Question

I’m trying to convert the following SQL into Linq but getting confused when I try to apply the min. Basically I have a table which contains Beams and their allowed loads. I then query the database and Find the smallest beam by type, which has the required strength. The following t-SQL

select
    sed.SEDetailID
from
    dbo.StructuralElementDetail sed
    inner join (select StructuralElementID, min(Ix) as MinIX from dbo.StructuralElementDetail where Ix >= @iRequired group by StructuralElementID) o
        on sed.StructuralElementID = o.StructuralElementID
            and sed.Ix = o.MinIX
order by
    StructuralElementID,
    Sequence;

returns the smallest beam by type where they have the required strength.

I already have the beams loaded into a Dictionary keyed by their IDs, so thought I should be able to query that object rather than make another call to the database.

My dictionary is

Dictionary<int, Beam>;

I’m trying something like this but getting confused how I get just the smallest beam by each Type.

            var Beams = db.Values.Where(specificBeam => specificBeam.Ix >= iRequired)
                .GroupBy(specificBeam => specificBeam.ElementType)
                    .Select(sb => new { sb.Key, MinIActual = sb.Min(specificBeam => specificBeam.Ix) });

Any pointers? Can I nest a First combined with

Answer 1

This has now been tested in a LINQPad example here.

var smallestBeamForTypes = 
    from anyBeam in db.Values
    where anyBeam.Ix >= iRequired
    group anyBeam by anyBeam.ElementType into beamTypeGroup
    let minIx = beamTypeGroup.Min(beam => beam.Ix)
    select new {
        ElementType = beamTypeGroup.Key,
        SmallestBeam = beamTypeGroup.First(beam => beam.Ix == minIx)
    };

You can then loop over like so:

foreach(var smallestBeamForType in smallestBeamForTypes)
{
    Console.WriteLine("For the element type {0} the smallest beam is {1}",
        smallestBeamForType.ElementType, smallestBeamForType.SmallestBeam);
}