If condition in LINQ Where clause

Question

Can I use if clause with Linq where?

Answer 1

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

Answer 2

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));
    ...

Answer 3

from item in items
where condition1
&& (condition2 ? true : condition3)
select item

This is how can you can do it with the noob Linq syntax. This applies the condition3 only if condition2 is false. If condition2 is true, you are essentially doing && true which has no effect on the where clause.

So it is essentially doing this:

if(condition2)
{
    from item in items
    where condition1
    select item
else
{
    from item in items
    where condition1
    && condition3
    select item
}

Answer 4

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

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

Answer 5

I had a scenario like this where I had to check for null within the list itself. This is what I did.

items = from p in items
        where p.property1 != null   //Add other if conditions
        select p;

// Use items the way you would use inside the if condition

But as Kelsey pointed out this would work too -

items = items.Where(a => a.property1 != null);

Answer 6

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.