Breaking change note for DateOnly/TimeOnly scaffolding

Closes dotnet#4233

Author: roji

entity-framework/core/what-is-new/ef-core-8.0/breaking-changes.md

@@ -9,3 +9,54 @@ uid: core/what-is-new/ef-core-8.0/breaking-changes
 # Breaking changes in EF Core 8.0 (EF8)
 
 This page will dcoument API and behavior changes that have the potential to break existing applications updating to EF Core 8.0.
+
+## Summary
+
+| **Breaking change**                                                                                                                      | **Impact** |
+|:---------------------------------------------------------------------------------------------------------------------------------------- | ---------- |
+| [SQL Server `date` and `time` now scaffold to .NET `DateOnly` and `TimeOnly`](#sqlserver-date-time-only)                                 | Medium     |
+
+## Medium-impact changes
+
+<a name="sqlserver-date-time-only"></a>
+
+### SQL Server `date` and `time` now scaffold to .NET `DateOnly` and `TimeOnly`
+
+[Tracking Issue #24507](https://github.com/dotnet/efcore/issues/24507)
+
+#### Old behavior
+
+Previously, when scaffolding a SQL Server database with `date` or `time` columns, EF would generate entity properties with types [`DateTime`](https://learn.microsoft.com/dotnet/api/system.datetime) and [`TimeSpan`](https://learn.microsoft.com/dotnet/api/system.timespan).
+
+#### New behavior
+
+Starting with EF Core 8.0, `date` and `time` are scaffolded as [`DateOnly`](https://learn.microsoft.com/dotnet/api/system.dateonly) and [`TimeOnly`](https://learn.microsoft.com/dotnet/api/system.timeonly).
+
+#### Why
+
+`DateOnly` and `TimeOnly` were introduced in .NET 6.0, and are a perfect match for mapping the database date and time types. `DateTime` notably contains a time component that goes unused and can cause confusion when mapping it to `date`, and `TimeSpan` represents a time interval - possibly including days - rather than a time of day at which an event occurs. Using the new types prevents bugs and confusion, and provides clarity of intent.
+
+#### Mitigations
+
+This change only affects users which regularly re-scaffold their database into an EF code model ("database-first" flow).
+
+It is recommended to react to this change by modifying your code to use the newly scaffolded `DateOnly` and `TimeOnly` types. However, if that isn't possible, you can edit the scaffolding templates to revert to the previous mapping. To do this, set up the templates as described on [this page](xref:core/managing-schemas/scaffolding/templates). Then, edit the `EntityType.t4` file, find where the entity properties get generated (search for `property.ClrType`), and change the code to the following:
+
+```c#
+        var clrType = property.GetColumnType() switch
+        {
+            "date" when property.ClrType == typeof(DateOnly) => typeof(DateTime),
+            "date" when property.ClrType == typeof(DateOnly?) => typeof(DateTime?),
+            "time" when property.ClrType == typeof(TimeOnly) => typeof(TimeSpan),
+            "time" when property.ClrType == typeof(TimeOnly?) => typeof(TimeSpan?),
+            _ => property.ClrType
+        };
+
+        usings.AddRange(code.GetRequiredUsings(clrType));
+
+        var needsNullable = Options.UseNullableReferenceTypes && property.IsNullable && !clrType.IsValueType;
+        var needsInitializer = Options.UseNullableReferenceTypes && !property.IsNullable && !clrType.IsValueType;
+#>
+    public <#= code.Reference(clrType) #><#= needsNullable ? "?" : "" #> <#= property.Name #> { get; set; }<#= needsInitializer ? " = null!;" : "" #>
+<#
+```