Document SQL Server + triggers breaking change

Closes #3883

entity-framework/core/providers/sql-server/misc.md

@@ -0,0 +1,18 @@
+---
+title: Miscellaneous - Microsoft SQL Server Database Provider - EF Core
+description: Miscellaneous for the Microsoft SQL Server database provider
+author: roji
+ms.date: 06/07/2021
+uid: core/providers/sql-server/misc
+---
+# Miscellaneous notes for SQL Server
+
+## SaveChanges and database triggers
+
+Starting with EF Core 7.0, EF Core saves changes to the database with significantly optimized SQL; unfortunately, this technique is not supported on SQL Server if the target table has database triggers. For more information on this SQL Server limitation, see the documentation on the [OUTPUT clause](/sql/t-sql/queries/output-clause-transact-sql).
+
+You can let EF Core know that the target table has a trigger; doing so will revert to the previous, less efficient technique. This can be done by configuring the corresponding entity type as follows:
+
+[!code-csharp[Main](../../../../samples/core/SqlServer/Misc/TriggersContext.cs?name=TriggerConfiguration&highlight=4)]
+
+Note that doing this doesn't actually make EF Core create or manage the trigger in any way - it currently only informs EF Core that triggers are present on the table. As a result, any trigger name can be used.

entity-framework/core/what-is-new/ef-core-7.0/breaking-changes.md

@@ -9,3 +9,37 @@ uid: core/what-is-new/ef-core-7.0/breaking-changes
 # Breaking changes in EF Core 7.0
 
 API and behavior changes have the potential to break existing applications updating to EF Core 7.0.0 will be documented here.
+
+## Summary
+
+| **Breaking change**                                                                                          | **Impact**  |
+|:------------------------------------------------------------------------------------------------------------ | ----------- |
+| [SQL Server tables with triggers now require special EF Core configuration](#sqlserver-tables-with-triggers) | High        |
+
+## High-impact changes
+
+<a name="sqlserver-tables-with-triggers"></a>
+
+### SQL Server tables with triggers now require special EF Core configuration
+
+[Tracking Issue #27372](https://github.com/dotnet/efcore/issues/27372)
+
+#### Old behavior
+
+Previous versions of the SQL Server saved changes via a less efficient technique which always worked.
+
+#### New behavior
+
+By default, EF Core now saves changes via a significantly more efficient technique; unfortunately, this technique is not supported on SQL Server if the target table has database triggers.
+
+#### Why
+
+The performance improvements linked to the new method are significant enough that it's important to bring them to users by default. At the same time, we estimate usage of database triggers in EF Core applications to be low enough that the negative breaking change consequences are outweighed by the performance gain.
+
+#### Mitigations
+
+You can let EF Core know that the target table has a trigger; doing so will revert to the previous, less efficient technique. This can be done by configuring the corresponding entity type as follows:
+
+[!code-csharp[Main](../../../../samples/core/SqlServer/Misc/TriggersContext.cs?name=TriggerConfiguration&highlight=4)]
+
+Note that doing this doesn't actually make EF Core create or manage the trigger in any way - it currently only informs EF Core that triggers are present on the table. As a result, any trigger name can be used.

entity-framework/toc.yml

@@ -357,6 +357,8 @@
           href: core/providers/sql-server/spatial.md
         - name: Specify Azure SQL Database options
           href: core/providers/sql-server/azure-sql-database.md
+        - name: Miscellaneous
+          href: core/providers/sql-server/misc.md
       - name: SQLite
         items:
         - name: Overview

samples/core/SqlServer/Misc/Blog.cs

@@ -0,0 +1,7 @@
+namespace SqlServer.Faq;
+
+public class Blog
+{
+    public int BlogId { get; set; }
+    public string Url { get; set; }
+}

samples/core/SqlServer/Misc/TriggersContext.cs

@@ -0,0 +1,17 @@
+
+using Microsoft.EntityFrameworkCore;
+
+namespace SqlServer.Faq;
+
+public class TriggersContext : DbContext
+{
+    public DbSet<Blog> Blogs { get; set; }
+
+    #region TriggerConfiguration
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        modelBuilder.Entity<Blog>()
+            .ToTable(tb => tb.HasTrigger("SomeTrigger"));
+    }
+    #endregion
+}

samples/core/SqlServer/SqlServer.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="6.0.0" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0-preview.4.22229.2" />
   </ItemGroup>
 
 </Project>