How to Convert SQL CASE Statements to LINQ Queries?

CASE statement in LINQ: understanding and implementation

The CASE statement in LINQ allows developers to evaluate multiple conditions and assign specific values ​​based on the results. They are commonly used for data transformation and manipulation.

Convert complex CASE statements to LINQ

Let us consider the CASE statement provided in the original question:

<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>

This statement assigns specific values ​​to the products_quantity field of the osc_products table based on various conditions. To convert it to LINQ we can use the following syntax:

<code class="language-csharp">var productsQuantity = 
    osc_products
    .Select(x => new
    {
        x.products_quantity,
        ItemPromoFlag = x.itempromoflag != "N",
        ItemCategory1 = new[] { "1", "2", "31" }.Contains(x.itemcat1),
        ItemSaleStatus = x.itemsalestatus == "S",
        AvailableQuantity = x.itemqtyonhand - x.itemqtycommitted
    })
    .Select(x => x.products_quantity = 
        x.ItemPromoFlag ? 100000 :
        (x.ItemCategory1 && x.ItemSaleStatus) ? 100000 :
        x.itemsalestatus == "O" ? 0 :
        x.AvailableQuantity
    );</code>

Understanding LINQ conversion

This LINQ statement projects a new anonymous type that contains the existing products_quantity field and additional properties that hold the boolean value of the conditional expression. It then uses a nested Select operation to conditionally assign the calculated products_quantity value.

Simple CASE statement example

The provided code example for converting a simple CASE statement to LINQ demonstrates the use of ternary expressions in a Select clause:

<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 statement uses a ternary expression to assign a different text value to a number based on its value. The syntax of ternary expression is:

<code class="language-csharp">condition ? true_expression : false_expression</code>

These examples illustrate how to convert CASE statements into LINQ, providing a concise and easy-to-maintain way to evaluate conditions and assign values ​​to your data.

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