Design Patterns and Useful Methods

ICommandHandler.cs

public interface ICommandHandler<TCommand> where TCommand : ICommand
{
    void Handle(TCommand command);
}

public interface ICommand
{         
}

IQueryHandler.cs

public interface IQueryHandler<TQuery, TResult> where TQuery : IQuery<TResult>
{
    TResult Handle(TQuery query);
}

public interface IQuery<TResult>
{
}

ISelect.cs

using System.Linq;

/// <summary>
/// An Interface to define a selector query that is used to return data from the database.
/// </summary>
/// <typeparam name="TIn">The type of the input to the query.</typeparam>
/// <typeparam name="TOut">The type of the output from the query.</typeparam>
public interface ISelect<in TIn, out TOut>
{
    TOut Run(IQueryable<TIn> objects);
}