how to check null value in linq to sql

Question

I am trying to use following linq to sql query to get result. But it doesn't works if parentCategoryId passed as null

 public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId)
    {
        var categories = from c in source where c.ParenCategoryId == parentCategoryId select c;
        return categories;
    }

but following works if null used directly in place of parentCategoryId

 public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId)
    {
        var categories = from c in source where c.ParenCategoryId == null select c;
        return categories;
    }

check if(ParenCategoryID isEqualTo:NULL) then do what you want. — vishiphone
– vishiphone, Commented May 5, 2012 at 9:32

Magnus · Accepted Answer · 2012-05-05 09:38:39Z

8

You can use object.Equals, it will match on null values also.

public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId)
{
    var categories = from c in source 
                     where object.Equals(c.ParenCategoryId, parentCategoryId) 
                     select c;
    return categories;
}

edited May 5, 2012 at 9:38

answered May 5, 2012 at 9:33

Magnus

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3 Comments

Renatas M. Over a year ago

object.Equals will be translated to sql? if yes how query will look like?

Magnus Over a year ago

@Reniuz Yes it will, it will be: WHERE [t0].[ParenCategoryId] IS NULL

Michael Buen Over a year ago

@Reniuz yes, and it is optimized by Linq to Sql depending on the nullable variable's value: brentlamborn.com/post/…

sarwar026 · Accepted Answer · 2012-05-05 09:49:01Z

0

You can try the following

public static IEnumerable<Category> GetChildren(this Table<Category> source, int? parentCategoryId)
{
    var categories = from c in source 
                     where (parentCategoryId != null? c.ParenCategoryId == parentCategoryId : c.ParenCategoryId == null)
                     select c;
    return categories;
}

answered May 5, 2012 at 9:49

sarwar026

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