Question

I have this functional Linq-to-Sql statement.

public IEnumerable<int> GetChildIds(IEnumerable<int> selectedParentIds)
{
    using (var context = new MyContext())
    {
        return context.Children
            .Where(c => selectedParentIds.Contains(c.parentId))
            .Select(c => c.Id)
            .ToList();
    }
}

It gives me the selected child Id’s, as requested but, I’ve been running SQL Profiler.

This statement appears to send a seperate request to the database for each selectedParentId which seems sub-optimal to me.

Is there a way I can restructure this statement to minimise the traffic with the server? Is there a different approach I should take or, is this just as good as it gets?

EDIT

Thanks for the guidance.

This is a mistake on my interpretation of my trace ouput, Linq-To-SQL make a perfectly reasonable statement for SQLServer 2005 just as it does for SQLServer 2008. The problem is elsewhere.

Answer 1

The same query using LINQ to SQL against SQL 2008 produces a single SQL query. Are you able to test against SQL Server 2008?

For example:

IEnumerable<int> list = new List<int>{1,2,3};

Models.Where (m => list.Contains(m.Id)).Select (m => m.Id).ToList();

Produces

-- Region Parameters
DECLARE @p0 Int = 1
DECLARE @p1 Int = 2
DECLARE @p2 Int = 3
-- EndRegion
SELECT [t0].[Id]
FROM [Models] AS [t0]
WHERE [t0].[Id] IN (@p0, @p1, @p2)

And the same thing using Entity Framework produces

SELECT 
[Extent1].[Id] AS [Id]
FROM [dbo].[Models] AS [Extent1]
WHERE [Extent1].[Id] IN (1,2,3)

So without being able to check this against SQL 2005, I’m going to risk it and say, no there’s nothing you can do unless you upgrade the server.