Read / write blob field

[LemonParty]

Hello.

How to read / write a blob field to my variable?

[cdbc]

Hi
What kind of blob?!?
If it is text, then you can use the new features in my 'IStringList', which you can find HERE.
...and attached is a demo-app for sqlite3, which amo. deals with memo-blobs... And it shows how to use the new features of 'IStringList' 
Regards Benny

[LemonParty]

I use SQLite and have a field declared as Blob. It is not string.

[cdbc]

Hi
What's in it?!?

Code: Pascal  [Select][+][-]

1. procedure TForm1.btnLoadClick(Sender: TObject);
2. var lstrm: TStream;
3. begin
4.   ...
5.   Query1.Open;
6.   ...
7.   lstrm:= Query1.CreateBlobStream(Query.FieldByName('photo'),bmRead);
8.   lstrm.Position:= 0;
9.   Picture1.Graphic.LoadFromStream(lstrm);
10.   lstrm.Free;
11.   ...
12. end;

Regards Benny

[LemonParty]

Isn't this going to work:

Code: Pascal  [Select][+][-]

1. function ReadVar(const aVar; aSize: SizeUInt): TBytes;inline;
2. begin
3.   SetLength(Result, aSize);
4.   Move(aVar, Result[0], aSize);
5. end;
6.  
7. procedure WriteVar(const B: TBytes; var aVar);inline;
8. begin
9.   Move(B[0], aVar, Length(B));
10. end;

Than used this way:

Code: Pascal  [Select][+][-]

1.   WriteVar(Query.FieldByName('MyBlobField').AsBytes, MyVar);
2.   {...}
3.   Query.FieldByName('MyBlobField').AsBytes:= ReadVar(MyVar, SizeOf(MyVar));
4.  

[cdbc]

Hi
I think these are better:

Code: Pascal  [Select][+][-]

1. program bytestovar;
2.  
3. {$mode objfpc}{$H+}
4.  
5. uses
6.   {$IFDEF UNIX}
7.   cthreads,
8.   {$ENDIF}
9.   Classes, sysutils
10.   { you can add units after this };
11.  
12. procedure BytesToVar(const B: TBytes; var aVar; var aSize: sizeint); inline;
13. begin { old win32 api trick }
14.   if aSize < 0 then begin aSize:= Length(B); exit; end;
15.   Move(B[0],pointer(aVar)^, Length(B));
16. end;
17.  
18. function VarToBytes(const aVar; aSize: SizeUInt): TBytes; inline;
19. begin
20.   SetLength(Result, aSize);
21.   Move(pointer(aVar)^, Result[0], aSize);
22. end;
23.  
24. var
25.   aVar,ls: string;
26.   blob: TBytes;
27.   b: byte;
28.   sz: sizeint = -1;
29.  
30. begin
31.   if ParamCount >= 1 then ls:= ParamStr(1)
32.   else begin writeln('(!) Try again with "some text" in first param.'); halt(1); end;
33.   writeln('(i) Input.: ',ls);
34.   blob:= VarToBytes(ls,length(ls));
35.   write('(i) TBytes: ');
36.   for b in blob do write(b.ToHexString(2),' ');
37.   writeln;
38.   { if we call BytesToVar with a negative 'aSize' it will return the size needed in 'aSize' }
39.   BytesToVar(blob,aVar,sz); { sz was initialized to -1, but returns with the actual size }
40.   aVar:= StringOfChar(#0,sz); // got the size, we have to allocate the memory beforehand
41.   { the thing is... in BytesToVar we have no chance of finding out the type of 'aVar' }
42.   BytesToVar(blob,aVar,sz);
43.   writeln('(i) aVar..: ',aVar);
44. end.
45. (* The above "Shenanigans" are old tricks from win32 API *)  

Regards Benny