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sakura

Member

From: Germany

Registered: 2018-02-21

Posts: 228

Website

DDD Many-To-Many mapping to SQLRecords

Hi,

I have the following simple SQL Records:

  TSQLBook = class;
  TSQLAuthor = class;

  TSQLLinkBookAuthor = class(TSQLRecordMany)
  protected
    FSource: TSQLBook;
    FDest: TSQLAuthor;
  published
    property Source: TSQLBook read FSource write FSource;
    property Dest: TSQLAuthor read FDest write FDest;
  end;

  TSQLBook = class(TSQLRecord)
  protected
    FTitle: RawUTF8;
    FDesc: RawUTF8;
    FAuthorList: TSQLLinkBookAuthor;
  published
    property Title: RawUTF8 read FTitle write FTitle;
    property Desc: RawUTF8 read FDesc write FDesc;
    property AuthorList: TSQLLinkBookAuthor read FAuthorList;
  end;

  TSQLAuthor = class(TSQLRecord)
  protected
    FName: RawUTF8;
    FBookList: TSQLLinkBookAuthor;
  published
    property Name: RawUTF8 read FName write FName;
    property BookList: TSQLLinkBookAuthor read FBookList;
  end;

In my Domain-Classes, what type do I need to use for the links? See -->

type
  TBook = class;
  TAuthor = class;

  TLinkBookAuthor = class(TUkiSynAutoCreateFields)
  private
    FSource: TBook;
    FDest: TAuthor;
  protected
    procedure AssignTo(aDest: TSynPersistent); override;
  public
    constructor Create; override;
    destructor Destroy; override;
  published
    property Source: TBook read FSource write FSource;
    property Dest: TAuthor read FDest write FDest;
  end;
  TLinkBookAuthorObjArray = array of TLinkBookAuthor;

  TBook = class(TUkiSynAutoCreateFields)
  private
    FTitle: RawUTF8;
    FDesc: RawUTF8;
-->    FAuthorList: TLinkBookAuthorObjArray;
  published
    property Title: RawUTF8 read FTitle write FTitle;
    property Desc: RawUTF8 read FDesc write FDesc;
-->    property AuthorList: TLinkBookAuthorObjArray read FAuthorList;
  end;

...

Kind regards,
Daniel

ab

Administrator

From: France

Registered: 2010-06-21

Posts: 14,242

Website

Re: DDD Many-To-Many mapping to SQLRecords

DDD many-to-many mapping is indeed made with T*ObjArray - which need registration.
But they will be stored as a JSON array in the database, not a JOINed table.

DDD favors aggregates, not RDBMS and table joins.
You are starting from the DB - i.e. the TSQLRecord - which is the wrong way of doing it in DDD.
Start from the objects, define the aggregate scope, then store your aggregate as a whole.
This is how DDD works.