Implicit convert List to List

Question

I am using Linq to Entities.

Have an entity "Order" which has a nullable column "SplOrderID".

I query my Orders list as

List<int> lst = Orders.where(u=> u.SplOrderID != null).Select(u => u.SplOrderID);

I understand it is because SplOrderID is a nullable column and thus select method returns nullable int.

I am just expecting LINQ to be little smart.

How should i handle this?

Answer 1

As you are selecting the property, just get the value of the nullable:

List<int> lst =
  Orders.Where(u => u.SplOrderID != null)
  .Select(u => u.SplOrderID.Value)
  .ToList();

Answer 2

linq

var lst = (from t in Orders
           where t.SplOrderID.HasValue
           select new Order
           {
             SplOrderID = t.SplOrderID
           }).Select(c => c.SplOrderID.Value).ToList();

or

   var lst = (from t in Orders
               where t.SplOrderID.HasValue
               select t.SplOrderID.Value).ToList();

Answer 3

I found your question trying resolve the same problem, and after a few tries, i got this solution, cast int for each property on the list created by select

List<int> lst = Orders.where(u=> u.SplOrderID != null).Select(u => (int)u.SplOrderID);

Answer 4

Useful helper / extension method :

I usually use some helper extensions method for the jobs mentioned in the other answers :

public static class IEnumerableExtensions
{
    public static IEnumerable<TKey> GetNonNull<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey?> keySelector) 
        where TKey : struct
    {
        return source.Select(keySelector)
            .Where(x => x.HasValue)
            .Select(x => x.Value);
    }

    // the two following are not needed for your example, but are handy shortcuts to be able to write : 
    // myListOfThings.GetNonNull()
    // whether myListOfThings is List<SomeClass> or List<int?> etc...
    public static IEnumerable<T> GetNonNull<T>(this IEnumerable<T?> source) where T : struct
    {
        return GetNonNull(source, x => x);
    }

    public static IEnumerable<T> GetNonNull<T>(this IEnumerable<T> source) where T : class
    {
        return GetNonNull(source, x => x);
    }

}

Usage in your case :

// will get all non-null SplOrderId in your Orders list, 
// and you can use similar syntax for any property of any object !

List<int> lst = Orders.GetNonNull(u => u.SplOrderID);

---

For the readers who don't want to simply ignore null values while converting

It's worth mentioning the potential use of GetValueOrDefault(defaultValue) yet, maybe you do you want to keep your original null values, but convert them to some default / sentinel value. (given as the defaultValue parameter) :

For your example :

// this will convert all null values to 0 (the default(int) value)
List<int> lst =
     Orders.Select(u => u.GetValueOrDefault())
     .ToList();

// but you can use your own custom default value
const int DefaultValue = -1;
List<int> lst =
     Orders.Select(u => u.GetValueOrDefault(DefaultValue))
     .ToList();