데이터 업데이트를 위한 LINQ 쿼리에서 SQL CASE 문을 어떻게 복제할 수 있습니까?

<code class="language-sql">UPDATE osc_products
SET products_quantity =
    CASE 
        WHEN itempromoflag = 'N' THEN 100000
        WHEN itemcat1 IN ('1','2','31') AND itemsalestatus = 'S' THEN 100000
        WHEN itemsalestatus = 'O' THEN 0
        ELSE cds_oeinvitem.itemqtyonhand - cds_oeinvitem.itemqtycommitted 
    END</code>

<code class="language-csharp">cdsDBDataContext db = new cdsDBDataContext();
var query = from items in db.cdsItems
            where items.ItemHandHeldFlag == "Y"
            let quantity =
                (
                    items.ItemPromoFlag != 'N' ? 100000 :
                    (items.ItemCat1.In("1", "2", "31") && items.ItemSaleStatus == "S") ? 100000 :
                    items.ItemSaleStatus == "O" ? 0 :
                    items.ItemQtyOnHand - items.ItemQtyCommitted
                )
            select new
            {
                ItemId = items.ItemId,
                UpdatedQuantity = quantity
            };</code>