Tuesday, 10 July 2007

Recently we received a question from a customer about how to express a sort criteria based on a condition. As the sort expression in Genome is nothing else than an implicit function (lambda) executed on the candidate element to return the value to sort by, this can be quite easily achieved.

As a simple example, let’s use the Northwind database again. A customer there has a Country and a Region property. Imagine you want to order all customers in the USA by Region and all the other customers by Country. Additionally you want to have USA customers first, then the others.

A Genome set can be sorted using the OrderBy() method. It takes an implicit function as a parameter, which is denoted using [] in OQL. The condition can be expressed using the ? operator, which is translated to a CASE WHEN in SQL. Hence, the order function can be expressed like this:

When the customer is located in the USA, then order by region; otherwise, order by country:

Country=="USA" ? Region : Country

To make sure customers located in the USA are listed first, I am prefixing the Region with a space (I know this is a hack, but it will do for this example). Hence, the final OQL looks like this:

extentof(Customer).OrderBy( [ Country == "USA" ? " " + Region : Country])

which translates to the following SQL:

SELECT … FROM Customers
    CASE WHEN (Country="USA")
       THEN (" " + Region)
       ELSE (Country)

Posted by Chris

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Genome | OQL
Tuesday, 10 July 2007 21:00:41 (W. Europe Daylight Time, UTC+02:00)  #    Disclaimer  |  Comments [0]  | 
 Wednesday, 04 July 2007
The Genome OQL Query Analyzer (QA) is a very helpful tool when you are developing with Genome: it allows you to load a mapped business layer to execute any kind of OQL queries. In this article, I demonstrate how the latest mapped business layer, along with its mapping, can be loaded by starting the Genome QA with a single click in Visual Studio’s solution explorer.
Genome | OQL
Wednesday, 04 July 2007 13:47:14 (W. Europe Daylight Time, UTC+02:00)  #    Disclaimer  |  Comments [0]  |