DDD - Dependencies between domain model, services and repositories

Question

Just wanted to know how others have layered their architecture. Say I have my layers as follows:

Domain Layer
--Product
--ProductService (Should the imp go

Answer 1

In agreement with Marcelo, you should probably first determine if the product ID is really a domain model concept. If the business users never use or have any idea of the product ID and usually refer to the product by name, number, SKU or a natural product ID made up of name + dimensions, then this is what the domain model should be aware of.

That being said, here is how I structure my DDD projects assuming that the product ID is an auto-number field in the database:

Project.Business (Domain Model)

No references and therefore, no dependencies upon anything.

public class Product : Entity
{
    private Product(string name, Address address)
    {
        //set values.
    }

    //Factory method, even for simple ctor is used for encapsulation so we don't have 
    //to publically expose the constructor.  What if we needed more than just a couple           
    //of value objects?
    public static CreateNewProduct(string name, Address address) 
    {
        return new Product(name, address);
    }

    public static GetAddress(string address, string city, string state, string zip) { }
}

public interface IProductRepository : IEnumerable
{
    void Add(Product product);
    //The following methods are extraneous, but included for completion sake.
    int IndexOf(Product product);
    Product this[int index] { get; set; }
}

Project.Implementation

public SqlProductRepository : List, IProductRepository
{
    public SqlProductRepository(string sqlConnectionString) { }

    public void Add(Product product)
    {
        //Get new Id and save the product to the db.
    }

    public int IndexOf(Product product)
    {
        //Get the index of the base class and convert to business object.
    }

    public Product this[int index]
    {
        get { //find instance based on index and return; }
        set { //find product ID based on index and save the passed in Business object to the database under that ID. }
    }
}

Project.ApplicationName (Presentation Layer)

public class Application
{
    IProductRepository repository = new SqlProductRepository(SqlConnectionString);

    protected void Save_Click(object sender, EventArgs e)
    {
        Product newProduct = Product.CreateNewProduct(name, Product.GetAddress(address,city,state,zip));
        repository.Add(newProduct);
    }
}    

If necessary, you may have:

Project.Services (Application Services Layer that uses DTOs between itself and the Presentation Layer)