How to load and save properties of a TParam

[Andre van Zuydam]

Hi Everyone

I had quite a struggle today to figure this one out but in the end it 
worked.  I needed to save parameters of a query for later use but the 
TStream.WriteComponentRes only supported writing the data from objects 
inheriting from TComponent.

Here is my solution :

I created a class called TParamSave.  Notice the published property 
Params which is needed for WriteComponentRes to "save" it.


TParamSave = class(TComponent)
 private
   FParams : TParams;
 public
   constructor Create(AOwner: TComponent); override;
 published
    property Params : TParams read FParams write FParams;
end;

Under Implementation is the very basic constructor for the Params, 
otherwise we have problems later

{ TParamSave }

constructor TParamSave.Create(AOwner: TComponent);
begin
 inherited;
 Params := TParams.Create;
end;

Well all you need to do now is save it to a stream / file or database 
field.  Here is my code below, I am saving it to a database blob field 
but I tested it to files also.

var
   Stream : TStream;
   ParamSave : TParamSave;

begin
   try  
     Stream := TMemoryStream.Create;
     ParamSave := TParamSave.Create(Self);
     ParamSave.Name := 'Param';
     ParamSave.Params := ExtraParams;  //ExtraParams is my parameters 
from a query
     Stream.WriteComponentRes('Params', ParamSave);

     ......insert sql here ....

     qryQuery.ParamByName ('extraparams').LoadFromStream(Stream, ftBlob);
     qryQuery.ExecSQL;
  finally
      Stream.Free;
      ParamSave.Free;     
  end;
end;

And then finally to read it back into the application

var
 ExtraParams : TParams;
 ParamSave : TParamSave;
 Stream : TStream;

begin
 try
   Stream := TMemoryStream.Create;
   (qryBatchPrint.FieldByName('extraparams') as 
TBlobField).SaveToStream (Stream);
   ExtraParams := TParams.Create;

   ParamSave := TParamSave.Create(Self);
   Stream.Position := 0;
   Stream.ReadComponentRes (ParamSave);

   ExtraParams.Assign(ParamSave.Params);


 finally
   Stream.Free;
   ExtraParams.Free;
 end;
end;

And thats it !

I hope this helps someone else who got stuck on this issue. 


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