Accept method to return null - C# .NET MVC

Question

I am building a little application in .NET 4 MVC 2 for the office foosball table. I have this repository with a method summing all the values of one column (decimal) using LINQ to SQL. It looks like this:

public decimal GetPlayerRating(int id)
{
    var playerRating = (from r in db.Ratings
                        where r.PlayerID == id
                        select r.Points).Sum();

    return playerRating;
}

The problem is that sometimes when it's called it returns null because the given player does not have any records in the table. That's fine -- in that case it should just return zero. But I get this error:

The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.InvalidOperationException: The null value cannot be assigned to a member with type System.Decimal which is a non-nullable value type.

How can I tell my method that it is okay to return a null value? Thanks!

asawyer · Accepted Answer · 2011-03-09 16:17:55Z

7

Try the null coalese operator

return playerRating ?? 0d;

That will never return a null.

If you really need to return a nullable valuetype, though try this

public decimal? GetPlayerRating(int id)
{ ... }

Adding a ? to the end of a value type like double is rewritten into Nullable < type > (Nullable < double > here)

When dealing with a nullable value type, be sure to check if it has a value (not null)

if ( myNullableType.HasValue ) 
{
    x = myNullableType.Value;
}

answered Mar 9, 2011 at 16:17

asawyer

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2 Comments

Sebastian Brandes Over a year ago

Thanks a lot for your quick answer. It worked! The thing is that I am calling this method from my controller where I am calculating the team rating (two players' respective ratings combined). In retrospect, returning null from my repository might not be the best solution. I think it will be better to return a simple zero. How do I do that when a given player has no records in the table and, thus, his rating sum is null? (I hope that made sense.)

asawyer Over a year ago

Np, Your best bet is to file a new SO question for this though.

Vishal · Accepted Answer · 2011-03-09 16:20:16Z

0

public decimal GetPlayerRating(int id)
{
    return db.Ratings.Where(r=>r.PlayerID == id).Select(r=>r.Points).Sum() ?? 0;

}

Or Change your return type to decimal? to get it working..

answered Mar 9, 2011 at 16:20

Vishal

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