[release/11.0] Allow unconstrained relationships to break SaveChanges command cycles

src/EFCore.Relational/Update/Internal/CommandBatchPreparer.cs

@@ -1078,7 +1078,11 @@ private void AddMatchingPredecessorEdge<T>(
                     }
 
                     AfterLoop:
-                    _modificationCommandGraph.AddEdge(predecessor, command, new CommandDependency(foreignKey), requiresBatchingBoundary);
+                    _modificationCommandGraph.AddEdge(
+                        predecessor,
+                        command,
+                        new CommandDependency(foreignKey, Breakable: !foreignKey.IsConstrained && !requiresBatchingBoundary),
+                        requiresBatchingBoundary);
                 }
             }
         }

test/EFCore.Relational.Tests/Update/CommandBatchPreparerTest.cs

@@ -449,6 +449,50 @@ public void Batch_command_throws_on_commands_with_circular_dependencies(bool sen
                 .Message);
     }
 
+    [Fact]
+    public void Batch_command_breaks_cycle_for_unconstrained_foreign_key()
+    {
+        var model = CreateCyclicFKModel(unconstrained: true);
+        var configuration = CreateContextServices(model);
+        var stateManager = configuration.GetRequiredService<IStateManager>();
+
+        var fakeEntry = stateManager.GetOrCreateEntry(
+            new FakeEntity { RelatedId = 1 });
+        fakeEntry.SetEntityState(EntityState.Added);
+
+        var temporaryIdValue = fakeEntry.GetCurrentValue<int>(fakeEntry.EntityType.GetProperty(nameof(FakeEntity.Id)));
+        var relatedFakeEntry = stateManager.GetOrCreateEntry(
+            new RelatedFakeEntity { Id = 1, RelatedId = temporaryIdValue });
+        relatedFakeEntry.SetEntityState(EntityState.Added);
+
+        var batches = CreateBatches([relatedFakeEntry, fakeEntry], new UpdateAdapter(stateManager));
+
+        Assert.Collection(
+            batches,
+            b => Assert.Same(fakeEntry, b.ModificationCommands.Single().Entries.Single()),
+            b => Assert.Same(relatedFakeEntry, b.ModificationCommands.Single().Entries.Single()));
+    }
+
+    [Fact]
+    public void Batch_command_does_not_break_cycle_for_unconstrained_foreign_key_with_store_generated_principal_key()
+    {
+        var model = CreateCyclicFKModel(unconstrainedPrincipalGenerated: true);
+        var configuration = CreateContextServices(model);
+        var stateManager = configuration.GetRequiredService<IStateManager>();
+
+        var fakeEntry = stateManager.GetOrCreateEntry(
+            new FakeEntity { RelatedId = 1 });
+        fakeEntry.SetEntityState(EntityState.Added);
+
+        var temporaryIdValue = fakeEntry.GetCurrentValue<int>(fakeEntry.EntityType.GetProperty(nameof(FakeEntity.Id)));
+        var relatedFakeEntry = stateManager.GetOrCreateEntry(
+            new RelatedFakeEntity { Id = 1, RelatedId = temporaryIdValue });
+        relatedFakeEntry.SetEntityState(EntityState.Added);
+
+        Assert.Throws<InvalidOperationException>(
+            () => CreateBatches([fakeEntry, relatedFakeEntry], new UpdateAdapter(stateManager)));
+    }
+
     [InlineData(true), InlineData(false), Theory]
     public void Batch_command_throws_on_commands_with_circular_dependencies_including_indexes(bool sensitiveLogging)
     {
@@ -1083,7 +1127,7 @@ private static IModel CreateFKOneToManyModelWithGeneratedIds()
         return modelBuilder.Model.FinalizeModel();
     }
 
-    private static IModel CreateCyclicFKModel()
+    private static IModel CreateCyclicFKModel(bool unconstrained = false, bool unconstrainedPrincipalGenerated = false)
     {
         var modelBuilder = FakeRelationalTestHelpers.Instance.CreateConventionBuilder();
 
@@ -1093,16 +1137,34 @@ private static IModel CreateCyclicFKModel()
             b.HasIndex(c => c.UniqueValue).IsUnique();
         });
 
-        modelBuilder.Entity<RelatedFakeEntity>(b => b.HasOne<FakeEntity>()
-            .WithOne()
-            .HasForeignKey<RelatedFakeEntity>(c => c.RelatedId));
+        modelBuilder.Entity<RelatedFakeEntity>(b =>
+        {
+            var foreignKeyBuilder = b.HasOne<FakeEntity>()
+                .WithOne()
+                .HasForeignKey<RelatedFakeEntity>(c => c.RelatedId);
 
-        modelBuilder
+            if (unconstrainedPrincipalGenerated)
+            {
+                foreignKeyBuilder.IsConstrained(false);
+            }
+
+            if (unconstrained || unconstrainedPrincipalGenerated)
+            {
+                b.Property(c => c.Id).ValueGeneratedNever();
+            }
+        });
+
+        var foreignKeyBuilder = modelBuilder
             .Entity<FakeEntity>()
             .HasOne<RelatedFakeEntity>()
             .WithOne()
             .HasForeignKey<FakeEntity>(c => c.RelatedId);
 
+        if (unconstrained)
+        {
+            foreignKeyBuilder.IsConstrained(false);
+        }
+
         return modelBuilder.Model.FinalizeModel();
     }