Delphi Load Blob from MySql - mysql

Question

in my project i use mysql.pas to deal with MySql database , so i've this Table structure :
Table Name :CarsTbl
ID int 10
CarName varchar 100
Car_Img longblob 0
i use this table to save each Car with its name and its picture .
The save routine works very well .
But the problem is when getting the Car_Img in which i use the following procedure :
procedure GetCarImage(const MyCarName:String;TrgStream:TMemoryStream);
var
query_string: String;
rCount: Integer;
mySQL_Res: PMYSQL_RES;
LibH: PMYSQL;
Row: PMYSQL_ROW;
iLen:PMYSQL_LENGTHS;
begin
mySQL_Res := nil;
Try
Try
query_string := 'SELECT CarName,Car_Img FROM CarsTbl WHERE CarName="'+MyCarName+'"';
mysql_real_query(LibH, PAnsiChar(query_string), Length(query_string));
mySQL_Res := mysql_store_result(LibH);
Try
rCount := mysql_num_rows(mySQL_Res);
If rCount > 0 Then Begin
Repeat
Row := mysql_fetch_row(mySQL_Res);
iLen:= mysql_fetch_lengths(mySQL_Res);
If Row <> nil Then Begin
TrgStream.position :=0;
//Row^[1] ==== Car_Img Blob Field
TrgStream.WriteBuffer(Row^[1],iLen[1]);
End;
Until Row = nil;
end;
Finally
mysql_free_result(mySQL_Res);
mySQL_Res := nil;
Row := nil;
End;
Finally
mysql_close(LibH);
End;
Finally
LibH := nil;
End;
end;
I get the Car image but with Malformed file Header let me explain :
Audi_Car image is saved as a Png image , but when i Load its image i always get it like this :
So please how could correct this ? is there any error in my Sql query ?
P.S : i create TrgStream in an other place.
And here's my LoadCarImage Procedure :
Procedure LoadCarImage();
var
CarStrm:TMemoryStream;
begin
CarStrm:=TMemoryStream.Create;
Try
GetCarImage('Audi',CarStrm);
CarStrm.SaveToFile('audi.png');
finally
CarStrm.Free;
end;
end;
many thanks

Answer 1

you should not use
Repeat ... until
CarName is not unique. So if you have more than one Audi in your table you create also a not valid image file.
Try it with
Delphi5
EDIT:
With
TrgStream.WriteBuffer(Row^[1],iLen[1]);
WriteBuffer takes the first pointer and writing the content of the whole Row.
In your .png file now you have
ID00CarName00Car_Img
9Wî00f­î00Audi00‰PNG.......
I prefer the long way via the array only to see what I get.
Now that you have tested it. we have found no error in the writing of the present stream.
we use instead of
TrgStream.WriteBuffer(Row^[1],iLen[1]);
this
TrgStream.WriteBuffer(Row^[1]^,iLen[1]);
procedure GetCarImage(const MyCarName:String;TrgStream:TMemoryStream);
var
[...]
begin
[...]
query_string := 'SELECT CarName,Car_Img FROM cars WHERE CarName="Audi"';
mysql_real_query(LibH, PAnsiChar(query_string), Length(query_string));
mySQL_Res := mysql_store_result(LibH);
Try
rCount := mysql_num_rows(mySQL_Res);
If rCount > 0 Then Begin
Row := mysql_fetch_row(mySQL_Res);
iLen:= mysql_fetch_lengths(mySQL_Res);
If Row <> nil Then Begin
TrgStream.position :=0;
//Row^[1] ==== Car_Img Blob Field
TrgStream.WriteBuffer(Row^[1]^,iLen[1]);
[...]

Answer 2

I had the allmost same problem.
I wanted read emf (picture metafile) from mysql glob field.
And I solved it like this.
var
text_t1:string;
Stream: TStream;
begin
text_t1:='';
text_t1:=' select emf_glob from table ';
ADOQuery1.Close;
ADOQuery1.SQL.Clear;
ADOQuery1.SQL.Add(text_t1);
ADOQuery1.Open;
ADOQuery1.first;
Stream:= TMemoryStream.Create;
Stream := ADOQuery1.CreateBlobStream(ADOQuery1.FieldByName('emf_glob'), bmRead);
Stream.Position:=0;
DBImage1.Picture.LoadFromStream(Stream);
Stream.Free;