Getting only specific columns in entity framework lambda join

Question

I am surprised I cannot find a solution for this on the web, but wording the search terms was a bit difficult. The question I have is about generating entity SQL that only returns the needed columns in a group join using Lambda syntax.

The following is a "toy" example. I am not joining on two entities, rather on an enumerated list and an entity. And tunnelling is not an acceptable answer. I need to apply this to a much larger problem using a group join and select many.

var result1 = clientprofiles.Join(Context.Adjusters,
c => c.AdjusterId,
a => a.AdjusterId,
(c, a) => new {a.ClientAccountId}).ToList();

Using Julie Lehrman's Entity profiler, I see that the query is being generated to select every record in the rows that meet the join criteria. How do I pare it down so it only selects the ClientAccountId field in this example?

Looking at stackoverflow.com/questions/1531934/… could you try Context.Adjusters.Select(a=> new { a.ClientAccountId}) as your first argument to the join? — Steve Mitcham
– Steve Mitcham, Commented Feb 12, 2015 at 20:44
SELECT [Extent1].[AdjusterId] AS [AdjusterId] FROM [dbo].[Adjuster] AS [Extent1] ... worked perfectly. — Frank M
– Frank M, Commented Feb 12, 2015 at 20:54
Yeah, but great intuition. I kept trying to make a select below the join — Frank M
– Frank M, Commented Feb 12, 2015 at 21:00

Steve Mitcham · Accepted Answer · 2015-02-12 20:56:55Z

1

You can project a set of columns on any select from the context, so in your case you can constrain the Context.Adjusters parameter by using

Context.Adjusters.Select(a=> new { a.ClientAccountId })

to constrain the query to just the single column

answered Feb 12, 2015 at 20:56

Steve Mitcham

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