Question Simple CRUD application to learn the n-tier architecture

[Matthieu]

Hi everyone!
I want to use the n-layer architecture for a very simple CRUD console application. I have a domain layer, presentation layer (a console application), a business layer and a data acces layer.
If I'm right, the DAL is used to interact with a database, and the BL is a layer between the PL and the DAL.

So for exampe, if I have a database with a 'Persons' table and each record consists out of a firstname and lastname.
Imagine in my console application I create an option 'add person to database' or something like that.
the console application asks the user to fill in a firstname and a lastname.
it's the BL that takes the user input from the PL and gives it to the DAL, right?

To become familiar with the whole n-layer architecture, I created a very, VERY, simple console application.
The console application can show a user all records in the 'Persons' table and can let a user add a record to the 'Persons' table.

First things first, I created a 'Person' class in the domain layer:

public class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
       
        public Person(string firstName, string lastName)
        {
            FirstName = firstName;
            LastName = lastName;
        }
       
        public override string ToString()
        {
            return $"{FirstName} {LastName}";
        }
    }

In the DAL I created a PersonRepository class with a few methods to interact with the database that stores the 'Persons' table. Cause at the moment I don't know how to interact with a database, I created a list containing Person objects to represent the 'Persons' table. I have a static method Seed() to fill the list with dummy data:

public class PersonRepository
    {
        private static readonly List<Person> _persons = new List<Person>();

        static PersonRepository()
        {
            Seed();
        }

        public Person ReadPerson(string firstName, string lastName)
        {
            return _persons.Find(p =>
                p.FirstName.ToLower() == firstName.ToLower() && p.LastName.ToLower() == lastName.ToLower());
        }

        public IEnumerable<Person> ReadPersons()
        {
            return _persons;
        }

        public void CreatePerson(Person person)
        {
            _persons.Add(person);
        }
       
        public static void Seed()
        {
            Person person1 = new Person("Anakin","Skywalker");
            _persons.Add(person1);
            Person person2 = new Person("Luke","Skywalker");
            _persons.Add(person2);
        }
    }

In the BL I created a PersonManager class that take user input from the presentation layer and let it interact with the DAL:

public class PersonManager
    {
        private readonly PersonRepository _personRepository = new PersonRepository();

        public Person GetPerson(string firstName, string lastName)
        {
            return _personRepository.ReadPerson(firstName, lastName);
        }

        public IEnumerable<Person> GetPersons()
        {
            return _personRepository.ReadPersons();
        }

        public void AddPerson(Person person)
        {
           Person p =  _personRepository.ReadPerson(person.FirstName, person.LastName);
           if (p == null)
           {
             _personRepository.CreatePerson(person);
           }
           else
           {
               throw new ArgumentException("A person with that first- and lastname already exists!");
           }
        }
    }

An lastly, I created a console application to let a user decide which he/she want's to do:

class Program
    {
        private static readonly PersonManager _personManager = new PersonManager();

        static void Main(string[] args)
        {
            bool quit = false;
            do
            {
                Console.WriteLine("0) Quit");
                Console.WriteLine("1) View all persons");
                Console.WriteLine("2) Create person");
                Console.Write("Choice:");
                int choice;
                bool parseSucces = Int32.TryParse(Console.ReadLine(), out choice);
                if (parseSucces)
                {
                    switch (choice)
                    {
                        case 0:
                            quit = true;
                            break;
                        case 1:
                            Console.WriteLine($"\nAll persons:");
                            foreach (var p in _personManager.GetPersons())
                            {
                                Console.WriteLine($"\t -{p.FirstName} {p.LastName}");
                            }
                            break;
                        case 2:
                            Console.Write($"\nFirstname:");
                            string firstName = Console.ReadLine();
                            Console.Write("Lastname:");
                            string lastName = Console.ReadLine();
                            try
                            {
                                _personManager.AddPerson(new Person(firstName,lastName));
                            }
                            catch (Exception e)
                            {
                                Console.WriteLine($"\n{e.Message}");
                            }

                            break;
                    }
                }
                else
                {
                    Console.WriteLine("Please, enter a number!");
                }

                Console.WriteLine();
            } while (!quit);
           
        }
    }

I'm think i'm using the repository-service pattern. So can I say repository-service pattern can be used in the n-tier achitecture or...?

Thanks!

 

[Skydiver]

Here's my take on this: N-tier architecture just requires that your app be built in layers. The repository-services pattern dictates that your business logic be split into layers. Therefore the layers requirement is satisfied.

 

[Matthieu]

Here's my take on this: N-tier architecture just requires that your app be built in layers. The repository-services pattern dictates that your business logic be split into layers. Therefore the layers requirement is satisfied.

Alriht, thanks! So in theory the example I made is a correct n-tier application?