code: public Observable<List<UsageInner>> listUsagesAsync(String resourceGroupName, String accountName, String databaseRid, String filter) {
          return listUsagesWithServiceResponseAsync(resourceGroupName, accountName, databaseRid, filter).map(new Func1<ServiceResponse<List<UsageInner>>, List<UsageInner>>() {
              @Override
              public List<UsageInner> call(ServiceResponse<List<UsageInner>> response) {
                  return response.body();
              }
          });
      }
docs: Retrieves the usages (most recent data) for the given database.
  
  @param resourceGroupName Name of an Azure resource group.
  @param accountName Cosmos DB database account name.
  @param databaseRid Cosmos DB database rid.
  @param filter An OData filter expression that describes a subset of usages to return. The supported parameter is name.value (name of the metric, can have an or of multiple names).
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the List&lt;UsageInner&gt; object