if-else equivalent via linq-to-sql query in where clause c#

Question

Basically I wanted to have an if-else statement in my linq to sql statement.

var query = from d in database
            if(x == y) {
                where d.Attr = x
            }
            else {
                 where d.Attr = y
            }
            select d;

Any ideas?

I'm guessing that this is just an example, and that you aren't actually using that check, because if you are, it will always resolve the case for the value of 'y'. x=4, y=3 use the else (3) x=3, y=3 use the if (3) — Robaticus, May 21 '10 at 21:11

score 8 · Answer 1 · answered May 21 '10 at 21:06

8

Supposing, you meant == and not =:

from d in database
where (x == y && d.Attr == x) ||
      (x != y && d.Attr == y)
select d;

answered May 21 '10 at 21:06

Frank Krueger

69,552
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if x and y are not parameters of `database`, it would be better to move the if outside the LINQ query – BlueRaja - Danny Pflughoeft May 21 '10 at 22:03
Since `x==y` will have the same truth value for all elements of `database`, there is no reason to translate both `d.Attr == x` and `d.Attr == y` to SQL. – BlueRaja - Danny Pflughoeft May 22 '10 at 04:20

tvanfosson · Accepted Answer · 2010-05-21T21:26:35.247

Isn't that just the same as

var query = from d in database
            where d.Attr == y
            select d;

Your situation (or a similar, more realistic one) can be handled with a simple conditional in the where clause. For more complex queries you can use the extension methods to build up a query implementing conditionals pretty easily or use a PredicateBuilder to create arbitrarily complex conditions.

var query = db.Table;
if (x == y)
{
   query = query.Where( d.Attr == z );
}
else
{
   query = query.Where( d.Attr == t );
}

var predicate = PredicateBuilder.True<Foo>()
                                .And( f => f.Attr == y )
                                .And( f => f.Attr == x )
                                .Or( f => f.Attr == z );
var query = db.Foo.Where( predicate );

Hahah well I gave a bad example. Thanks for the answer, this helped a lot. — Darcy, May 25 '10 at 18:27

score 0 · Answer 3 · answered May 21 '10 at 21:06

0

EDIT: I think I may have misunderstood what you wanted to do.

I'm not sure if the ? (ternary) operator will work in Linq to SQL, but try this:

from d in database select (x == y) ? x : y

answered May 21 '10 at 21:06

Daniel Plaisted

16,674
4
44
56

score 0 · Answer 4 · answered May 21 '10 at 21:10

0

wouldnt

if(x == y) { 
                where d.Attr = x 
            }

be the same as

if(x == y) { 
                where d.Attr = y 
            }

if x==y?

so couldnt you just use

where d.Attr = y

answered May 21 '10 at 21:10

Greg Olmstead

1,551
10
22

score 0 · Answer 5 · answered May 21 '10 at 21:39

This is the solution, assuming you meant == and not =:

var query = from d in database
            where (x == y ? d.Attr == x : d.Attr == y)
            select d;

However, this is logically equal to the following:

var query = from d in database
            where d.Attr == y
            select d;

Because, if x == y is true, then d.Attr == x and d.Attr == y will be equal.

score 0 · Answer 6 · answered Mar 06 '15 at 11:23

0

var query = from d in database where (x == y)? d.Attr = x : d.Attr = y select d;

answered Mar 06 '15 at 11:23

naveen

1

if-else equivalent via linq-to-sql query in where clause c#

6 Answers6