If condition in LINQ Where clause

Question

With Linq, can I use a conditional statement inside of a Where extension method?

Solution 1

var query = someList.Where(a => (someCondition)? a == "something" : true);

so, if 'someCondition' is false, 'Where' will be skipped.

Solution 2

Yes you can like:

var query = someList.Where(a => a == "something");
if (condition)
{
    query = query.Where(b => b == "something else");
}
var result = query.ToList();

Because Where is producing an IQueryable, the execution is deferred until the ToList in my example so you can chain Wheres together as much as you want and then just execute it after you have passed all your conditions.

Solution 3

Make use of WhereIf extenstion method avaialbe in linq

Example

if (SearchControlMain.PostingID.HasValue) 
    query = query.Where(q => q.PostingID == SearchControlMain.PostingID);

instead of above go for the below

query = query.WhereIf(SearchControlMain.CategoryID.HasValue, q => q.CategoryID == SearchControlMain.CategoryID);

LINQ WhereIf Extension Method

LINQ to SQL Where Clause Optional Criteria

Solution 4

Not sure if this is appropriate but it is quite useful, you can use ifs quite handily with conditional where clauses:

 var r = (from p in productinfo.tblproduct
                     where p.Accountid == accountid
                     select p);

            if (uuf1 != null)
                r = r.Where(p => p.UnitUserField1 == uuf1);

            if (uuf2!= null)
                r = r.Where(p => p.UnitUserField2 == uuf2);

So the where clause will be amended according to what is in UUF1 or UUF2 i.e. you might have only UUF1 with info, in which case it will take that and ignore the UUF2 where clause, you might have both in which it will take both or you might not have anything in UUF1 or 2 and your where clause will just take the accountid as the where clause.

Solution 5

In my case there were two "conditional" where depending on search keys, so I did:

    var query = db.Package.Include("SomeThing")
    .Where(item => searchString1 == null || searchString1 == "" || item.Contains(searchString1))
    .Where(item => searchString2 == null || searchString2 == "" || item.Contains(searchString2));
    ...

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Comments

[Mel Gerats]

Which is equal to: list.Where(item => Foo(item));

[Omer]

Where is not producing IQueryable, it is producing IEnumerable. Wrong answer

[D Hansen]

@OmerK Where does in-fact product IQueryable, if the object you are running the extension method on is also an IQueryable, if you run it on an IEnumerable, you will get an IEnumerable.

[logical8]

Analog (little shorter): var query = someList.Where(a => !someCondition || a == "something");

[itmuckel]

This is only viable if you don't need the element's value in the condition.