How Can I Effectively Translate SQL CASE Statements into LINQ Queries?

Translating SQL CASE Statements to LINQ: A Practical Guide

This article addresses the challenge of converting SQL CASE statements into their LINQ equivalents. A user sought assistance in translating the following SQL snippet:

<code class="language-sql">osc_products.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>

The initial LINQ attempt provided was insufficient:

<code class="language-csharp">cdsDBDataContext db = new cdsDBDataContext();
  var query = from items in db.cdsItems
              where items.ItemHandHeldFlag.Equals("Y") && 
              items.ItemQtyOnHand -  items.ItemQtyCommitted > 0
  select items;</code>

This query only filters data; it doesn't implement the logic of the SQL CASE statement.

For a clearer illustration of LINQ's CASE statement equivalent, let's examine a simpler example:

<code class="language-csharp">Int32[] numbers = new Int32[] { 1, 2, 1, 3, 1, 5, 3, 1 };

var numberText =
(
    from n in numbers
    where n > 0
    select new
    {
        Number = n,
        Text = 
        (
            n == 1 ? "One" :
            n == 2 ? "Two" :
            n == 3 ? "Three" : "Unknown"
        )
    }
);</code>

This demonstrates the use of the ternary conditional operator (?:) to mimic the behavior of a CASE statement. The conditions are evaluated sequentially, returning the appropriate value for each match. The result is a sequence of anonymous objects, each containing a number and its textual representation. Applying this principle to the original SQL CASE statement requires a similar nested conditional approach within the LINQ query, adapting it to the specific data structure and relationships within db.cdsItems and potentially joining with other tables to access itempromoflag, itemcat1, and itemsalestatus. The ELSE condition would represent the default value if none of the preceding conditions are met.

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