Why can't I assign a value to a decimal with a ternary operator?

Question

I have a list of objects (using anonymous types) containing a decimal and an integer ID, and I'm building a function to take the sum of the decimals contained within all unique objects in the list.

This is the line of code I wrote:

var result = (objectList.Any()) ? objectList.Distinct().Sum(x => x.DecimalValue) : 0;

However, it always returns a decimal with the value 0 , even though it should be returning the sum - objectList contains five identical objects in my example, so it should return the DecimalValue.

If I replace it with these two lines of code, however, it returns the DecimalValue:

decimal result = 0;
if (objectList.Any()) result = objectList.Distinct().Sum(x => x.DecimalValue);

Why does the second set of lines work, but the first line returns the wrong value? objectList.Any() is true, so it shouldn't be using the false assignment.

Update: I generated the list of anonymous types using this line of code:

var objectList = _ms.Read(cmd, x => new { DecimalValue = x.Field<decimal>("SomeColumnName"), Id = x.Field<int>("SomeColumnId") }).ToList();

_ms is a DAO for MS SQL, and it's running the lambda function that converts each datarow of the results to the anonymous typed object, which is returned in a list. I actually haven't been able to figure out how to build a list of those objects manually.

Another Update: Using Reed Copsey's reply below, I created the list manually in a way that duplicates the list that I'm getting, and I can reproduce the error with the manually created list:

var objectList = Enumerable.Range(0, 5).Select(i => new { DecimalValue = (decimal)31.45, Id = 3 }).ToList();
var result = (objectList.Any()) ? objectList.Distinct().Sum(x => x.DecimalValue) : 0;

I also tried removing the cast to decimal, and the issue is still present.

Another Update: After some further debugging I realized something I've never come across before. I set a breakpoint immediately after the line of code I mentioned that was having problems in each case. For the workaround, it returned 31.45. For the problem line, it returned 0. When I stepped into the next line, and looked at the variable again, it said 31.45. The line I set the breakpoint on did not access or modify the variable.

It would seem that both lines work, but that the debugger showed that it did not until I moved at least two lines after the code. I've never come across that before, but it shows that the code indeed does work.

Answer 1

There is no problem with your statement.

The issue is elsewhere, most likely in how you're constructing objectList .

For example, the following works exactly as expected, and prints "0.6" (as would be expected):

namespace Test
{
    using System;
    using System.Linq;

    internal class TestCompile
    {
        private static void Main(string[] args)
        {
            var objectList = Enumerable.Range(0, 3).Select(i => new { ID = i, DecimalValue = i / 5.0m }).ToList();

            decimal result = objectList.Any() ? objectList.Distinct().Sum(x => x.DecimalValue) : 0;

            Console.WriteLine(result);
            Console.ReadKey();
        }
    }
}

---

Update:

In response to your update, this also works perfectly:

private static void Main(string[] args)
{
    var objectList = Enumerable.Range(0, 5).Select(i => new { DecimalValue = (decimal)31.45, Id = 3 }).ToList();
    var result = (objectList.Any()) ? objectList.Distinct().Sum(x => x.DecimalValue) : 0;

    Console.WriteLine(result);
    Console.ReadKey();
}

It is using the exact code you pasted, and reports 31.45 , as expected (due to the unique constraint). Note that, personally, I would use 31.45m instead of the cast, but it works even as written...

Answer 2

For what it's worth, your code works though I had to make up my own type.

[Test]
public void X()
{
    var objectList = Enumerable.Range(1, 10).Select(d => new {DecimalValue = Convert.ToDecimal(d)});

    var result = (objectList.Any()) ? objectList.Distinct().Sum(x => x.DecimalValue) : 0;

    Assert.AreEqual(55, result);
    Assert.AreEqual(typeof (decimal), result.GetType());
}

Too big for a comment so CW it is.

Answer 3

I just compiled a code

    public class ObjectValue
    {
        public Decimal DecimalValue { get; set; }
    }

    class Program
    {

        static void Main(string[] args)
        {
            var objectList = new List<ObjectValue>() { new ObjectValue() { DecimalValue = 5 }, new ObjectValue() { DecimalValue = 5 } ,
                    new ObjectValue() { DecimalValue = 5 }};


            var result = (objectList.Any()) ? objectList.Distinct().Sum(x => x.DecimalValue) : 0;

            decimal resultDecimal = 0;
            if (objectList.Any())
                resultDecimal = objectList.Distinct().Sum(x => x.DecimalValue);

        }
    }

And result and resultDecimal are 15 , in my case. I have coherent result in both cases provided, as I expected. So the error is somewhere else.