How to add multiple entity with childs at once

Question

I'm having trouble adding multiple entities with multiple children at once in foreach loop.
Its obvious ef cannot track ids in foreach loop. But maybe there are other solutions that you can guide me.

The error when I tried to add multiple entities with a child is:

The instance of entity type cannot be tracked because of another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.

For example:

public class Order
{
    public Order()
    {
        OrderDetails = new HashSet<OrderDetail>();
    }

    [Key]
    public int Id { get; set; }

    [StringLength(50)]
    public string Code { get; set; }

    public int? CompanyId { get; set; }
    public int? PartnerId { get; set; }
    public decimal TotalNetPrice { get; set; }
    public decimal TotalPrice { get; set; } 
    public bool IsActive { get; set; } = true;
    public bool IsDeleted { get; set; } = false;

    [ForeignKey("CompanyId")]
    public virtual Company Company { get; set; }

    [ForeignKey("PartnerId")]
    public virtual Partner Partner { get; set; }

    public virtual ICollection<OrderDetail> OrderDetails { get; set; }
}

public class OrderDetail
{

    [Key]
    public int Id { get; set; }

    public int OrderId { get; set; }

    [StringLength(50)]
    public string Code { get; set; }

    public int LineNumber { get; set; }
    public int ProductId { get; set; }
    public int Quantity { get; set; }
    public bool IsActive { get; set; } = true;
    public bool IsDeleted { get; set; } = false;

    [ForeignKey("OrderId")]
    public virtual Order Order { get; set; }

    [ForeignKey("ProductId")]
    public virtual Product Product { get; set; }
}

Here is my code in the method:

foreach (var order in orderList)
{
    // consider we create/cast object to Order class.
    _orderService.Add(order);
    // in here we don't have id, because we didn't call savechanges.

    foreach(var orderDetail in order.orderDetailList)
    {
        // consider we create/cast object to OrderDetail class.
        orderDetail.orderId = order.Id;
        // in here, order id is always 0 as expected.
        _order.OrderDetails.Add(orderDetail);
    }
}

try 
{
    await uow.SaveChangesAsync();
}
catch(Exception exception)
{
    var msg = exception.Message;
}

I tried to use [DatabaseGenerated(DatabaseGeneratedOption.Identity)] attribute for the identity columns.

According to documentation (https://learn.microsoft.com/en-us/ef/core/modeling/generated-properties?tabs=data-annotations):

Depending on the database provider being used, values may be generated client side by EF or in the database. If the value is generated by the database, then EF may assign a temporary value when you add the entity to the context. This temporary value will then be replaced by the database generated value during SaveChanges().

So it should give at least temp id to track it. But it didn't work with my case.
I also tried the same approach on model creating a part in context. But again the same result. No success.

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Entity>()
        .Property(x => x.Id)
        .ValueGeneratedOnAdd();
}

It seems like the best solution is to make a transaction and save order before details and get real id and then add details. But it has performance issues as you know.
I'm wondering if there is any other best practice for that issue?
Thank you.

Answer 1

Try this:

foreach (var order in orderList)
{
    _orderService.Add(order);

    foreach(var orderDetail in order.orderDetailList)
    {
        // Add reference Of Order to OrderDetails, not an id
        orderDetail.Order = order;
        _order.OrderDetails.Add(orderDetail);
    }
}

In this case EF will know how to connect Order and OrderDetail on SaveChangesAsync