How Can I Replicate SQL CASE Statements in LINQ Queries for Data Updates?

LINQ's Approach to Conditional Data Updates

LINQ (Language Integrated Query) provides efficient ways to manage conditional logic, mirroring the functionality of SQL's CASE statements, particularly when updating database records. Let's examine how to achieve this.

A common scenario involves updating a column based on multiple conditions. Consider this SQL example:

<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>

This SQL statement updates products_quantity based on different criteria. The equivalent LINQ query would be:

<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>

This LINQ query uses the let keyword to define a calculated quantity based on the conditional logic. The ternary operator (? :) provides a concise way to implement the CASE statement's functionality. The final selection includes the ItemId and the calculated UpdatedQuantity, enabling efficient database updates.

This showcases the flexibility of LINQ in handling complex conditional updates, providing a powerful alternative to direct SQL CASE statements within your C# code.

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