What is the difference between suffixes Service, Manager, System?

Question

I'm curious about the difference between Service, Manager and System.

All the time I tried to avoid such suffixes. But after I started working with MVC, I needed to create a separate class so as not to access the controller every time from any script to invoke a function. I was prompted to use the Service class to refer to it from any script. And as I understood using controllers as separate entities only for handling events (Did I understand correctly?): How to use a controller from another controller in MVC

From the example on the link above, I have a SpeakerController which accepting an events and directing it to SpeakerService that performs certain functions.

Why it was necessary to name SpeakerService, and not just Speaker? From the names of the OOP principle, I have always seen only a noun for the class without suffixes.

I expect a more readable program where the name speaks for itself. I have tried using the Manager and Service suffixes but I don't understand their conceptual necessity

Answer 1

When we write software, we need a way to separate classes. If we put all classes in one folder/project, it would be a complete mess. So almost all programs have to:

• save state/data somewhere. It can be database. We want to create classes for mapping, e.g. SQL tables to POCO classes. Let's call this layer as Model.
• apply some business rules model. This layer brings together managers or methods to finish a complete task such as E.g. Calculate the nearest distance between cities or make a coffee from many ingredients. Let's call this layer as Service.
• show handled data by business rules to user. Let's call this layer as View.

So for me:

• services should be used to assemble multiple managers to finish a complete task.
• managers are used to apply some business logic for one concrete model. E.g. UserManager for Chat System can have the following methods such as GetUserById, GetOnlineUsers(), AddUser(), UserLogin(), UserLogoff()

UPDATE:

I saw services offen in ASP.NET MVC. So this is a simple example:

This is a model:

public class Blog
{
    public string Name { get; set; }

    public IEnumerable<Post> Posts { get; set; }

    public IEnumerable<Comment> Comments { get; set; }
}

And view models:

public class BlogViewModel
{
    public string Name { get; set; }

    public IEnumerable<PostViewModel> Posts { get; set; }

    public IEnumerable<CommentViewModel> Comments { get; set; }
}   

These are repositories:

public interface IPostRepository
{
    IEnumerable<Post> GetById();
}

public interface ICommentRepository
{
    IEnumerable<Comment> GetById();
}

public interface IBlogRepository
{
    IEnumerable<Blog> GetById();
}   

and our service:

public class BlogService
{
    IPostRepository _postRepository;
    ICommentRepository _commentRepository;
    IBlogRepository _blogRepository;

    public BlogService(IPostRepository postRepository, 
        ICommentRepository commentRepository, IBlogRepository blogRepository)
    {
        _postRepository = postRepository;
        _commentRepository = commentRepository;
        _blogRepository = blogRepository;
    }

    // here a place to accomplish the whole task
    public BlogViewModel Get()
    {
        BlogViewModel blogViewModel = new BlogViewModel();
        blogViewModel.Comments = _mapper.Map<IEnumerable<CommentViewModel>>(
            _commentRepository.GetById());
        blogViewModel.Posts = _mapper.Map<IEnumerable<PostViewModel>>(
            _postRepository.GetById());
        return new BlogViewModel();
    }        
}

and controller method:

public BlogViewModel Get() 
{
    return _blogService.Get();
}   

An example of using manager

Let's create a chat application. The oop model could look like this:

User class:

public class User
{
    public string FirstName { get; set; }

    public string LastName { get; set; }

    public string NickName { get; set; }

    public Status Status { get; set; }

    IEnumerable<Topic> Topics { get; set; }
}

Message class:

public class Message 
{
    public int Id { get; set; }

    public string Content { get; set; }

    public DateTime DateCreated { get; set; }
}

Topic class:

public class Topic
{
    public IEnumerable<User> Participants { get; set; }

    public IEnumerable<Message> Messages { get; set; }

    public void AddMessage(Message message) { }

    public void RemoveMessage(int id) { }

    public void AlterMessage(Message message) { }

    public void AddUser(User user) { }

    public void RemoveUser(int id) { }

    public void BlockUser(User user) { }

    public void InviteUser(User user) { }
}

Status enum:

public enum Status { 
    Online, 
    Busy, 
    Available
}

ChatSystem class:

public class ChatSystem
{
    public IEnumerable<Topic> Topics { get; set; }

    public void AddTopic(Topic topic) { }

    public void RemoveTopic(int id) { }

    public void AlterTopic(Topic topic) { }

    public void Login(string email, string password) { }
    public void Logoff() { }

}

UserManager class:

public class UserManager
{
    public IEnumerable<User> AllUsers { get; set; }

    public User GetById() 
    { 
        return new User(); 
    }

    public Status GetUserStatus()
    {
        return new User().Status;
    }

    public void AddUser(User user) { }

    public void RemoveUser(User user) { }

    public void SendEmail(User user) { }
}