/// <summary>
/// Creates a new <see cref="RedisTagDefinition"/> object.
/// </summary>
/// <param name="historian">The owning historian.</param>
/// <param name="id">The tag ID.</param>
/// <param name="settings">The tag settings.</param>
/// <param name="metadata">The metadata for the tag.</param>
/// <param name="initialTagValues">The initial tag values, used to prime the exception and compression filters for the tag.</param>
/// <param name="changeHistory">The change history for the tag.</param>
private RedisTagDefinition(RedisHistorian historian, string id, TagSettings settings, TagMetadata metadata, InitialTagValues initialTagValues, IEnumerable <TagChangeHistoryEntry> changeHistory) : base(historian, id, settings, metadata, CreateTagSecurity(), initialTagValues, changeHistory)
{
_historian = historian ?? throw new ArgumentNullException(nameof(historian));
_tagDefinitionKey = _historian.GetKeyForTagDefinition(Id);
_snapshotKey = _historian.GetKeyForSnapshotData(Id);
_archiveKey = _historian.GetKeyForRawData(Id);
_archiveCandidateKey = _historian.GetKeyForArchiveCandidateData(Id);
_archiveCandidateValue = new ArchiveCandidateValue(initialTagValues?.LastExceptionValue, initialTagValues?.CompressionAngleMinimum ?? Double.NaN, initialTagValues?.CompressionAngleMaximum ?? Double.NaN);
Updated += TagUpdated;
}
/// <summary>
/// Loads the last-archived value for the specified tag.
/// </summary>
/// <param name="historian">The historian.</param>
/// <param name="tagId">The tag ID.</param>
/// <param name="cancellationToken">The cancellation token for the request.</param>
/// <returns>
/// A task that will return the last-archived value for the tag.
/// </returns>
private static async Task <TagValue> LoadLastArchivedValue(RedisHistorian historian, string tagId, CancellationToken cancellationToken)
{
var key = historian.GetKeyForRawData(tagId);
var lastArchivedValueTask = historian.Connection.GetDatabase().SortedSetRangeByScoreAsync(key, Double.NegativeInfinity, Double.PositiveInfinity, Exclude.None, Order.Descending, 0, 1, CommandFlags.None);
await Task.WhenAny(lastArchivedValueTask, Task.Delay(-1, cancellationToken)).ConfigureAwait(false);
cancellationToken.ThrowIfCancellationRequested();
var value = lastArchivedValueTask.Result.FirstOrDefault();
return(value == RedisValue.Null
? null
: JsonConvert.DeserializeObject <RedisTagValue>(value)?.ToTagValue());
}
