Migrate Data from one class to a second class [duplicate] - delphi

Question

This question already has answers here:
Copy object data fields into subclass instance
(2 answers)
Closed 8 years ago.
depending on the dataflow (data itself) i'm starting with a very simple data type "AboutMe", later depending on the data itself or the workflow I want to continue working using this data now in a class called "AboutMe_more". This procedure might happen 1..3 times in my program.
AboutMe= class
Name : String
end;
AboutMe_more = class(AboutMe)
gender : String;
Birth : TDate;
Aboutme_complete = class (AboutMe_more)
adresss : String;
salery : Real;
.....
end;
starting with the complete class is not a good idea in my case because there might be a different switch to an other desired class like
Aboutme_complete_option = class (AboutMe_more)
company : string;
city : String;
kids : String;
.....
end;
Q:
a) What is the best way to transfer data from one class to the derived class, not need for transfer data to parent class .
b) Is the way a good programming style or does the need for that datamovement indicate a poor class construction / design ?

Answer 1

It almost looks like you are trying to model a database using objects.
b) Is the way a good programming style or does the need for that datamovement indicate a poor class construction / design ?
The problem here (as mentioned by #jpfollenius) is that you'll end up with a very deep hierarchy of objects.
a) What is the best way to transfer data from one class to the derived class [...]?
I don't know about the best way, but in Delphi transferring data from one object to another is often done using an overloaded Assign.
TMyObject = class(TPersistent)
procedure Assign(Source: TPersistent); overload;
....
implementation
procedure TMyObject.Assign(Source: TPersistent);
begin
inherited Assign(Source);
if (Source is TMyObject) then begin
Self.Field1:= Source.Field1;
Self.Field2:= Source.Field2;
end;
end;
More sensible approach
Inheritance is only one way to address this problem.
A more appropriate way would be to use encapsulation.
Here you have an object and an interface which holds the data and container objects which give you access to that data.
Delphi has a very nice mechanism for that because it allows you to delegate the implementation of an interface to a contained object.
An example using 2 data objects with interfaces and a container object.
type
IData1 = interface
['{3F996D68-1FD0-4490-AE60-8F735A9DFFE8}'] //Use ctrl+alt+g to generate a number
function GetData1: integer;
procedure SetData1(value: integer);
property Data1: integer read GetData1 write SetData1;
end;
IData2 = interface
['{3F996D68-1FD0-4490-AE60-8F735A9DFFE9}']
function GetData2: integer;
procedure SetData2(value: integer);
property Data2: integer read GetData2 write SetData2;
end;
TData1 = class(TInterfacedObject, IData1);
private
FData1: integer;
protected
function GetData1: integer;
procedure SetData1(value: integer);
public
property Data: integer read GetData1 write SetData1;
end;
TData2 = class(TInterfacedObject, IData2);
{see TData1 above}
TContainer = class(TInterfacedObject, IData1, IData2)
private
FData1: TData1;
FData2: TData2;
public
constructor Create();
property Data1: TData1 read FData1 implements IData1; //delegates implementation to object FData.
property Data2: TData2 read FData2 implements IData2;
end;
Copied from this question: https://stackoverflow.com/questions/6063274/hidden-features-in-the-delphi-language (now sadly deleted).