Optional requirement on where clause in LINQ

Question

The goal is to build a search form that can be entered on multiple field searches. But entering all fields are optional. What is the equivalent code in LINQ? Thanks.

string str = "";
if(a!="")
    str += "f1 == a";
if(b!="")
    str += " && f2 == b";
if(c!="")
    str += " && f3 == c";

select f1, f2, f3 from p
where str;

score 4 · Answer 1 · answered Jun 03 '13 at 02:05

4

You can build up the query sequentially in the same way, something like this:

var query = someData.Items;

if  (a != string.Empty)
    query = query.Where(x => x.f1 == a);

if (b != string.Empty)
    query = query.Where(x => x.f2 == b);

…and so on. In the end, you have built a query with only the relevant predicates.

answered Jun 03 '13 at 02:05

Jay

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+1 for actually using LINQ features, and giving an answer that will perform much better than the alternative of having the SQL server/LINQ driver try to optimize out the irrelevant portions (which it usually? does, but not always) – Robert McKee Jun 03 '13 at 07:41

score 1 · Accepted Answer · answered Jun 03 '13 at 02:02

Try

from x in p where (x.f1 == a || a == "") && (x.f2 == b || b == "") && (x.f3 == c || c == "") select new { f1 = x.f1, f2 = x.f2, f3 = x.f3 }

The or on each search variable makes it ignored when empty string. I'm assuming you already took care of nulls in a, b, c.

Optional requirement on where clause in LINQ

2 Answers2