object.

if (data_response.IsSuccessful()) {
    auto response_result = data_response.GetResult();
    // Handle success
} else {
    auto api_error = data_response.GetError();
    // Handle fail
}