My name
is
Jon Skeet

LINQ statement needs to be optimized

I have the following code

var x = from e in db.Employees
    where e.id == 746
    join f in db.CoWorker on e.CoWorkerID equals f.ID into fa
    from fr in fa.DefaultIfEmpty()
    select new
    {
      e.id,
      e.name,
      coWorkerName = fr.FirstName + " " + fr.LastName
    };

When i run that code in LINQpad the SQL query looks like

SELECT
  [Extent1].[id] AS [id],
  [Extent1].[name] AS [name],
  CASE WHEN ([Extent2].[ID] IS NULL) THEN CASE WHEN ([Extent2].[FirstName] IS NULL) THEN N'' ELSE [Extent2].[LastName] END + N' ' + CASE WHEN ([Extent2].[LastName] IS NULL) THEN N'' ELSE [Extent2].[LastName] END END AS [C1]
FROM  [dbo].[Employees] AS [Extent1]
LEFT OUTER JOIN [dbo].[CoWorker] AS [Extent2] ON [Extent1].[CoWorker] = [Extent2].[ID]
WHERE 1615 = [Extent1].[id]

How do i get rid of the CASE WHEN block?

Here's a query which performs the concatenation client-side instead. As you can see, it's more long-winded - you should absolutely check that it makes a significant difference before you decide to embrace it:

var dbQuery = from e in db.Employees
              where e.id == 746
              join f in db.CoWorker on e.CoWorkerID equals f.ID into fa
              from fr in fa.DefaultIfEmpty()
              select new { e.id, e.name, fr.FirstName, fr.LastName };
var query = dbQuery.AsEnumerable()
                   .Select(x => new {
                       x.id,
                       x.name,
                       coWorkerName = x == null 
                           ? ""
                           : x.FirstName + " " + x.LastName
                   });

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