List<> of objects, different types, sort and pull out types individually?

I've got a handful of products, any, all, or none of which may be associated with a specific submission. All 7 products are subclasses of the class Product. I need to store all the products associated with a submission, and then retrieve them and their field data on my presentation layer. I've been using a List<Product>, and List<object>, but when I use the OfType<EPL(specific subclass)>, I throw an error saying that I can't implicitly convert systems.generic.IEnumerable<EPL> to type 'Product'. I've tried to cast, but to no avail.

When I use prodlist.OfType<EPL>(); there are no errors, but when I try and store that in an instance of EPL "tempEpl", I get the aforementioned cast-related error. What gives? Code below.

 ProductService pserv = new ProductService();
    IList<object> prodlist = pserv.getProductById(x);

    EPL tempEpl = new EPL();

    if ((prodlist.OfType<EPL>()) != null)
    {            
       tempEpl = prodlist.OfType<EPL>();  // this throws a conversion error. 

    }

the Data layer

List<object> TempProdList = new List<object>();

    conn.Open();

    SqlCommand EplCmd = new SqlCommand(EPLQuery, conn);
    SqlDataReader EplRead = null;
    EplRead = EplCmd.ExecuteReader();

    EPL TempEpl = new EPL();
    if (EplRead.Read()) 
    {

        TempEpl.Entity1 = EplRead.GetString(0);
        TempEpl.Employees1 = EplRead.GetInt32(1);
        TempEpl.CA1 = EplRead.GetInt32(2);
        TempEpl.MI1 = EplRead.GetInt32(3);
        TempEpl.NY1 = EplRead.GetInt32(4);
        TempEpl.NJ1 = EplRead.GetInt32(5);
        TempEpl.PrimEx1 = EplRead.GetInt32(6);
        TempEpl.EplLim1 = EplRead.GetInt32(7);
        TempEpl.E开发者_如何学PythonplSir1 = EplRead.GetInt32(8);
        TempEpl.Premium1 = EplRead.GetInt32(9);
        TempEpl.Wage1 = EplRead.GetInt32(10);
        TempEpl.Sublim1 = EplRead.GetInt32(11);

        TempProdList.Add(TempEpl);
    }

This code makes no sense:

Product tempEpl = new EPL();

if ((prodlist.OfType<EPL>()) != null)
{            
   prodlist.OfType<EPL>();
}

• It's unclear why you're creating a new EPL() to start with
• OfType() will never return null - it returns a sequence, which may be empty
• Calling OfType() won't do anything useful on its own, as per the body of your if statement

It's important to understand that OfType() returns a sequence, not a single item. I suspect that's what you were missing before.

I suspect you want:

Product tempEpl = prodList.OfType<EPL>().FirstOrDefault();

This will assign a value of null to tempEpl if there are no elements of type EPL in prodList, or the first EPL element in the list otherwise.

(It's not clear why you're returning a List<object> from the data layer to start with. Why not a List<Product>?)

I think in DAL instead of returning a list of Object type you should return a list of Product type. If you do so then there is no need for casting it to Product type again.

Second thing, in the PL, instead of using IList just use List.