The property 'InventoryItemID' is part of the object's key information and cannot be modified

Question

I can't add a new instance of the type InventoryItem because ChangeTracker thinks I modified the primary key. But it is as the constructor done.

On the other hand, I could add items without problem. But when I inserted it after creation of an InventoryItemType (that is a NavigationProperty of InventoryItem) it fails.

I searched, tried, updated EF from 5 to 6.1.1 and I surrended... I need your help

        InventoryItemType iit = new InventoryItemType
        {
            InventoryFamilyID = 12,
            Name = checkInPackage.Name,
            Provider = shippingDestination.RelatedWarehouse.Name,
            Reference = "Paquete nº " + checkInPackage.CheckInPackageId
        };


        this.inventoryItemTypeRepository.InsertOrUpdate(iit);
        this.inventoryItemTypeRepository.Save();

        InventoryItem ii = new InventoryItem
        {
            WarehouseID = checkInPackage.WarehouseID,
            Price = 0,
            InventoryItemTypeID = iit.InventoryItemTypeID
        };


        this.inventoryItemRepository.InsertOrUpdate(ii); // th
        this.inventoryItemRepository.Save();

The repository has:

    public void InsertOrUpdate(InventoryItem inventoryitem)
    {
        if (inventoryitem.InventoryItemID == default(int)) {
            // New entity
            context.InventoryItems.Add(inventoryitem);
        } else {
            // Existing entity
            context.Entry(inventoryitem).State = EntityState.Modified;
        }
    }

EDITED WITH THE FIX:

I had a bad definition about the relationship InventoryItemType 1 to InventoryItem n

After doing this changes in InventoryItemType.cs it runs without errors:

    public InventoryItemType()
    {
        InventoryItems = new HashSet<InventoryItem>();
    }
    public virtual ICollection<InventoryItem> InventoryItems { get; set; } 

In business logic side

    iit.InventoryItems.Add(
            new InventoryItem
            {
                WarehouseID = checkInPackage.WarehouseID,
                Price = 0,
                InventoryItemType = iit
            }
    );

    this.inventoryItemTypeRepository.InsertOrUpdate(iit);
    this.inventoryItemTypeRepository.Save();

Answer 1

According to this description and this one, Instead of setting InventoryItemTypeID set InventoryItemType in InventoryItem entity, maybe it works.

InventoryItem ii = new InventoryItem
{
    WarehouseID = checkInPackage.WarehouseID,
    Price = 0,
    InventoryItemType = iit
};