There are two relationships between the entities “ExpertSystem” and “ExpertiseVariable”. The expert system has many variables of expertise, but it also has a relationship with one of the variables of expertise to indicate that this variable is the target. But when I try to save the expert system to the database, I get an error:

System.InvalidOperationException: “Unable to save changes because a circular dependency was detected in the data to be saved: ‘ExpertSystem [Added] <-
ForeignKeyConstraint { ‘ExpertSystemId’ } ExpertiseVariable [Added] <-
ForeignKeyConstraint { ‘GoalVariableId’ } ExpertSystem [Added]To show additional information call ‘DbContextOptionsBuilder.EnableSensitiveDataLogging’.’.”

public class ExpertSystem
{
    public int Id { get; set; }

    public string Name { get; set; } = string.Empty;

    public List<ExpertiseVariable> ExpertiseVariables { get; set; } = new List<ExpertiseVariable>();

    public List<EnvironmentVariable> EnvironmentVariables { get; set; } = new List<EnvironmentVariable>();

    public InitializationBlock InitializationBlock { get; set; }

    public ExpertiseVariable GoalVariable { get; set; }

    public int? GoalVariableId { get; set; }

    public CompletionBlock CompletionBlock { get; set; }

    public List<VariableBlock> VariableBlocks { get; set; } = new List<VariableBlock>();
}

public class ExpertiseVariable
{
    public int Id { get; set; }

    public string Name { get; set; } = string.Empty;

    public ExpertSystem ExpertSystem { get; set; }

    public int ExpertSystemId { get; set; }

    public VariableBlock VariableBlock { get; set; }
}

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<ExpertSystem>()
        .HasMany(x => x.ExpertiseVariables)
        .WithOne(x => x.ExpertSystem)
        .HasForeignKey(x => x.ExpertSystemId);
    
    modelBuilder.Entity<ExpertSystem>()
        .HasOne(x => x.GoalVariable)
        .WithOne()
        .HasForeignKey<ExpertSystem>(x => x.GoalVariableId)
        .OnDelete(DeleteBehavior.Restrict);

    modelBuilder.Entity<ExpertiseVariable>()
        .HasOne(x => x.ExpertSystem)
        .WithMany(x => x.ExpertiseVariables)
        .HasForeignKey(x => x.ExpertSystemId)
        .OnDelete(DeleteBehavior.Cascade);
}