Question

I have the following function:

public T GetScalar<T>(string sql, T defaultValue, SQLParam[] sqlParams = null)
{
    DataTable dt = GetDataTable(sql, sqlParams);
    if (dt.Rows.Count == 0) return defaultValue;
    else
    {
        try
        {
            object tmp = dt.Rows[0][0];
            return (T)tmp;
        }
        catch { return defaultValue; }
    }
}

I am getting an InvalidCastException.

During debugging, I can see the value of tmp is 3, and T is of type int.

What is the problem here?

EDIT

A bit of background: This used to work in MySQL. I have now moved to SQLServer (with little effort thankfully) but this code now fails.

Answer 1

I suspect the value is actually a long, or something like that – and when you unbox, you have to unbox to the exact type (there are a few oddities around signedness and enums, but not long vs int).

You should be able to see this if you put a watch on tmp.GetType() – or just work out what type it should be from the SQL.