Where are the Delphi Attributes Real World Examples?

Question

I know by TMS Aurelius that we can use the \"new\" 2010 attributes feature to serialize database table fields into object properties at run-time, for example, and I am not an ex

Answer 1

I must say it's not much clear to me what kind of example do you need. IMHO in http://docwiki.embarcadero.com/RADStudio/Rio/en/Overview_of_Attributes is everything you should need, perhaps providing that you have some basic knowledge of annotation and/or aspect programming resp.

An example depends on the way/purpose an author of particular SW used attributes for. You mentioned the ORM system: the typical usage here is to annotate member of the class representing DB entity with additional information necessary for DB operation in the backend of such framework. Let assume you have a DB entity having field COMPANY CHAR(32) NOT NULL and you want to represent it in Delphi class:

TSomeDBEntity = class(...)
  FCDS: TClientDataset;
  ...
  constructor Create;
  ... 
  [TCharColumn('COMPANY', 32, false)]
  property CompanyName: string read GetCompanyName write SetCompanyName;
end;

then you will define attribute TCharColumn with constructor

constructor TCharColumn.Create(const AFieldName:string; ALength:integer; ANullable:boolean);
begin
  inherited;
  FName := AFieldName;
  FLength := ALength;
  FNullable := ANullable;
end;

And usage of such annotation could look something like this:

FCDS := TClientDataset.Create(nil);
RttiContext := TRttiContext.Create;
try
  RttiType := RttiContext.GetType(self.ClassType);
  Props := RttiType.GetProperties;
  for Prop in Props do
    begin
      Attrs := Prop.GetAttributes;
      case Prop.PropertyType.TypeKind of
        tkUString:
          begin
            for Attr in Attrs do
              if Attr is TCharColumn then
              begin
                ColAttr := TCharColumn(Attr);
                FCDS.FieldDefs.Add(ColAttr.FName, ftString, ColAttr.FLength, not ColAttr.FNullable);
              end;
          end;
        else
          //... ;
      end;
    end;
finally
  RttiContext.Free;
end;

This piece of the program demonstrates, how to define fields in a dataset in run-time based on annotation in Delphi. We are limited little bit due lack of named parameters, hence working with parameter list is not flexible as should be e.g. like in Java (compare TMS Aurelius annotation set http://www.tmssoftware.com/site/manuals/aurelius_manual.pdf and http://www.techferry.com/articles/hibernate-jpa-annotations.html