Efcore: Queries swallowing exceptions that should be thrown

[vflame]

It appears that under certain conditions, EF Core is swallowing LINQ expressions exceptions that should throw. This is unexpected behavior.

Steps to reproduce

``` C#
context.Add(new ConcreteB("01"));
context.Add(new ConcreteB("02"));
context.Add(new ConcreteB("03"));
context.Add(new ConcreteB("04"));
context.Add(new ConcreteB("05"));
context.SaveChanges();

        var count = context.Set<ConcreteB>().Count(p => p.Id.Contains("0")); //count is 5
        var q = from concreteA in context.Set<ConcreteA>()
                select new
                {
                    a = concreteA.Id,
                    b = context.Set<ConcreteB>().Single(p => p.Id.Contains("0")), //Does not throw as expected. This should throw...
                    //c = context.Set<ConcreteB>().Single(), //Throws as expected
                };

        //var query = q.ToQueryString();
        var list = q.ToList();

```
-->

Further technical details

EF Core version: 5.0.0-preview.8.20325.10
Database provider: Microsoft.EntityFrameworkCore.SqlServer 5.0.0-preview.8.20325.3
Target framework: 5.0.0-preview
Operating system: Win10
IDE: Visual Studio 2019 16.3

[smitpatel]

Refer to https://github.com/dotnet/efcore/issues/15559

Throwing exception for First/Single/Last (or Default variations) requires to evaluate it on client since database does not throw exception. For a subquery, that behavior is not helpful. Further, in EF6 also Single in a subquery behaved like First only.

Exception throwing can be different for many other scenarios like arithmetic overflow, if database does not have same throwing behavior as C# then you will see difference.

[vflame]

Isn't the behavior inconsistent when:
context.Set<ConcreteB>().Single(p => p.Id.Contains("0")) doesn't throw but context.Set<ConcreteB>().Single() does throw?

[smitpatel]

Please provide a self-containing runnable repro code.

[smitpatel]

Actually, context.Set<ConcreteB>().Single() because it is not correlated with query in any form, so it is evaluated on client and converted to a parameter for query even before we start translating the query. Single with predicate has lambda so we did not evaluate it on client before translating the query.