How to avoid casting between the DL - BL - UI layers ? (C#)

I designing an applications which basically has 3 different logic layers:

1. DB connector (implemented by ADO.NET).
2. BL the business logic (the only thing the UI knows).
3. DB repositories (connects between the first two).

The DB repositories are separated into sections of dependency and every final entity is polymorphic to one interface. In some cases there are dependencies between objects inside the same dependency sections - ISectionFactory (hence dependent). In practice the BL is going to ask for an object of specific type (such as IngrediantType in my example) from the MainFactory (which is a factor for all the DB) Because of this design I am forced to cast types on the UI - which obviously is a drag. How can I change the design ? Here is a brief look of design:

public class MainFactory
{
    private Dictionary<Type, ISectionFactory> m_SectionsFactories;
    private ISectionFactory treatmentsSectionFactory = 
            new TreatmentsSectionFactory();

    public MainFactory()
    {
        m_SectionsFactories = new Dictionary<Type, ISectionFactory>
            {
                {typeof(IngrediantType),treatmentsSectionFactory}
            };
    }

    public IConcreteDataCollection GetConcreteData(Type i_EntitiesName)
    {
        return m_SectionsFactories[i_EntitiesName]
            .GetConcre开发者_开发知识库teData(i_EntitiesName);
    }
}

internal interface ISectionFactory
{
    IConcreteDataCollection GetConcreteData(Type i_EntitiesName);
}

public class TreatmentsSectionFactory : ISectionFactory
{
    private Dictionary<Type, IConcreteDataCollection> 
            m_ConcreteDataCollections;

    private IngrediantTypes m_IngrediantTypes = new IngrediantTypes();
    private Ingrediants m_Ingrediants = new Ingrediants();

    public TreatmentsSectionFactory()
    {
        m_ConcreteDataCollections = 
            new Dictionary<Type, IConcreteDataCollection>();
        m_ConcreteDataCollections
            .Add(typeof(IngrediantType), m_IngrediantTypes);
        m_ConcreteDataCollections
            .Add(typeof(Ingrediants), m_Ingrediants);
    }

    public IConcreteDataCollection GetConcreteData(Type i_EntitiesName)
    {
        return m_ConcreteDataCollections[i_EntitiesName];
    }
}

public interface IConcreteDataCollection : IEnumerable
{
    // Iteratable.
    IConcreteData GetById(int i_Id);
    void AddNewConcreteData(IConcreteData i_ConcreteData);
    void UppdateConcreteData(IConcreteData i_ConcreteData);
    void DeleteConcreteData(IConcreteData i_ConcreteToDelete);
}

public class IngrediantTypes : IConcreteDataCollection
{
    public string TestType { get; set; }
    public IConcreteData GetById(int i_Id){}
    public void AddNewConcreteData(IConcreteData i_ConcreteData){}
    public void UppdateConcreteData(IConcreteData i_ConcreteData){}
    public void DeleteConcreteData(IConcreteData i_ConcreteToDelete){}        
    public IEnumerator GetEnumerator(){}
}

// also implements IConcreteDataCollection
public class Ingrediants : IConcreteDataCollection 
{
}

public interface IConcreteData
{
    public int Index { set; get; }        
} // the final (highest) entity of all DB entities

public class IngrediantType : IConcreteData
{
    public int Index { set; get; }
    // other set of properties
}

public class Ingrediant : IConcreteData
{
    public int Index { set; get; }
    public IngrediantType RelatedIngrediantType { set; get; }
    // other set of properties
}

public class mainClass
{
    public static void main()
    {
        MainFactory factory = new MainFactory();

        var type = typeof(IngrediantType);

        // returns a IngrdiantTypes of type (IConcreteDataCollection)
        var t = factory.GetConcreteData(typeof(IngrediantType)); 

        // I want to use the IngrediantType without casting !!!
        var s = t.GetById(2); 
    }
}

It's a little hard to tell what's going on here, but I think the key will be to take advantage of generics like so:

public IConcreteDataCollection<T> GetConcreteData<T>()
{
    return ...;
}

If I understand your question correctly, this will allow you to say:

var t = factory.GetConcreteData<IngrediantType>(); 

You will need to change almost every class in your code to use generics.