Linq - Retrieve a single value in a String

Question

I use Asp.net 3.5 and EF 4.

I need find a specific row in my DataBase and display on a label a single value as string.

At the moment I use this code, it is working, so I find a single Object and read its properties.

 var myAuthor = (from at in context.CmsAuthors
             where at.AuthorId == myRow.AuthorId
             select at).Single();   
 myAuthorNameLabel.Text = myAuthor.LastName;

I would like to know:

If there is another syntax in Linq to achieve the same result.
How to do it using Lamba?
Which approach would you suggest me?

Bala R · Accepted Answer · 2011-06-07 14:13:54Z

4

Here's the method syntax (using lambdas)

myAuthorNameLabel.Text = context.CmsAuthors
                           .Where(at => at.AuthorId == myRow.AuthorId)
                           .Select(at => at.LastName) 
                           .SingleOrDefault() ?? string.Empty;

answered Jun 7, 2011 at 14:13

Bala R

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Comments

Variant · Accepted Answer · 2011-06-07 14:41:13Z

3

You can use:

 var myAuthorName = 
(from at in context.CmsAuthors where at.AuthorId == myRow.AuthorId select at).Single().Select(a => a.LastName);

actually this would be even better:

var myAuthorName = 
(from at in context.CmsAuthors where at.AuthorId == myRow.AuthorId select at).Select(a => a.LastName).Single();

Update

An example of how to use with Anonymous type:

var myAuthorNames = 
    (from at in context.CmsAuthors where at.AuthorId == myRow.AuthorId select at).Select( a => new {a.LastName, a.FirstName}).Single();

edited Jun 7, 2011 at 14:41

answered Jun 7, 2011 at 14:03

Variant

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6 Comments

GibboK Over a year ago

Thanks, could you tell me why your second option would be even better?

Variant Over a year ago

Sure, the usage of Single executes the actual database query, so in the first case the query retrieves the entire Author object and then selects the last name out of it. The second method performs a minimal db query to retrieve only the last name column.

GibboK Over a year ago

Ok I understand, what about using Anonymous Type? Could make even minimal db query? thanks for your help on this

Variant Over a year ago

In this case I don't think it can get any minimal that that. If you needed to retrieve two values then selecting an anonymous type would get you the minimal query.

GibboK Over a year ago

Thanks Variant, may I ask you if you can write down here an example with Anonymous Type? Unfortunately I'm trying but with no success. Thanks once again!

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