fix: UTC dateTimes convertor (#266)

* - convert dateTime to UTC equivalent

* - support DateTimeKind.Local

* test: add datetime conversion tests

* test: rewrite datetime conversion tests to check with local timezone offsets

---------

Co-authored-by: Saulius Saltenis <[email protected]>

Author: saulius-saltenis-Devoteam

src/Gridify/Builder/BaseQueryBuilder.cs

@@ -204,7 +204,12 @@ private object AddIndexerNullCheck(LambdaExpression mapTarget, object query)
          {
             if (mapper.Configuration.DefaultDateTimeKind.HasValue)
             {
-               value = DateTime.SpecifyKind(dateTime, mapper.Configuration.DefaultDateTimeKind.Value);
+               value = mapper.Configuration.DefaultDateTimeKind.Value switch
+               {
+                  DateTimeKind.Local => dateTime.ToLocalTime(),
+                  DateTimeKind.Utc => dateTime.ToUniversalTime(),
+                  _ => dateTime
+               };
             }
          }
       }

test/EntityFrameworkPostgreSqlIntegrationTests/PR266Tests.cs

@@ -0,0 +1,61 @@
+using EntityFrameworkIntegrationTests.cs;
+using Gridify;
+using Microsoft.EntityFrameworkCore;
+using Xunit;
+
+namespace EntityFrameworkPostgreSqlIntegrationTests;
+
+public class PR266Tests
+{
+   private readonly MyDbContext _dbContext = new();
+
+   [Fact]
+   public void ISO_Should_Convert_ToUTC()
+   {
+      var isoTimestamp = "2025-03-31T02:54:09Z";
+
+      var mapper = new GridifyMapper<User>(q => q.DefaultDateTimeKind = DateTimeKind.Utc).GenerateMappings();
+      var queryString = _dbContext.Users.ApplyFiltering($"CreateDate={isoTimestamp}", mapper).ToQueryString();
+
+      var whereClause = queryString.Split("WHERE")[1].Trim();
+      Assert.Equal($"u.\"CreateDate\" = TIMESTAMPTZ '{isoTimestamp}'", whereClause);
+   }
+
+   [Fact]
+   public void ISO_Should_ShowcaseDifferentConversions_LocalToUtc()
+   {
+      var localOffset = TimeZoneInfo.Local.GetUtcOffset(DateTime.Now);
+
+      var localDt = DateTime.Parse("2025-03-31T02:54:09Z");
+      Assert.Equal(DateTimeKind.Local, localDt.Kind);
+
+      // Past behavior. Kind becomes Utc, but time is not converted.
+      var utcDtWrong = DateTime.SpecifyKind(localDt, DateTimeKind.Utc);
+      Assert.Equal(DateTimeKind.Utc, utcDtWrong.Kind);
+      Assert.Equal(localDt, utcDtWrong);
+
+      // Current behavior. Kind becomes Utc, and time is converted.
+      var utcDtCorrect = localDt.ToUniversalTime();
+      Assert.Equal(DateTimeKind.Utc, utcDtCorrect.Kind);
+      Assert.Equal(localDt.Subtract(localOffset), utcDtCorrect);
+   }
+
+   [Fact]
+   public void ISO_Should_ShowcaseDifferentConversions_UtcToLocal()
+   {
+      var localOffset = TimeZoneInfo.Local.GetUtcOffset(DateTime.Now);
+
+      var utcDt = DateTime.Parse("2025-03-31T02:54:09Z").ToUniversalTime();
+      Assert.Equal(DateTimeKind.Utc, utcDt.Kind);
+
+      // Past behavior. Kind becomes Local, but time is not converted.
+      var localDtWrong = DateTime.SpecifyKind(utcDt, DateTimeKind.Local);
+      Assert.Equal(DateTimeKind.Local, localDtWrong.Kind);
+      Assert.Equal(utcDt, localDtWrong);
+
+      // Current behavior. Kind becomes Local, and time is converted.
+      var localDtCorrect = utcDt.ToLocalTime();
+      Assert.Equal(DateTimeKind.Local, localDtCorrect.Kind);
+      Assert.Equal(utcDt.Add(localOffset), localDtCorrect);
+   }
+}