Update TPC sample with Identity column code (#3990)

Author: ajcvickers

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

@@ -732,7 +732,17 @@ For databases that support sequences, key values can be generated by using a sin
 
 `AnimalSequence` is a database sequence created by EF Core. This strategy is used by default for TPC hierarchies when using the EF Core database provider for SQL Server. Database providers for other databases that support sequences should have a similar default. Other key generation strategies that use sequences, such as Hi-Lo patterns, may also be used with TPC.
 
-SQLite does not support sequences, and hence integer key value generation is not supported when using SQLite with the TPC strategy. However, client-side generation or globally unique keys--for example, GUID keys--are supported on any database, including SQLite.
+While standard Identity columns will not work with TPC, it is possible to use Identity columns if each table is configured with an appropriate seed and increment such that the values generated for each table will never conflict. For example:
+
+<!--
+            modelBuilder.Entity<Cat>().ToTable("Cats", tb => tb.Property(e => e.Id).UseIdentityColumn(1, 4));
+            modelBuilder.Entity<Dog>().ToTable("Dogs", tb => tb.Property(e => e.Id).UseIdentityColumn(2, 4));
+            modelBuilder.Entity<FarmAnimal>().ToTable("FarmAnimals", tb => tb.Property(e => e.Id).UseIdentityColumn(3, 4));
+            modelBuilder.Entity<Human>().ToTable("Humans", tb => tb.Property(e => e.Id).UseIdentityColumn(4, 4));
+-->
+[!code-csharp[UsingIdentity](../../../../samples/core/Miscellaneous/NewInEFCore7/TpcInheritanceSample.cs?name=UsingIdentity)]
+
+SQLite does not support sequences or Identity seed/increment, and hence integer key value generation is not supported when using SQLite with the TPC strategy. However, client-side generation or globally unique keys--for example, GUID keys--are supported on any database, including SQLite.
 
 ### Foreign key constraints
 

samples/core/Miscellaneous/NewInEFCore7/NewInEFCore7.csproj

@@ -9,13 +9,14 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="7.0.0-rc.1.22415.10" />
-    <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0-rc.1.22415.10" />
-    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0-rc.1.22415.10" />
-    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="7.0.0-rc.1.22415.10" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="7.0.0-rc.2.22420.3" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0-rc.2.22420.3" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0-rc.2.22420.3" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="7.0.0-rc.2.22420.3" />
   </ItemGroup>
 
   <ItemGroup>
+    <Using Include="System.ComponentModel.DataAnnotations" />
     <Using Include="System.ComponentModel.DataAnnotations.Schema" />
     <Using Include="System.Data.Common" />
     <Using Include="System.Linq.Expressions" />

samples/core/Miscellaneous/NewInEFCore7/Program.cs

@@ -8,9 +8,7 @@ public static async Task Main()
         await TpcInheritanceSample.Inheritance_with_TPT();
         await TpcInheritanceSample.Inheritance_with_TPC();
         await TpcInheritanceSample.Inheritance_with_TPC_using_HiLo();
-
-        // Currently not working: see https://github.com/dotnet/efcore/issues/28195
-        // await TpcInheritanceSample.Inheritance_with_TPC_using_Identity();
+        await TpcInheritanceSample.Inheritance_with_TPC_using_Identity();
 
         await ExecuteDeleteSample.ExecuteDelete();
         await ExecuteDeleteSample.ExecuteDeleteTpt();

samples/core/Miscellaneous/NewInEFCore7/TpcInheritanceSample.cs

@@ -374,13 +374,15 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
         {
             modelBuilder.Entity<Animal>().UseTpcMappingStrategy();
 
-            // Currently not working: see https://github.com/dotnet/efcore/issues/28195
-            modelBuilder.Entity<FarmAnimal>().Property(e => e.Id).ValueGeneratedOnAdd().UseIdentityColumn(1, 4);
-            modelBuilder.Entity<Cat>().Property(e => e.Id).ValueGeneratedOnAdd().UseIdentityColumn(2, 4);
-            modelBuilder.Entity<Dog>().Property(e => e.Id).ValueGeneratedOnAdd().UseIdentityColumn(3, 4);
-            modelBuilder.Entity<Human>().Property(e => e.Id).ValueGeneratedOnAdd().UseIdentityColumn(4, 4);
+            #region UsingIdentity
+            modelBuilder.Entity<Cat>().ToTable("Cats", tb => tb.Property(e => e.Id).UseIdentityColumn(1, 4));
+            modelBuilder.Entity<Dog>().ToTable("Dogs", tb => tb.Property(e => e.Id).UseIdentityColumn(2, 4));
+            modelBuilder.Entity<FarmAnimal>().ToTable("FarmAnimals", tb => tb.Property(e => e.Id).UseIdentityColumn(3, 4));
+            modelBuilder.Entity<Human>().ToTable("Humans", tb => tb.Property(e => e.Id).UseIdentityColumn(4, 4));
+            #endregion
 
             modelBuilder.Entity<Food>().UseTpcMappingStrategy();
+
             base.OnModelCreating(modelBuilder);
         }
     }