140

When a method returns IEnumerable<T> and I do not have anything to return, we can use Enumerable.Empty<T>().

Is there an equivalent to the above for a method returning IQueryable<T>

Numan
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6 Answers6

221

Maybe: 

Enumerable.Empty<T>().AsQueryable();
Sunny
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    I know, currently that is the only simple, direct & dirty ;-) solution – Numan Apr 23 '10 at 11:04
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    Unfortunately that doesn't create an actual empty IQueryable, which means it causes e.g. `Union` queries to be broken up into multiple queries instead of one. – NetMage May 22 '17 at 23:11
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    @NetMage That's right. What is more confusing is that your code don't break in the line where is `Union`, but probably when you try something after this. This answer is accepted and voted but it can be very misleading. @Sunny Please consider to edit your answer. Answer in this question helped me: [Enumerable.Empty().AsQueryable(); This method supports the LINQ to Entities infrastructure and is not intended to be used directly from your code](https://stackoverflow.com/questions/37815309/enumerable-emptyt-asqueryable-this-method-supports-the-linq-to-entities-i) . – Lazar Đorđević May 19 '21 at 20:09
35

Enumerable.Empty<T>().AsQueryable(); should do it.

Paul Fleming
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Josh
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7

Try return new T[0].AsQueryable();

bdukes
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alejandrobog
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7

Say you have an IQueryable<T> called result:

return result.Take(0);
Protector one
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5

I would advise against alejandrobog's answer as this will still use memory to create an empty array. 

Array.Empty<T>().AsQueryable();

or

Enumerable.Empty<T>().AsQueryable();

are preferred. Array.Empty will allocate a static typed array so only one empty array of T is created and that is shared amongst all Empty queryables.

Josh
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  • `Array.Empty` is only available after .NET Framework 4.6. For earlier versions, you can use `new object[0].Cast()` – TZU Dec 20 '19 at 21:13
1

Enumerable.Empty().AsQueryable(); is wrong since Union will break and wont work. Workaround is

var db = new DbContext();
var query = db.Set<T>().Take(0);
valentasm
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  • Take(0) is the right approach. The Empty() way also breaks Concat, and probably any other method that tries to build on the empty queryable. – Mark Smith Dec 12 '22 at 22:30