Read / write blob field
lazarus / 16-Databases

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LemonParty · 2025-09-05 15:13

Hello.

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

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cdbc · 2025-09-05 16:28

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

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LemonParty · 2025-09-05 17:51

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

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cdbc · 2025-09-05 18:05

Hi
What's in it?!?
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.btnLoadClick(Sender: TObject);var lstrm: TStream;begin  ... 
Query1.Open;  ...  lstrm:=
Query1.CreateBlobStream(Query.FieldByName('photo'),bmRead); 
lstrm.Position:= 0;  Picture1.Graphic.LoadFromStream(lstrm); 
lstrm.Free;  ...end;Regards Benny

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LemonParty · 2025-09-05 20:10

Isn't this going to work:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
ReadVar(const aVar; aSize: SizeUInt): TBytes;inline;begin 
SetLength(Result, aSize);  Move(aVar, Result[0], aSize);end; procedure
WriteVar(const B: TBytes; var aVar);inline;begin  Move(B[0], aVar,
Length(B));end;
Than used this way:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  
WriteVar(Query.FieldByName('MyBlobField').AsBytes, MyVar);  {...} 
Query.FieldByName('MyBlobField').AsBytes:= ReadVar(MyVar,
SizeOf(MyVar));

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cdbc · 2025-09-05 22:02

Hi
I think these are better:Code: Pascal  [Select][+][-]window.onload =
function(){var x1 = document.getElementById("main_content_section");
if (x1) { var x = document.getElementsByClassName("geshi");for (var i
= 0; i program bytestovar; {$mode objfpc}{$H+} uses  {$IFDEF UNIX} 
cthreads,  {$ENDIF}  Classes, sysutils  { you can add units after this
}; procedure BytesToVar(const B: TBytes; var aVar; var aSize:
sizeint); inline;begin { old win32 api trick }  if aSize < 0 then
begin aSize:= Length(B); exit; end;  Move(B[0],pointer(aVar)^,
Length(B));end; function VarToBytes(const aVar; aSize: SizeUInt):
TBytes; inline;begin  SetLength(Result, aSize);  Move(pointer(aVar)^,
Result[0], aSize);end; var  aVar,ls: string;  blob: TBytes;  b: byte; 
sz: sizeint = -1; begin  if ParamCount >= 1 then ls:= ParamStr(1) 
else begin writeln('(!) Try again with "some text" in first param.');
halt(1); end;  writeln('(i) Input.: ',ls);  blob:=
VarToBytes(ls,length(ls));  write('(i) TBytes: ');  for b in blob do
write(b.ToHexString(2),' ');  writeln;  { if we call BytesToVar with a
negative 'aSize' it will return the size needed in 'aSize' } 
BytesToVar(blob,aVar,sz); { sz was initialized to -1, but returns with
the actual size }  aVar:= StringOfChar(#0,sz); // got the size, we
have to allocate the memory beforehand  { the thing is... in
BytesToVar we have no chance of finding out the type of 'aVar' } 
BytesToVar(blob,aVar,sz);  writeln('(i) aVar..: ',aVar);end.(* The
above "Shenanigans" are old tricks from win32 API *)  Regards Benny