I'm trying to come up with a way to write a generic interface that can be implemented for multiple data stores, basically the generic type will specify the ID for the data in the data store (some of these data stores use strongly typed libraries, so you have to call something like long createNode(Node node))
For example the system we are using now, uses longs for the IDs, but if we made the transition (or use both at the same time) to something like SQL it would most likely be GUIDs. The entities a the business logic layer are pretty much set, think of it as basically a file system with a bunch of custom attributes on the nodes.
So far I tried something like this:
public interface DataThing<T>
{
T CreateThing(CustomEntity node);
CustomEntity GetThing(T ID);
}
public class LongDataThing : DataThing<long>
{
long CreateThing(CustomEntity node)
{
//...implement
}
CustomEntity GetThing(long ID)
{
//...implement
}
}
...do the same thing for GUID/Int/string...whatever
Then when it comes to instantiating the class to work with basically a factory design pattern is where I'm having problems. I thought I could do something like:
private DataThing myDataStore;
switch(config.dbtype)
{
case "longDB":
this.myDataStore = new LongDataThing();
break;
case: "stringDB":
this.myDataStore = new StringDataThing();
break;
//...etc.
}
But I can't create private DataThing myDataStore; without specifying it as long, string...etc, which means the business logic already has to know which type is being implemented instead of just asking the factory for a datastore object.
So what am I missing here? Can you not abstract out the datatype of an interface like this and have it transparent to the calling 'business logic' and figure out which implementation is desired from a config file or some other outside logic?
