LINQ to SQL Null check in Where Clause

• Posted by Brent on June 25, 2008 14:34
• Comments (2)

After testing several LINQ queries for ways to do a null comparison in the where clause, I found only one way to do it that returns the result set as though I had used "IS NULL" in a standard SQL query. The key is to use the object.Equals() method:

   1:private ProductDataContext db = new  ProductDataContext();

   2:   

   3:/// <summary>

   4:/// Return all products for a given manufacturer

   5:/// </summary>

   6:/// <param name="manufacturerName"></param>

   7:/// <returns></returns>

   8:public IQueryable<Product> GetProdByManu(String manufacturerName, int? catId)

   9:{

  10:   

  11:    var products = from o in db.Products

  12:                   where o.manufacturerName == manufacturerName

  13:                   && object.Equals(o.categoryID, catId)

  14:                   select o;

  15:             

  16:   

  17:    if(products.Count() > 0)

  18:    {

  19:        return products;

  20:    }

  21:    else

  22:    {

  23:        return null;

  24:    }

  25:}

The above method GetProductsByManu accepts a parameter catID , a nullable integer. When calling the method if I pass null as the value for catID , LINQ will correctly return products where categoryID is null in the database.  I find that if I use == null as show below, the results are inaccurate:

   1:    var products = from o in db.Products

   2:                             where o.manufacturerName == manufacturerName

   3:                             && o.categoryID == null

   4:                             select o;

In the above case, even though my tables contain products with a null categoryID, those products are not returned by LINQ. I'm not sure exactly why this is, and maybe someone with more LINQ experience than I can shed some light in the comments. I just know from now on, when doing a check for null in a LINQ where clause, object.Equals() is what I'll be using.

Hope this helps someone else with the same issues I had! :)

Visual Studio 2008 - Clear Recent Projects List

• Posted by Brent on May 27, 2008 03:15
• Comments (0)

Have you ever wanted to clear your "Recent Projects" list on your Visual Studio 2008 start page? If so here's a .reg file that will do it for you:

 Windows Registry Editor Version 5.00

[-HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\ProjectMRUList]
[HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\ProjectMRUList]

Just copy the above contents into a new file named anything you like, with a .reg extension. When your Recent Projects list gets cluttered and you want to clear it, just double-click the .reg file you just created and it will clear your list.

Flex Scrollbar - Remove up - down arrows

• Posted by Brent on May 20, 2008 13:28
• Comments (3)

Add the following CSS to your Flex application to remove up/down arrows from all scrollbars:

 HScrollBar{
up-arrow-skin: ClassReference( null );
down-arrow-skin: ClassReference( null );
}
VScrollBar{
up-arrow-skin: ClassReference( null );
down-arrow-skin: ClassReference( null );
}

Enum as the data source for drop-down list - ASP.NET

• Posted by Brent on November 28, 2007 11:32
• Comments (0)

I've been using enum's a lot lately. Here is another enum snippet for my snippet collection showing how to use an enum as the source for the items in a drop down.