[SOLVED] How to display image from DB in DBGrid?
lazarus / 16-Databases

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Vodnik · 2019-09-24 19:57

USERS table in Informix DB that I'm working with have AVATAR column.
It is of type BYTE and size 2147483647.
Attached is screenshot how WinSQL shows it as "Raw data" (other tabs
do not work).
Being saved to file, it successfully opens as BMP.
...Well, it would be nice to show this avatar picture in DBGrid.
Following discussion provides a solution for displaying external
files:
https://forum.lazarus.freepascal.org/index.php?topic=43467.0
But how to display image from DB in DBGrid?
(I have no graphic experience yet)

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winni · 2019-09-24 20:55

Hi!

The simple and slowest solution is this way:

Save your raw data to a temporary file
Create a TBitmap
Load the file into this bitmap
Compute your destination rectangle on the canvas of the DBGrid
Do a Bitmap.Stretchdraw on the DBGrid.canvas
Free the bitmap
delete the temporary file
done

For a faster handling there might be a way to get the raw data into a
memorystream and put it into the bitmap. But I have no idea how to do.

Winni

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paweld · 2019-09-25 04:11

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.DBGrid1DrawColumnCell(Sender: TObject; const Rect: TRect; 
DataCol: Integer; Column: TColumn; State: TGridDrawState);var  pic:
TPicture;  foto : TMemoryStream;begin  if Column.Index=2 then  begin 
 pic:=TPicture.Create;        foto:=TMemoryStream.Create;    try     
   foto.CopyFrom(SQLQuery1.CreateBlobStream(SQLQuery1.FieldByName('AVA
TAR'), bmRead), 0);      pic.LoadFromStream(foto);     
DBGrid1.Canvas.Draw(Rect.left, Rect.Top, pic);    finally     
pic.Free;          foto.Free;    end;  end;end;

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Vodnik · 2019-09-30 15:14

@paweld, thank you for the idea!

Though I didn't succeeded with it yet:

1. I replaced TPicture with TBitmap, because DBGridUsers.Canvas.Draw
expects TGraphic, not TPicture:

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
TMainForm.DBGridUsersDrawColumnCell(Sender: TObject;  const Rect:
TRect; DataCol: Integer; Column: TColumn; State: TGridDrawState);var 
bmp: TBitmap;  foto : TMemoryStream;begin  if
Column.FieldName='avatar' then  begin    foto:=TMemoryStream.Create; 
 bmp:=TBitmap.Create;    try      foto.CopyFrom(SQLQuery.CreateBlobStr
eam(SQLQuery.FieldByName('avatar'), bmRead), 0);     
bmp.LoadFromStream(foto);      DBGridUsers.Canvas.Draw(Rect.left,
Rect.Top, bmp);    finally      bmp.Free;      foto.Free;    end; 
end;end; 
2. This function call raises exception class 'External: SIGSEGV':

foto.CopyFrom(SQLQuery.CreateBlobStream(SQLQuery.FieldByName('avatar')
, bmRead), 0);

What may be the reason for that?

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Vodnik · 2019-09-30 18:18

Well, from docs:
https://www.freepascal.org/docs-
html/fcl/db/tdataset.createblobstream.html


CreateBlobStream is not intended for use by application programmers.
It creates a stream object which can be used to read or write data
from a blob field. Instead, application programmers should use the
TBlobField.LoadFromStream and TBlobField.SaveToStream methods when
reading and writing data from/to BLOB fields


Do somebody have a very simple example of using these functions?

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GAN · 2019-09-30 19:27

Quote from: Vodnik on September 30, 2019, 08:18:08 pmWell, from docs:
https://www.freepascal.org/docs-
html/fcl/db/tdataset.createblobstream.html


CreateBlobStream is not intended for use by application programmers.
It creates a stream object which can be used to read or write data
from a blob field. Instead, application programmers should use the
TBlobField.LoadFromStream and TBlobField.SaveToStream methods when
reading and writing data from/to BLOB fields


Do somebody have a very simple example of using these functions?
Sure, this works for me. I use Zeos Lib but I think the result must be
the same.

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
TfrmBancos.btnAplicaClick(Sender: TObject);var 
ms:TMemoryStream;begin  DMBcos.ZQBancos.Insert; 
DMBcos.ZQBancos.FieldByName('nombre').AsString:=edNombre.Text; 
//...rest of fields  if (logotipo.Picture.Width>0) then    begin     
ms:=TMemoryStream.Create;      Logotipo.Picture.SaveToStream(ms);    
ms.Position:=0;     
TBlobField(DMBcos.ZQBancos.FieldByName('logo')).LoadFromStream(ms);  
  ms.Free;    end  else    begin     
DMBcos.ZQBancos.FieldByName('logo').AsString:='';    end; 
DMBcos.ZQBancos.Post;  //...end;   [/quote]

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Vodnik · 2019-10-01 22:04

Thanks, GAN!
Now my procedure looks like:
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
TMainForm.DBGridUsersDrawColumnCell(Sender: TObject;  const Rect:
TRect; DataCol: Integer; Column: TColumn; State: TGridDrawState);var 
bmp: TBitmap;  foto : TMemoryStream;begin  if
Column.FieldName='avatar' then  begin    foto:=TMemoryStream.Create; 
 bmp:=TBitmap.Create;    try     
TBlobField(SQLQuery.FieldByName('avatar')).SaveToStream(foto);     
bmp.LoadFromStream(foto);      DBGridUsers.Canvas.Draw(Rect.left,
Rect.Top, bmp);    finally      bmp.Free;      foto.Free;    end; 
end;end; There are no errors reported now, but there are also no
pictures in the cells. Column 'Avatar' just shows text (blob) in each
row.
I also tried to draw just a rectangle in a cell 'Avatar'. Procedure
fires, but result is the same.
Is there any hint how the drawable column should be defined?

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wp · 2019-10-01 22:37

Maybe you must reset the stream (foto.Position := 0) after reading the
image from the DB and before loading it into the bmp:

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
TMainForm.DBGridUsersDrawColumnCell(Sender: TObject;  const Rect:
TRect; DataCol: Integer; Column: TColumn; State: TGridDrawState);var 
bmp: TBitmap;  foto : TMemoryStream;begin  if
Column.FieldName='avatar' then  begin    foto:=TMemoryStream.Create; 
 bmp:=TBitmap.Create;    try     
TBlobField(SQLQuery.FieldByName('avatar')).SaveToStream(foto);  //
stream is at the end here      foto.Position := 0;  // rewind the
stream to the start      bmp.LoadFromStream(foto);     
DBGridUsers.Canvas.Draw(Rect.left, Rect.Top, bmp);    finally     
bmp.Free;      foto.Free;    end;  end;end;

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Vodnik · 2019-10-02 07:49

@wp, thanks a lot, now it works!