Question

Simple question
I have a class say person who has as a property a member of another class say Department.
In code terms:

class person {
public string fname {get; set;}
public string lname {get; set;}
public Department d {get; set;}
}

When I load a person I have my front end web site call my business object layer which then makes a call to my data acess layer, something to this effect:

website:
Person p;
p = BOL.GetPerson(1); //call function that returns a person

And in my business object layer I simply do some business logic and call the data access layer like so:

BOL:

return DAL.GetPerson(1); //returns a person from my Data access layer

Inside my DAL i’m simply calling a stored procedure which pulls this information from a person’s table. The only thing is I dont pull the department data because its a rather large structure…

So my question is how can i lazy load this department object in my get property WITHOUT my object knowing or calling the Business Object layer. In addition, i think it is bad practice to tightly couple a Department object with the BOL object.

In other words I DONT want to do this in my person class:

public Department d {
  get 
     {
      if(d==null)
           {
            d = BOL.GetDepartmentInfo();
           }
     }
  set 
       {
        //some code
        }

That is a person class should only contain relevant information about a person, so it really should not know about the Business object layer.

How can I solve this problem?

Edit

Here is the property:

public FunctionalGroup Department
{
    get
    {
        if (Department == null)
        {
            Department = GetDepartment();
        }
    }
    set
    {
        Department = value;
    }
}

public Action<FunctionalGroup> GetDepartment { private get; set; }

This complains that Delegate Action does not take 0 arguments

I tried calling it from the BOL like so:

//assume already have an employee object
 e.GetDepartment = (id) => BOL.GetFunctionalGroup(e.FunctionalGroupID);

Edit 2nd time

Basically here is what I have:

 private FunctionalGroup _d = null;

        public FunctionalGroup Department
        {
            get
            {
                if (_d == null)
                {
                    _d = GetDepartment();
                }
                return _d;
            }
            set
            {
                _d = value;
            }
        }

//        public Action<string, FunctionalGroup> GetDepartment { private get; set; }

        public Func<FunctionalGroup> GetDepartment { private get; set; }

My BOL class is trying to assign to this:

e.Department = (id) => BOL.GetFunctionalGroup(e.FunctionalGroupID);

My BOL class says:

public static FunctionalGroup GetFunctionalGroup(string fgID)
 {
  return DAL.GetFunctionalGroup(fgID);
 }

My DAL looks like this:

  /// <summary>
        /// Returns a functional group object along with all of its properties, otherwise null.
        /// </summary>
        /// <param name="fgID">String representation of a functional group (ex: "A-AD-C")</param>
        /// <returns>Functional group object with all associated properties, otherwise null.</returns>
        public static FunctionalGroup GetFunctionalGroup(string fgID)
        {
            FunctionalGroup fg = null;

            if (fgID.Length != 0)
            {
                  //connString = the string of our database app found in the resource file
                using (SqlConnection con = new SqlConnection(connString))
                {
                    using (SqlCommand cmd = new SqlCommand("EMPDLL_selFunctionalGroupByFunctionalGroupID", con))
                    {
                        cmd.CommandType = CommandType.StoredProcedure;
                        cmd.Parameters.Add("@FunctionalGroupID", SqlDbType.VarChar).Value = fgID;
                        con.Open();

                        using (SqlDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.HasRows)
                            {
                                if (reader.Read())
                                {
                                    //found a func group
                                    fg = new FunctionalGroup((string)reader["FunctionalGroupID"],
                                                             (long)reader["ClientID"],
                                                             (string)reader["CostCenter"],
                                                             (string)reader["Description"],
                                                             (string)reader["Comments"],
                                                             (string)reader["AddedBy"],
                                                              reader["DateAdded"] == DBNull.Value ? null : (DateTime?)reader["DateAdded"],
                                                             (string)reader["ModifiedBy"],
                                                             reader["DateModified"] == DBNull.Value ? null : (DateTime?)reader["DateModified"],
                                                             (bool)reader["Inactive"]);
                                }
                            }
                        }
                    }
                }
            }
            return fg;
        }

Final Edit

Ended up using my BOl with this:

e.GetDepartment = () => BOL.GetFunctionalGroup(e.FunctionalGroupID);

And my employee class with this:

 private FunctionalGroup _d = null;

        public FunctionalGroup Department
        {
            get
            {
                if (_d == null)
                {
                    _d = GetDepartment();
                }
                return _d;
            }
            set
            {
                _d = value;
            }
        }

        public Func<FunctionalGroup> GetDepartment { private get; set; }

Answer 1

You can give the person object a callback method that can load the department for that person:

class person {

  private Department _department = null;

  public Func<Department> GetDepartment { private get; set; }

  public string fname { get; set; }
  public string lname { get; set; }

  public Department d {
    get {
      if (_department == null) {
        _department = GetDepartment();
      }
      return _department;
    }
  }

}

When you get the person object in the business layer:

p.GetDepartment = () => BOL.GetDepartment(1);