How to Efficiently Truncate Milliseconds from a .NET DateTime Object?

Handling Millisecond Discrepancies in .NET DateTime Objects

When comparing timestamps received from external requests with database values (e.g., SQL Server), precision differences can lead to comparison issues. This often stems from the database's millisecond precision, which may not be present in the incoming data. To rectify this, removing milliseconds from the .NET DateTime object is necessary.

A concise solution involves directly manipulating the Ticks property:

<code class="language-csharp">DateTime dateTime = ...; // Your DateTime object
dateTime = new DateTime(dateTime.Ticks - (dateTime.Ticks % TimeSpan.TicksPerSecond), dateTime.Kind);</code>

Alternatively, a slightly more readable version achieves the same result:

<code class="language-csharp">dateTime = dateTime.AddTicks(-(dateTime.Ticks % TimeSpan.TicksPerSecond));</code>

Both methods effectively truncate milliseconds while preserving the Kind property (Local, Utc, or Unspecified).

For enhanced reusability, consider creating an extension method:

<code class="language-csharp">public static DateTime TruncateMilliseconds(this DateTime dateTime, TimeSpan timeSpan)
{
    if (timeSpan == TimeSpan.Zero) return dateTime; // Handle zero TimeSpan

    if (dateTime == DateTime.MinValue || dateTime == DateTime.MaxValue) return dateTime; // Preserve special values

    return dateTime.AddTicks(-(dateTime.Ticks % timeSpan.Ticks));
}</code>

This extension method allows for flexible truncation:

<code class="language-csharp">dateTime = dateTime.TruncateMilliseconds(TimeSpan.FromMilliseconds(1)); // Truncate to whole milliseconds
dateTime = dateTime.TruncateMilliseconds(TimeSpan.FromSeconds(1));     // Truncate to whole seconds
dateTime = dateTime.TruncateMilliseconds(TimeSpan.FromMinutes(1));    // Truncate to whole minutes
// ... and so on</code>

These methods provide straightforward ways to eliminate millisecond discrepancies when comparing DateTime objects, ensuring accurate timestamp comparisons.

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