Another "generic" question. Coming up with BaseRepository

I'm finding that all my data repositories look alike and decided to try and make one base class with generics.

Rather than create a repository per entity type, you may want to create one per unit-of-work. Otherwise you are going to be creating a lot more work for your self than needed.

By unit of work, I mean a related set of entities. An example might be employees, the primary entity is Employee, but you also may have contacts, addresses, and other such related entities.

This is what I do:

public abstract class RepositoryBase<T> : IRepository
        where T : EntityManager
    {
    }

then I would create an IEmployeeRepository that might look like this:

public interface  IEmployeeRepository : IRepository
    {
        INotifyCompleted GetEmployee(Guid employeeId, Action<Employee> onSuccess, Action<Exception> onFail);
        INotifyCompleted GetEmployeeHistory(Guid employeeId, Action<IEnumerable<EmployeeHistory>> onSuccess, Action<Exception> onFail);
     }

    public class EmployeeRepository :RepositoryBase<MyEntities>, IEmployeeRepository
    {
        public INotifyCompleted GetEmployee(Guid employeeId, Action<Employee> onSuccess, Action<Exception> onFail)
        {

        }

        public INotifyCompleted GetEmployeeHistory(Guid employeeId, Action<IEnumerable<EmployeeHistory>> onSuccess, Action<Exception> onFail)
        {

        }
     }

DevForce Caliburn is a great framework to look at, I believe they have examples very similar to this.

One of the places I make use of the INotifyCompleted is with my Busy indicators. I might write some code like this:

Employee employee;
Busy.AddWatch();
Repository.GetEmployees(123, e => employee = e, ErrorHandler.HandleError)
                .WhenCompleted(args => Busy.RemoveWatch());

This way it's saying, no matter what the result, success or fail, I want to make sure I am executing a certain action.

Without this, you are forced to write code that looks like this:

Busy.AddWatch();
Repository.GetEmployees(123, e =>
{
   employee = e
   Busy.RemoveWatch();
},
(ex) =>
{
    ErrorHandler.HandleError(ex);
    Busy.RemoveWatch();
});