Unable to Get data from DA layer. What to do?

Answer 1

One of the reasons people do Persistance Ignorant objects (POCO) is to avoid such a scenario. There is simply no way for the data access layer to have a reference to a class that it doesn't know about - it is much better to have the class not know about the data access.

The only way you can really do this is to implement Get() on User instead of on UserDA. You can do something like this:

public class User {
  IGetFromPresistance<User> _userFetcher;
  public static IList<User> GetMatching(Specification<User> spec) {
    var values = _userFetcher.Find(spec);  //Returns a DataRow or IDictionary<string, object>
    return new User() {
      PhoneNumber = new PhoneNumber(values["phone"].ToString()),
      Name = values["name"].ToString(),
    };
  }
}

Answer 2

As far as I can understand you have a bidirectional relationship between your DA and Business layer. To solve this problem I suggest that you should have 3 layers instead of two. I mean you should have a Model layer that simply model the DB objects ,then you can derive from model classes in your Business layer and add other behaviors like Save method.

Here's what I mean:

//Model Layer
public class UserModel
{
public virtual string Firstname{get;set;}
}
//DataAccess Layer
public class UserDao
{
List<UserModel> GetAll();
}
//BusinessLayer
public class UserDomainModel:UserModel
{
public UserDomainModel(UserModel user,UserDao dao)
{
_user=user;
_dao=dao;
}
public override string FirstName
{
get
{
return _user.FirstName;
}
set
{
_user.FirstName=value;
}

public void Save()
{
_dao.Save(_user);
}
}
}

I'm using a decorator to combine User and UserDao as a domain model object.