If-else is equivalent to querying linq-to-sql in where, where C #

Question

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

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

Any ideas?

Answer 1

Isn't it like that

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 where clause. For more complex queries, you can use extension methods to simplify the creation of query execution conditions or use 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 );

Answer 2

Suppose you had in mind ==, and not =:

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

Answer 3

EDIT: , , , , .

, ? () Linq SQL, :

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

Answer 4

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

,

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

x == y?

where d.Attr = y

Answer 5

This is a solution, assuming you meant ==, 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 == ytrue, then d.Attr == xthey d.Attr == y will be equal.

Answer 6

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