Migrating EF6 app to EFCore 10 -- Stange bug ??

[LstpierreMaximum]

Question

I'm migrating an EF6 app to a SQL Server and a net 10 ef core

I got a table (Configuration) that contains only 1 records for all configuration of the application
I got a table (FiscalPeriod) that contains all Fiscal Periods of the company

In the tale FiscalPeriod, I got an Id (int), serveral dates..

In the configuration table, I got an Id (UniqueIdentifier) and a one CurrentFiscalId (FK to table FiscalPeriod)
the CurrentFiscalId is not nullable

In the Configuration class, I got the Navigation CurrentFiscal (FiscalPeriod) and the CurrentFiscalId property (int).
In the FiscalPeriod class, I don't have Navigation Property to Configuration

Everythings work fine, I can Add FiscalPeriod and configurationig data in context and save..

But when i want to "change" the current FiscalId to an existing one (ex: pass 3 to 2)
I got an error

"The association between entities 'FiscalPeriod' and 'Configuration' with the key value '{CurrentPeriodYearId: 3}'
has been severed, but the relationship is either marked as required or is implicitly required because the foreign key is not nullable.
If the dependent/child entity should be deleted when a required relationship is severed, configure the relationship to use cascade deletes."

I don't want to delete the row in "FiscalPeriod" only change the link in the Configuration table

I did try serveral thing the the builder

Any Ideas ????

Your code

modelBuilder.Entity<Configuration>(entity =>
{
    entity.ToTable("Configuration"), 
       tb =>tb.HasTrigger("Trigger_Configuration_ProfitCenterUnitDescription"));

    entity.HasKey(e => e.UniqueId);

    entity.Property(e => e.CurrentPeriodYearId).IsRequired();

    // did try .. WithMany and other ...
    entity.HasOne(e => e.CurrentPeriodYear)
	 .WithOne()
	 .HasForeignKey<Configuration>(e => e.CurrentPeriodYearId)
	 .HasPrincipalKey<FiscalPeriod>(e => e.PeriodId)
	 .IsRequired(false)
	 .HasConstraintName("FK_Configuration_FiscalPeriod");
		 
	...
}
modelBuilder.Entity<FiscalPeriod>(entity =>
{
    entity.ToTable("FiscalPeriod);
      
    entity.HasKey(e => e.PeriodId);
    ...
}

Stack traces

fail: 2025-12-10 16:50:58.088 CoreEventId.SaveChangesFailed[10000] (Microsoft.EntityFrameworkCore.Update) 
      An exception occurred in the database while saving changes for context type 'Maximum.Edm.MaximumEntitiesContext'.
      System.InvalidOperationException: The association between entities 'FiscalPeriod' and 'AccountingConfiguration' with the key value '{CurrentPeriodYearId: 3}' has been severed, but the relationship is either marked as required or is implicitly required because the foreign key is not nullable. If the dependent/child entity should be deleted when a required relationship is severed, configure the relationship to use cascade deletes.
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.HandleConceptualNulls(Boolean sensitiveLoggingEnabled, Boolean force, Boolean isCascadeDelete)
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.CascadeChanges(Boolean force)
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.GetEntriesToSave(Boolean cascadeChanges)
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChanges(StateManager stateManager, Boolean acceptAllChangesOnSuccess)
         at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func`3 operation, Func`3 verifySucceeded)
         at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)

Verbose output

EF Core version

10.0

Database provider

No response

Target framework

net 10

Operating system

No response

IDE

studio 2026

[roji]

@LstpierreMaximum I'm going to need to see a minimal repro that shows what you're actually doing; a textual description and a partial snippet - as above - is very rarely enough for us to understand what you're doing and investigate.

Please put together a minimal console program that reproduces the error and we'll investigate.

[LstpierreMaximum]

@roji
I have created a small project
and do not have the issue

I will investigate..