Question

I have a Data access library which I would like to return different data formats (XML, Json, DataTable). I was trying to use Generics to achieve this.

public interface IDBInteractor<T>
{
    T ExecuteDSQuery(string myQuery)
}

public class DBInteractorDT : IDBInteractor<DataTable>
{
    public DataTable ExecuteDSQuery(string myQuery)
    {
        return new DataTable();
    }
}

public class DBInteractorJson : IDBInteractor<JsonString>
{
    public JsonString ExecuteDSQuery(string myQuery)
    {
        return new JsonString();
    }
}

I am having trouble invoking the correct method. Ideally I would to declare something like

     SomeClass<DataTable> dt = new SomeClass<DataTable>();
     SomeClass<JsonString> js = new SomeClass<JsonString>();

     DataTable myDT = dt.ExecuteDSQuery(myQuery);
     JsonString myJson = js.ExecuteDSQuery(myQuery);

I’m not sure how to declare SomeClass. I know I could do something like

    public class SomeClass<T> where T : IDBInteractor <T>
    {
        public T ExecuteQuery(T dtobject, string myQuery)
        {
           return dtobject.ExecuteDSQuery(myQuery);
        }
    }

But I don’t want to have to pass an object instance (dtobject) to each method call.

Answer 1

What exactly are you trying to do? This code works fine:

using System.Data;

namespace ConsoleApplication7
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            IDBInteractor<DataTable> dt = new SomeClass<DataTable>(new DBInteractorDT());
            IDBInteractor<JsonString> js = new SomeClass<JsonString>(new DBInteractorJson());
            /*
            or you can write 

            IDBInteractor<DataTable> dt = new DBInteractorDT();
            IDBInteractor<JsonString> js = new DBInteractorJson();

             */

            DataTable myDT = dt.ExecuteDSQuery("");
            JsonString myJson = js.ExecuteDSQuery("");
        }
    }

    public interface IDBInteractor<T>
    {
        T ExecuteDSQuery(string myQuery);
    }

    public class DBInteractorDT : IDBInteractor<DataTable>
    {
        #region IDBInteractor<DataTable> Members

        public DataTable ExecuteDSQuery(string myQuery)
        {
            return new DataTable();
        }

        #endregion
    }

    public class DBInteractorJson : IDBInteractor<JsonString>
    {
        #region IDBInteractor<JsonString> Members

        public JsonString ExecuteDSQuery(string myQuery)
        {
            return new JsonString();
        }

        #endregion
    }

    public class SomeClass<T> : IDBInteractor<T>
    {
        private IDBInteractor<T> interactor;

        public SomeClass(IDBInteractor<T> interactor)
        {
            this.interactor = interactor;
        }

        public T ExecuteDSQuery(string myQuery)
        {
            return interactor.ExecuteDSQuery(myQuery);
        }
    }

    public class JsonString
    {
    }
}