Question

I just can’t figure out how to write an equivalent interface in c#.

Java:

public interface DAO {
    <T> T find(Class<T> c, Object key);

    <T> List<T> get(Class<T> c);

    <T> void persist(T object);
}

This is my attempt so far in c#, problem is i need the Class to call the dataclassesdatacontext.GetTable<Class here>().ToList();:

interface IDAO
{
    T Find<T>(object key);

    List<T> Get<T>(T c);

    void Persist<T>(T obj);
}

I want to implement it like this:

public List<T> Get<T>()
{
return _dbx.GetTable<T>().ToList();
}


where _dbx is the dataclassdatacontext (linq to sql).
But i get a red line under T which says:
The type ‘T’ must be a reference type in order to use it as a parameter.

Answer 1

What you are looking for are Generic constraints. Namely you need to add where T : class to methods with T parameter.

And like Darin Dimitrov said, it might be good idea to set type for whole interface, not every method. This will result in cleaner desing.