EF Core DDD ValueObject property is part of a key and so cannot be modified or marked as modified

Question

Hello I sometimes have in parallel integration tests problem with saving entities. EF Core throws exception with message: The property 'Order.Price#Money.OrderId' is part of a key and so cannot be modified or marked as modified.

It is really curious that I run single test 'should_get_order' and everything is fine, but when I try to run all tests sometimes I have issue

Here is implementation

public class Order : AggregateRoot
{
    // some other props
    public Money Price { get; private set; }

    public Order() 
    {
        Price = Money.Zero; // exception throws but when I change to new Money(0) everything works fine
    }

    public static Order Create() 
    {
        return new Order();
    }
}

public abstract class AggregateRoot
{
    public AggregateId Id { get; protected set; }
}

public class AggregateId<T> : IEquatable<AggregateId<T>>
{
    public T Value { get; }

    public AggregateId(T value)
    {
        Value = value;
    }

    public bool Equals(AggregateId<T>? other)
    {
        if (ReferenceEquals(null, other)) return false;
        if (ReferenceEquals(this, other)) return true;
        return EqualityComparer<T>.Default.Equals(Value, other.Value);
    }

    public override bool Equals(object? obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != this.GetType()) return false;
        return Equals((AggregateId<T>)obj);
    }

    public override int GetHashCode()
    {
        return EqualityComparer<T>.Default.GetHashCode(Value);
    }
}

public class AggregateId : AggregateId<Guid>
{
    public AggregateId() : this(Guid.NewGuid())
    {
    }

    public AggregateId(Guid value) : base(value)
    {
    }

    public static implicit operator Guid(AggregateId id) => id.Value;
    public static implicit operator AggregateId(Guid id) => new(id);
}

public class Money : IEquatable<Money>
{
    public static readonly Money Zero = new Money(0);
    public decimal Value { get; }

    public Money(decimal value)
    {
        if (value < 0)
        {
            throw new InvalidOperationException($"Money '{value}' cannot be negative");
        }

        Value = value;
    }

    public Money ChangeValue(decimal value)
    {
        return new Money(value);
    }

    public bool Equals(Money? other)
    {
        if (other is null) return false;
        if (ReferenceEquals(null, other)) return false;
        if (ReferenceEquals(this, other)) return true;
        return Value == other.Value;
    }

    public override bool Equals(object? obj)
    {
        if (obj as Money is null) return false;
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != GetType()) return false;
        return Equals((Money)obj);
    }

    public override int GetHashCode()
    {
        return EqualityComparer<decimal>.Default.GetHashCode(Value);
    }

    public override string ToString()
    {
        return Value.ToString("0.00", CultureInfo.CreateSpecificCulture("en-US"));
    }
}

Configuration

internal class OrderConfiguration : IEntityTypeConfiguration<Order>
{
    public void Configure(EntityTypeBuilder<Order> builder)
    {
        builder.HasKey(o => o.Id);

        builder
            .Property(o => o.Id)
            .HasConversion(id => id.Value, id => new AggregateId(id));

        builder.OwnsOne(i => i.Price, navigation =>
        {
            navigation.Property(m => m.Value).HasColumnName("Cost").IsRequired().HasPrecision(14, 4);
        });
    }
}

Integration test

public class OrdersTests : IClassFixture<TestApplicationFactory<Program>>,
    IClassFixture<TestDbContext>
{
    [Fact]
    public async Task should_get_order()
    {
        var order = Order.Create();
        await _dbContext.AddAsync(order); // here there are some exceptions
        await _dbContext.SaveChangesAsync();
        
        var response = await _client.Request($"{Path}/{order.Id.Value}").GetAsync();
        var order = await response.GetJsonAsync<Order>();

        order.ShouldNotBeNull();
    }

    // some other tests
}

public class TestApplicationFactory<TProgram> : WebApplicationFactory<TProgram> where TProgram : class
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.UseEnvironment("test");
    }
}

public class TestDbContext : IDisposable
{
    internal OrderDbContext DbContext { get; }

    private const string AppSettings = "appsettings.test.json";

    private static readonly IConfiguration Configuration =  new ConfigurationBuilder().AddJsonFile(AppSettings)
                                                      .AddEnvironmentVariables()
                                                      .Build();

    public TestDbContext()
    {
        DbContext = new OrderDbContext(new DbContextOptionsBuilder<OrderDbContext>().UseNpgsql(Configuration["database:connectionString"])
                                    .EnableSensitiveDataLogging()
                                    .Options);
    }

    public void Dispose()
    {
        DbContext?.Database.EnsureDeleted();
        DbContext?.Dispose();
    }
}

When I change Price to new Money(0) there is no exceptions. Maybe the problem is in public static readonly field?

Message:

System.InvalidOperationException : The property 'Order.Price#Money.OrderId' is part of a key and so cannot be modified or marked as modified. To change the principal of an existing entity with an identifying foreign key, first delete the dependent and invoke 'SaveChanges', and then associate the dependent with the new principal.

Stack Trace:

    InternalEntityEntry.SetPropertyModified(IProperty property, Boolean changeState, Boolean isModified, Boolean isConceptualNull, Boolean acceptChanges)
ChangeDetector.PropertyChanged(InternalEntityEntry entry, IPropertyBase propertyBase, Boolean setModified)
InternalEntityEntryNotifier.PropertyChanged(InternalEntityEntry entry, IPropertyBase property, Boolean setModified)
InternalEntityEntry.SetProperty(IPropertyBase propertyBase, Object value, Boolean isMaterialization, Boolean setModified, Boolean isCascadeDelete, CurrentValueType valueType)
InternalEntityEntry.SetProperty(IPropertyBase propertyBase, Object value, Boolean isMaterialization, Boolean setModified, Boolean isCascadeDelete)
InternalEntityEntry.PropagateValue(InternalEntityEntry principalEntry, IProperty principalProperty, IProperty dependentProperty, Boolean isMaterialization, Boolean setModified)
NavigationFixer.SetForeignKeyProperties(InternalEntityEntry dependentEntry, InternalEntityEntry principalEntry, IForeignKey foreignKey, Boolean setModified, Boolean fromQuery)
NavigationFixer.InitialFixup(InternalEntityEntry entry, Boolean fromQuery)
NavigationFixer.StateChanged(InternalEntityEntry entry, EntityState oldState, Boolean fromQuery)
InternalEntityEntryNotifier.StateChanged(InternalEntityEntry entry, EntityState oldState, Boolean fromQuery)
InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges, Boolean modifyProperties)
InternalEntityEntry.SetEntityState(EntityState entityState, Boolean acceptChanges, Boolean modifyProperties, Nullable`1 forceStateWhenUnknownKey)
EntityGraphAttacher.PaintAction(EntityEntryGraphNode`1 node)
EntityEntryGraphIterator.TraverseGraph[TState](EntityEntryGraphNode`1 node, Func`2 handleNode)
EntityGraphAttacher.AttachGraph(InternalEntityEntry rootEntry, EntityState targetState, EntityState storeGeneratedWithKeySetTargetState, Boolean forceStateWhenUnknownKey)
DbContext.SetEntityState(InternalEntityEntry entry, EntityState entityState)
DbContext.SetEntityState[TEntity](TEntity entity, EntityState entityState)
DbContext.Add[TEntity](TEntity entity)
OrdersControllerTests.given_valid_order_item_should_add_to_order() line 24
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