/// <summary>
/// Query to subtract the oldest value of a OPC UA node
/// from the newest value in the search span
/// </summary>
/// <param name="searchSpan">Date and time span for the query</param>
/// <param name="appUri">The OPC UA server application Uri</param>
/// <param name="nodeId">The node id in the OPC UA server namespace</param>
/// <returns>The difference</returns>
public async Task <double> DiffQuery(DateTimeRange searchSpan, string appUri, string nodeId)
{
try
{
PredicateStringExpression expression = new PredicateStringExpression(
String.Format(OpcServerNodePredicate, appUri, nodeId));
BaseLimitClause firstMember = new TopLimitClause(1,
new[]
{
new SortClause(new BuiltInPropertyReferenceExpression(BuiltInProperty.Timestamp),
SortOrderType.Asc)
});
BaseLimitClause lastMember = new TopLimitClause(1,
new[]
{
new SortClause(new BuiltInPropertyReferenceExpression(BuiltInProperty.Timestamp),
SortOrderType.Desc)
});
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
Task <IEnumerable <IEvent> > firstTask = RDXQueryClient.GetEventsAsync(
searchSpan,
expression,
firstMember,
_cancellationToken);
Task <IEnumerable <IEvent> > lastTask = RDXQueryClient.GetEventsAsync(
searchSpan,
expression,
lastMember,
_cancellationToken);
await Task.WhenAll(new Task[] { firstTask, lastTask });
IEnumerable <IEvent> firstEvent = firstTask.Result;
IEnumerable <IEvent> lastEvent = lastTask.Result;
stopwatch.Stop();
RDXTrace.TraceInformation("DiffQuery queries took {0} ms", stopwatch.ElapsedMilliseconds);
long first = GetValueOfProperty <long>(firstEvent.First <IEvent>(), OpcMonitoredItemValue);
long last = GetValueOfProperty <long>(lastEvent.First <IEvent>(), OpcMonitoredItemValue);
return(last - first);
}
catch (Exception e)
{
RDXTrace.TraceError("DiffQuery Exception {0}", e.Message);
return(0);
}
}
/// <summary>
/// Helper to query for last event of given station and nodeid
/// </summary>
private Task <IEnumerable <IEvent> > GetLatestEvent(DateTime endTime, string appUri, string nodeId)
{
PredicateStringExpression expression = new PredicateStringExpression(
String.Format(OpcServerNodePredicate, appUri, nodeId));
DateTimeRange searchSpan = new DateTimeRange(endTime.Subtract(TimeSpan.FromDays(360)), endTime);
BaseLimitClause lastMember = new TopLimitClause(1,
new[]
{
new SortClause(new BuiltInPropertyReferenceExpression(BuiltInProperty.Timestamp),
SortOrderType.Desc)
});
return(RDXQueryClient.GetEventsAsync(
searchSpan,
expression,
lastMember,
_cancellationToken));
}