Question

I’m migrating an older .net application to .net 4, this migration has to be done in several stages, thats why some of the methods might seem a bit unconventional. Anyway…

What I have is a Stored Procedure (Analysis_select) returning one row with several columns with the result. If i call it with

var result = dbContext.Analysis_select(user.UserId, Year, Week);

everything is fine, i can view the data in with the debugger or display it in a grid view or something like that, so the expression and Stored Procedure really works! But the result is not compatible with the rest of the code so…

If I try to cast it to DataSet it fails, Visual Studio actually sais this is ok but when rendering on a web page it crashes

var result = (DataSet)dbContext.Analysis_select(user.UserId, Year, Week);

The error is as follows

Unable to cast object of type ‘SingleResult`1[Analysis_select]’ to type ‘System.Data.DataSet’.

I’ve read about some other conversions from linq to DataSet but most of the methods seems a bit excessive for this. The reason why I want to keep the DataSet is that there’s tens of thousands of lines of code depending on such results. Sucks yes, but can you help me fix this?

Any help is highly appreciated, thanks!

Answer 1

You will need to write an extension method to convert the IEnumerable into a DataSet. Here is an example of how to convert IEnumerable to a DataTable.

private DataTable ToDataTable<T>(List<T> items)
{
    var table = new DataTable(typeof (T).Name);

    PropertyInfo[] props = typeof (T).GetProperties(BindingFlags.Public | BindingFlags.Instance);

    foreach (PropertyInfo prop in props)
    {
        Type t = GetCoreType(prop.PropertyType);
        table.Columns.Add(prop.Name, t);
    }

    foreach (T item in items)
    {
        var values = new object[props.Length];

        for (int i = 0; i < props.Length; i++)
        {
            values[i] = props[i].GetValue(item, null);
        }

        table.Rows.Add(values);
    }

    return table;
}
public static Type GetCoreType(Type t)
{
    if (t != null && IsNullable(t))
    {
        if (!t.IsValueType)
        {
            return t;
        }
        else
        {
            return Nullable.GetUnderlyingType(t);
        }
    }
    else
    {
        return t;
    }
}
public static bool IsNullable(Type t)
{
    return !t.IsValueType || (t.IsGenericType && t.GetGenericTypeDefinition() == typeof(Nullable<>));
}

Here’s a link to the source of this solution: http://www.chinhdo.com/20090402/convert-list-to-datatable/