CODEWITHSUNDEEP
delphidelphi-xe2datasnap
Raido
Raido

Reputation: 571

Datasnap and TObject references

How to handle object references in datasnap server?

I have Datasnap server method which returns TUser object

TServerMethods.CurrentUser(const AId: Integer): TUser
begin
  Result := GlobalCurrentUser; // <- Don't want to free this object
  Result.AddReference;
end;

TUser in child class of TReferencedObject

TReferencedObject = class(TObject)
private
  FReferenceCnt:     integer;
public
  procedure AddReference; virtual;
  procedure RemoveReference; virtual; // Frees object if reference count goes to 0
  property ReferenceCnt: integer Read FReferenceCnt Write FReferenceCnt;
end;

Currently DataSnap server Frees TUser object but I want to call RemoveReference for TReferencedObject descendants.

Upvotes: 1

Views: 575

Answers (1)

Raido
Raido

Reputation: 571

I copied DataSnap files Data.DBXJSONReflect.pas and Datasnap.DSReflect.pas to project directory, add to project and made three modifications.

Two changes in Data.DBXJSONReflect to set correct ReferenceCount

1) TJSONUnMarshal.CreateObject

  if HasObject(ObjId) then
  begin
    Obj := GetObject(ObjId);
    if Obj is TReferencedObject then {Framework}
      TReferencedObject(Obj).AddReference; {Framework}    
    exit(Obj);
  end

2) TJSONPopulationCustomiser.PostPopulate 

  if Data is TReferencedObject then {Framework}
    TReferencedObject(Data).AddReference; {Framework}

One change in Datasnap.DSReflect to release reference

1) TDsMethodValues.ClearReferenceParameters

changed FUserObject.Clear to ClearUserObjects(FUserObjects); and added local function

  procedure ClearUserObjects(const AUserObjects: TObjectList<TObject>); {Framework}
  var
    i: Integer;
  begin
    FUserObjects.OwnsObjects := False;
    for i := FUserObjects.Count - 1 downto 0 do
      if FUserObjects.Items[i] is TReferencedObject then
      begin
        TReferencedObject(FUserObjects.Items[i]).RemoveReference;
        FUserObjects.Delete(i);
      end;
    FUserObjects.OwnsObjects := True;
    FUserObjects.Clear;
  end;

Upvotes: 1

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