Resolving bool from linq query

Question

I have a property OnHomePage which is a bool.

I am trying to set this value based on whether a result is returned from a linq query or not. Obviously I could write an external method to determine whether the result of my query is null or whether it holds a value but I am hoping there is a better way for it to be done in one line.

Here is my current line of code as it stands:

OnHomePage = im.PageImages.Select(p => p.ImageId == im.Id 
                                      && p.Page.PageName == "/Home")

everybody answered without thinking , DOES your bool should return true if at least 1 is true , or ALL of them ....? — Royi Namir, May 01 '12 at 13:57
@RoyiNamir: I don't think that's fair to say. Speaking just for myself, I did pay attention to *"whether a result is returned from a linq query or not."* That's `Any`. — Jon, May 01 '12 at 13:58

score 4 · Accepted Answer · answered May 01 '12 at 13:55

4

You can use the Any Extension Method to determine if a query gives any result or not:

OnHomePage = im.PageImages.Any(p => p.ImageId == im.Id 
                                   && p.Page.PageName == "/Home");

answered May 01 '12 at 13:55

dtb

198,715
31
379
417

"Any" is especially good for this since it's short circuited and will stop iterating through the items when it finds a match. – bryanbcook May 01 '12 at 13:57
2

@bryanbcook: So does `.Where(..).Any()`. `.Any(..)` may result in a more efficient translation to SQL though, depending on the LINQ provider. – dtb May 01 '12 at 13:58
2

@bryanbcook This is likely an IQueryable, not an Enumerable, so that depends entirely on the query provider. – Servy May 01 '12 at 13:59

score 3 · Answer 2 · answered May 01 '12 at 13:55

3

You should simply wrap up the query with .Any:

OnHomePage = im.PageImages.Where(p => p.ImageId == im.Id 
                                  && p.Page.PageName == "/Home")
                          .Any();

Or, just use the other overload of Any directly in the first place:

OnHomePage = im.PageImages.Any(p => p.ImageId == im.Id 
                                  && p.Page.PageName == "/Home");

answered May 01 '12 at 13:55

Jon

396,160
71
697
768

2

need to change the `Select` to a `Where` in the first query. The second query is fine. – Servy May 01 '12 at 13:57

score 2 · Answer 3 · answered May 01 '12 at 13:55

2

OnHomePage = im.PageImages.Where(p => p.ImageId == 
  im.Id && p.Page.PageName == "/Home").Any();

answered May 01 '12 at 13:55

Servy

193,745
23
295
406

score 0 · Answer 4 · edited May 23 '17 at 12:04

As said other users you can use Any():

OnHomePage = im.PageImages.Any(p => p.ImageId == im.Id 
                                      && p.Page.PageName == "/Home");

Or another solution could be use Exists():

OnHomePage = im.PageImages.ToList().Exists(p => p.ImageId == im.Id 
                                          && p.Page.PageName == "/Home");

Here is an interesting answer explain the differences.

PS:

In behaviour, these are identical.

Resolving bool from linq query

4 Answers4