Entity Framework 5.0. What is wrong with my Query?

Question

This is my code: ``` public DateTime GibSomeStartDate(IEnumerable<int> partnerNumbers, DateTime startTime) { var contractsStartDate = from contract in this.databaseContext.Contract where partnerNumbers.Contains(contract.Pnr) && contract.SomeDateTime >= startTime select contract.SomeDateTime; } ``` if I call `contractsStartDate.Min()` an Exception occurs: ``` Unable to create a null constant value of type 'System.Collections.Generic.IEnumerable`1'. Only entity types, enumeration types or primitive types are supported in this context. ``` What is wrong with my Query? the `contractsStartDate` is of type `System.Data.Entity.Infrastructure.DbQuery` EF 5.0 `databaseContext` is child of `System.Data.Entity.DbContext`

Accepted Answer

I know this error. Just Make sure `partnerNumbers` is not null. You're passing a null value for this parameter, but Linq-to-entities can't translate that value to anything meaningful.

```
if (partnerNumbers == null)
{
    throw new ArgumentNullException("partnerNumbers");
}
```

An additional bonus advice:

If `SomeDateTime` is `not nullable` and there are no entries in your enumeration, then you'll get an exception on calling `Min()`. Casting `SomeDateTime` to the `nullable` type in your query will work, then you get null when there are no entries.

Entity Framework 5.0. What is wrong with my Query?

Solution

Problem