List of items relate to two tables one contain foreign key other the primary key and check if item contain primary key is not in the database insert - asp.net

Question

I have task to get list of items which contain properties related to two tables(Item, PurchaseItemOrder), This list contain the Code property related to Item class this property is not the primary key for business reasons. So I have to search in the database by this Code and if this Item does not exist in the database insert it, And finally return the Id of the Item which is the primary key and get this key as foreign key in another table PurchaseItemOrder, I did some code, and I see this question Check if List of Items exist in database and if not Add it to database, but seems not exactly what I want can I do better?
Here May Code look like:
public class Item :Entity<int> , IFullAudited<User>
{
public string Name_en { get; set; }
public string Name_ar { get; set; }
public string Code { get; set; }
public string Description_en { get; set; }
public string Description_ar { get; set; }
public User CreatorUser { get; set; }
public User LastModifierUser { get; set; }
public long? CreatorUserId { get; set; }
public DateTime CreationTime { get; set; }
public long? LastModifierUserId { get; set; }
public DateTime? LastModificationTime { get; set; }
public User DeleterUser { get; set; }
public long? DeleterUserId { get; set; }
public DateTime? DeletionTime { get; set; }
public bool IsDeleted { get; set; }
}
public class PurchaseOrderItem : Entity<int>, IFullAudited<User>
{
public int POId { get; set; }
public int Qty { get; set; }
public int ItemId { get; set; }
public virtual Item Item { get; set; }
public User CreatorUser { get; set; }
public User LastModifierUser { get; set; }
public long? CreatorUserId { get; set; }
public DateTime CreationTime { get; set; }
public long? LastModifierUserId { get; set; }
public DateTime? LastModificationTime { get; set; }
public User DeleterUser { get; set; }
public long? DeleterUserId { get; set; }
public DateTime? DeletionTime { get; set; }
public bool IsDeleted { get; set; }
public PurchaseOrder PurchaseOrder { get; set; }
}
public class PurchaseOrderItemDto : EntityDto<int>
{
public string PONumber { get; set; }
public List<ItemDto> Items { get; set; }
}
public class ItemDto :EntityDto<int>
{
public string Name_en { get; set; }
public string Name_ar { get; set; }
public string Code { get; set; }
public string Description_en { get; set; }
public string Description_ar { get; set; }
public int Qty { get; set; }
}
private int CheckPO(PurchaseOrderItemDto dto)
{
var poExist = _purchaseOrderRepository.FirstOrDefault(po => po.PONumber == dto.PONumber);
int id;
if (poExist == null)
{
id = _purchaseOrderRepository.InsertAndGetId(new PurchaseOrder
{
PONumber = dto.PONumber,
StatusId = 1
});
}
else
{
id = poExist.Id;
}
return id;
}
private int CheckItem(ItemDto itemDto)
{
var itemExist = _itemRepository.FirstOrDefault(it => it.Code == itemDto.Code);
int id;
if (itemExist == null)
{
id = _itemRepository.InsertAndGetId(new Item
{
Name_en = itemDto.Name_en,
Name_ar = itemDto.Name_en,
Code = itemDto.Code,
Description_en = itemDto.Description_en,
Description_ar = itemDto.Description_ar
});
}
else
{
id = itemExist.Id;
}
return id;
}
public void UploadPurchaseOrderItems(PurchaseOrderItemDto dto)
{
var poId = CheckPO(dto);
foreach (var poItem in dto.Items)
{
int itemId = CheckItem(poItem);
_repository.Insert(new PurchaseOrderItem
{
POId = poId,
Qty = poItem.Qty,
ItemId = itemId
});
}
}