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fix(driver-historian-wonderware): resolve Medium code-review finding (Driver.Historian.Wonderware-003)

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Extract the string-vs-numeric value selection from raw and at-time read
loops into a SelectValue helper method. aahClientManaged's HistoryQueryResult
has no data-type field in the bound SDK version, so the heuristic (prefer
StringValue when non-empty and Value==0) is unavoidable; the helper now
documents the limitation explicitly in its XML doc so the known edge case
(numeric tag at exactly zero with a formatted StringValue) is self-evident.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
2026-05-22 09:23:00 -04:00
parent 205b07f6aa
commit 02daacbfd0
2 changed files with 27 additions and 16 deletions
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39
src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/HistorianDataSource.cs
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@@ -316,15 +316,9 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
var result = query.QueryResult;
var timestamp = DateTime.SpecifyKind(result.StartDateTime, DateTimeKind.Utc);
object? value;
if (!string.IsNullOrEmpty(result.StringValue) && result.Value == 0)
value = result.StringValue;
else
value = result.Value;
results.Add(new HistorianSample
{
Value = value,
Value = SelectValue(result),
TimestampUtc = timestamp,
Quality = (byte)(result.OpcQuality & 0xFF),
});
@@ -453,15 +447,9 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
if (query.MoveNext(out error))
{
var result = query.QueryResult;
object? value;
if (!string.IsNullOrEmpty(result.StringValue) && result.Value == 0)
value = result.StringValue;
else
value = result.Value;
results.Add(new HistorianSample
{
Value = value,
Value = SelectValue(result),
TimestampUtc = DateTime.SpecifyKind(timestamp, DateTimeKind.Utc),
Quality = (byte)(result.OpcQuality & 0xFF),
});
@@ -574,6 +562,29 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
#pragma warning restore CS0618
}
/// <summary>
/// Selects the typed value from a <see cref="HistoryQueryResult"/> row.
/// <para>
/// <b>SDK limitation:</b> <c>HistoryQueryResult</c> exposes only <c>Value</c>
/// (double) and <c>StringValue</c> (string) — there is no tag data-type field on
/// the result. The correct approach would be to branch on the tag's declared
/// data type, but the bound version of <c>aahClientManaged</c> does not surface
/// it per query result. The heuristic below is the best available: prefer
/// <c>StringValue</c> only when it is non-empty AND <c>Value</c> is zero,
/// because string tags in the Historian SDK always project to <c>Value=0</c>
/// while numeric tags may legitimately sample to zero (in which case the SDK
/// does not populate <c>StringValue</c>). A numeric tag at exactly zero with a
/// non-empty formatted <c>StringValue</c> (e.g. "0.00") would be mis-reported
/// as a string; this is a known edge case of the SDK binding.
/// </para>
/// </summary>
private static object? SelectValue(HistoryQueryResult result)
{
if (!string.IsNullOrEmpty(result.StringValue) && result.Value == 0)
return result.StringValue;
return result.Value;
}
internal static double? ExtractAggregateValue(AnalogSummaryQueryResult result, string column)
{
switch (column)