public IRepository<OrderItem> orderItems { get; set; }

    private List<OrderHeld> _releasedOrders = null;
    private List<OrderHeld> releasedOrders
    {
        get
        {
            if (_releasedOrders == null)
            {
                _releasedOrders = new List<nOrderHeld>();
            }
            return _releasedOrders;
        }
    }

    .....

    public int GetReleasedCount(OrderItem orderItem)
    {
        int? total =
            (
                from item in orderItems.All
                join releasedOrder in releasedOrders
                    on item.OrderID equals releasedOrder.OrderID
                where item.ProductID == orderItem.ProductID
                select new
                {
                    item.Quantity,}

            ).Sum(x => (int?)x.Quantity);

        return total.HasValue ? total.Value : 0;
    }

当我对数据库运行它时,我收到一个我不太懂的错误.

Exception information:
Exception type: System.NotSupportedException
Exception message: Local sequence cannot be used in LINQ to sql
implementation of query operators
except the Contains() operator.

我究竟做错了什么？

我猜这与orderItems在数据库上并且releasedItems在内存中的事实有关.

编辑

我根据给出的答案更改了我的代码(谢谢大家)

public int GetReleasedCount(OrderItem orderItem)
    {
        var releasedOrderIDs = releasedOrders.Select(x => x.OrderID);

        int? total =
            (
                from item in orderItems.All
                where releasedOrderIDs.Contains(item.OrderID)
                   && item.ProductID == orderItem.ProductID
                select new
                {
                    item.Quantity,}

            ).Sum(x => (int?)x.Quantity);

        return total.HasValue ? total.Value : 0;
    }