Lambda expression using Join for something more than a simple key

Question

I'd like to do a Join but I need to compare more than just a simple key. For example, I'd like to do something like the following:

from a in tableA
join b in tableB on a.x between b.minX and b.maxX

Not very complicated. But the functions for the Join lambda method seem to want a simple key to compare.

Any thoughts?

@Tim I don't think there is a appropriate where clause, because I'm trying to Join two tables -- so the values that go into the where clause would change according to the row in the first table. — Fernando
– Fernando, Commented Jan 5, 2012 at 19:51
(I think my formatting preserved the initial idea). Do you want to do something like a left outer join to tableB? — Roman
– Roman, Commented Jan 5, 2012 at 19:55

undefined · Accepted Answer · 2012-01-05 19:54:55Z

2

from a in tableA
from b in tableB
where a >= b.minX && a <= b.maxX
select a;

answered Jan 5, 2012 at 19:54

undefined

34.4k23 gold badges136 silver badges203 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Fernando Over a year ago

Is this even legal? And what is the lambda expression equivalent?

Roman Over a year ago

@Fernando: Of course it's legal, it's a Cartesian join and a filter on the result. And what do you mean by "lambda expression equivalent?"

Fernando Over a year ago

example: myThings.Where(thing => thing <= 25)

Roman Over a year ago

@Fernando: A double from clause translates to a SelectMany, if that's what you're asking.

Gab · Accepted Answer · 2012-01-05 20:01:00Z

0

Something like this?

var fdts = from fdt in context.FeuilleDeTemps.Include("FeuilleDeTempsJournees")
           where
               (employes.Contains(fdt.ID_Employe)) &&
               (fdt.DateDepart <= date) &&
               (fdt.DateFin >= date)
           orderby fdt.ID_Employe
           select fdt;

or in your case

var v = from a in context.tableA.Include("tableB")
        where
            a.x < b.minX &&
            a.x > b.maxX
        select v;

edited Jan 5, 2012 at 20:01

answered Jan 5, 2012 at 19:53

Gab

5,8548 gold badges40 silver badges53 bronze badges

Comments

Tormod · Accepted Answer · 2012-01-05 20:30:07Z

0

You asked specifically for the dotted syntax?

        var tableA = new[] {1, 2, 3, 4};
        var tableB = new[]
                         {
                             new {minX = 1, maxX = 2},
                             new {minX = 3, maxX = 6},
                             new {minX = 5, maxX = 7},
                             new {minX = 6, maxX = 8},
                         };
        var res = tableA.SelectMany(a => tableB, (a, b) => new {a, b}).Where(t => t.a >= t.b.minX && t.a <= t.b.maxX)
                .Select(t => t.a);

answered Jan 5, 2012 at 20:30

Tormod

4,5832 gold badges33 silver badges52 bronze badges

2 Comments

Fernando Over a year ago

Thanks for the additional help!

Tormod Over a year ago

You're welcome. You can, of course, optimize by putting in the check predicate within the first argument passed to SelectMany, ie "a=>tableB.Where(b=>((a<b.maxX)&&(a>b.minX))) " so you don't have to new() the tuple before checking.

Collectives™ on Stack Overflow

Lambda expression using Join for something more than a simple key

3 Answers 3

4 Comments

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related