Question

Is there a single-line way of casting an object to a decimal? data type?

My code looks something like this:

foreach(DataRow row in dt.Rows)
{
    var a = new ClassA()
    {
         PropertyA = row["ValueA"] as decimal?,   
         PropertyB = row["ValueB"] as decimal?,
         PropertyC = row["ValueC"] as decimal?
    };

    // Do something

}

However casting an object to a decimal? doesn’t work the way I expect it to, and returns null every time.

The data rows are read from an Excel file, so the data type of the object in each row is either a double if there is a value, or a null string if it’s left blank.

The suggested method to perform this cast is to use decimal.TryParse, however I do not want to create a temp variable for every decimal property on the class (I have about 7 properties on my actual class that are decimals, not 3).

decimal tmpvalue;
decimal? result = decimal.TryParse((string)value, out tmpvalue) ?
                  tmpvalue : (decimal?)null;

Is there a way I can cast a potentially null value to a decimal? in a single line?

I tried the answer posted here, however it doesn’t appear to be working and gives me a null value as well because row["ValueA"] as string returns null.

Answer 1

providing there is a value it reads as a double, otherwise I think it’s a string

Okay, so this complicates matters as sometimes you need to parse it and sometimes you don’t.

The first thing we’ll want to do is check if it’s already a double and cast it, because casting is much cheaper than parsing; parsing is expensive.

Given that this logic will be non-trivial, it belongs in it’s own method:

public static deciaml? getDecimal(object rawValue)
{
    decimal finalValue;

    double? doubleValue = rawValue as double?;
    if(doubleValue.HasValue)
        return (decimal) doubleValue.Value;
    else if(decimal.TryParse(rawValue as string, out finalValue))
    {
        return finalValue;
    }
    else
    {
        return null;//could also throw an exception if you wanted.
    }
}

If you know that it will always be a double, and you’ll never want the string values, then it’s easier still. In that case you need to cast it to a double, first, since that’s it’s real type, and then you can easily convert it to a decimal:

PropertyA = (decimal?)(row["ValueA"] as double?);