Generate temp values for key properties contained in optional FKs

Fixes #27455

src/EFCore/ChangeTracking/Internal/InternalEntityEntry.cs

@@ -1459,6 +1459,9 @@ public void AcceptChanges()
  }
  }
 
+ private readonly static bool _useOldBehavior27455 =
+ AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue27455", out var enabled27455) && enabled27455;
+
  /// <summary>
  /// This is an internal API that supports the Entity Framework Core infrastructure and not subject to
  /// the same compatibility standards as public APIs. It may be changed or removed without notice in
@@ -1485,7 +1488,8 @@ public InternalEntityEntry PrepareToSave()
 
  if (property.IsKey()
  && property.IsForeignKey()
- && _stateData.IsPropertyFlagged(property.GetIndex(), PropertyFlag.Unknown))
+ && _stateData.IsPropertyFlagged(property.GetIndex(), PropertyFlag.Unknown)
+ && (_useOldBehavior27455 || !IsStoreGenerated(property)))
  {
  throw new InvalidOperationException(CoreStrings.UnknownKeyValue(entityType.DisplayName(), property.Name));
  }

src/EFCore/Metadata/Internal/PropertyExtensions.cs

@@ -1,7 +1,9 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Collections.Generic;
+using System.Linq;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Utilities;
 
@@ -74,6 +76,9 @@ public static bool ForUpdate(this ValueGenerated valueGenerated)
  return null;
  }
 
+ private readonly static bool _useOldBehavior27455 =
+ AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue27455", out var enabled27455) && enabled27455;
+
  /// <summary>
  /// This is an internal API that supports the Entity Framework Core infrastructure and not subject to
  /// the same compatibility standards as public APIs. It may be changed or removed without notice in
@@ -83,7 +88,10 @@ public static bool ForUpdate(this ValueGenerated valueGenerated)
  public static bool RequiresValueGenerator(this IReadOnlyProperty property)
  => (property.ValueGenerated.ForAdd()
  && property.IsKey()
- && (!property.IsForeignKey() || property.IsForeignKeyToSelf()))
+ && (!property.IsForeignKey()
+ || property.IsForeignKeyToSelf()
+ || (!_useOldBehavior27455
+ && property.GetContainingForeignKeys().All(fk => fk.Properties.Any(p => p != property && p.IsNullable)))))
  || property.GetValueGeneratorFactory() != null;
 
  /// <summary>

test/EFCore.Specification.Tests/StoreGeneratedTestBase.cs

@@ -512,6 +512,45 @@ public virtual void Identity_property_on_Added_entity_with_temporary_value_gets_
  context => Assert.Equal("Banana Joe", context.Set<Gumball>().Single(e => e.Id == id).Identity));
  }
 
+#nullable enable
+ protected class CompositePrincipal
+ {
+ public int Id { get; set; }
+ public int? CurrentNumber { get; set; }
+ public CompositeDependent? Current { get; set; }
+ public ICollection<CompositeDependent> Periods { get; } = new HashSet<CompositeDependent>();
+ }
+
+ protected class CompositeDependent
+ {
+ public int PrincipalId { get; set; }
+ public int Number { get; set; }
+ public CompositePrincipal? Principal { get; set; }
+ }
+#nullable disable
+
+ [ConditionalFact]
+ public virtual void Store_generated_values_are_propagated_with_composite_key_cycles()
+ {
+ var id = 0;
+
+ ExecuteWithStrategyInTransaction(
+ context =>
+ {
+ var period = new CompositeDependent
+ {
+ Number = 1,
+ Principal = new CompositePrincipal()
+ };
+
+ context.Add(period);
+ context.SaveChanges();
+
+ id = period.PrincipalId;
+ },
+ context => Assert.Equal(1, context.Set<CompositeDependent>().Single(e => e.PrincipalId == id).Number));
+ }
+
  protected class NonStoreGenDependent
  {
  [DatabaseGenerated(DatabaseGeneratedOption.None)]
@@ -1947,10 +1986,30 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
  modelBuilder.Entity<OptionalProduct>();
  modelBuilder.Entity<StoreGenPrincipal>();
 
- modelBuilder.Entity<NonStoreGenDependent>()
- .Property(e => e.HasTemp)
- .ValueGeneratedOnAddOrUpdate()
- .HasValueGenerator<TemporaryIntValueGenerator>();
+ modelBuilder.Entity<NonStoreGenDependent>(eb =>
+ {
+ eb.Property(e => e.HasTemp)
+ .ValueGeneratedOnAddOrUpdate()
+ .HasValueGenerator<TemporaryIntValueGenerator>();
+ });
+
+ modelBuilder.Entity<CompositePrincipal>(entity =>
+ {
+ entity.HasKey(x => x.Id);
+ entity.Property(x => x.Id)
+ .ValueGeneratedOnAdd();
+ entity.HasOne(x => x.Current)
+ .WithOne()
+ .HasForeignKey<CompositePrincipal>(x => new { x.Id, x.CurrentNumber });
+ });
+
+ modelBuilder.Entity<CompositeDependent>(entity =>
+ {
+ entity.HasKey(x => new { x.PrincipalId, x.Number });
+ entity.HasOne(x => x.Principal)
+ .WithMany(x => x.Periods)
+ .HasForeignKey(x => x.PrincipalId);
+ });
  }
  }
  }

test/EFCore.SqlServer.FunctionalTests/StoreGeneratedSqlServerTest.cs

@@ -228,6 +228,8 @@ protected override void OnModelCreating(ModelBuilder modelBuilder, DbContext con
 
  modelBuilder.Entity<NonStoreGenDependent>().Property(e => e.HasTemp).HasDefaultValue(777);
 
+ modelBuilder.Entity<CompositePrincipal>().Property(e => e.Id).UseIdentityColumn();
+
  base.OnModelCreating(modelBuilder, context);
  }
  }