创建通用方法

Question

我正在尝试为以下代码创建一个通用方法：

foreach (var glitter in glitterpurchase.GlitterPurchaseDetails)
{
    var glitterInventory = _db.GlitterInventoriesRepository.GetAll(m => m.GlitterId == glitter.GlitterId);
    if (!glitterInventory.Any())
    {
        var newInventory = new GlitterInventory
        {
            GlitterId = glitter.GlitterId,
            Quantity = glitter.Quantity,
            TotalAmount = (decimal)glitter.Quantity * glitter.UnitPrice,
            UnitPrice = glitter.UnitPrice,
            CreatedBy = User.Identity.Name,
            CreatedDate = DateTime.Now,
        };
        _db.GlitterInventoriesRepository.Insert(newInventory);
    }
    else                    
    {
        var updateInventory = glitterInventory.First();
        updateInventory.Quantity += glitter.Quantity;
        updateInventory.TotalAmount += (decimal)glitter.Quantity * glitter.UnitPrice;
        updateInventory.UnitPrice = (decimal)updateInventory.Quantity / updateInventory.TotalAmount;
        updateInventory.UpdatedBy = User.Identity.Name;
        updateInventory.UpdatedDate = DateTime.Now;
        _db.GlitterInventoriesRepository.Update(updateInventory);
    }
}

上面的代码只是简单地更新了库存。我想制作一个通用方法，以便我可以调用该方法并更新不同项（类）的库存。我不熟悉泛型，经过研究，我写了下面的代码：

public virtual void UpdateInventory<PurchasedEntity, Inventory>(IEnumerable<PurchasedEntity> purchaseDetails, GenericRepository<Inventory> inventory, Expression<Func<Inventory, bool>> filterForInventory) 
            where PurchasedEntity : class
            where Inventory : class

{
    foreach (var item in purchaseDetails)
    {
        var glitterInventory = inventory.GetAll(filterForInventory);
        if (!glitterInventory.Any())
        {
            var newInventory = (Inventory)Activator.CreateInstance(typeof(Inventory), new object[] 
            {
                GlitterId = item.GlitterId,
                Quantity = item.Quantity,
                TotalPrice = (decimal)item.Quantity * item.UnitPrice,
                UnitPrice = item.UnitPrice,
                CreatedBy = User.Identity.Name,
                CreatedDate = DateTime.Now,
            });

            inventory.Insert(newInventory);
        }
        else
        {
            var updateInventory = glitterInventory.First();
            updateInventory.Quantity += item.Quantity;
            updateInventory.TotalAmount += (decimal)item.Quantity * item.UnitPrice;
            updateInventory.UnitPrice = (decimal)updateInventory.Quantity / updateInventory.TotalAmount;
            updateInventory.UpdatedBy = User.Identity.Name;
            updateInventory.UpdatedDate = DateTime.Now;
            inventory.Update(updateInventory);
        }
    }
}

问题是我收到以下错误：

'PurchasedEntity' does not contain a definition for 'GlitterId' and no extension method 'GlitterId' accepting a first argument of type 'PurchasedEntity' could be found (are you missing a using directive or an assembly reference?)

如何删除此错误并获取该类的属性？

我甚至不知道我写的代码是否有用，如果你能改进它，那就太好了，那就太好了。感谢。