Connect to mysql inside dll

aamoaa · Post by **aamoaa** » Fri 27 Nov 2009 02:09

Hi ,

For example, I have a main unit of the program.

this unit call dll library the dll include connection to the database in the form and other code .

When i close the application i write this in formclose

Code: Select all

procedure Tfr_sell_buy.FormClose (Sender: TObject; var Action: TCloseAction);
begin
MyConnection1.Connected: = false;
MyConnection1.Free;
Action: = caFree;
end;

Now I can close the application with out problem.

Problem if i add a connection object MyConnection1 on the main unit or just adding myaccess to uses in the main unit.
When application is terminated i found it still i manager task.
and i can not freelibrary it also return me error .

How i Solved it .

i used trial mydac 5.90 for d2010
Thank you

Dimon · Post by **Dimon** » Fri 27 Nov 2009 08:17

This problem is connected with work with dll, but not with MyDAC. The point is that you create the TMyConnection class object in an application and use it in a dll. Methods of TMyConnection use the "as" operator which returns error.

To solve the problem you can use the TCustomMyConnection.AssignConnect method to assign the TMyConnection object created in application to the TMyConnection object of dll.
Also you can use the approach used in the MyDAC DLL demo. You can find this demo by the following path: MyDAC_InstDir\Demos\Miscellaneous\Dll.
MyDAC_InstDir is the MyDAC installation directory on your computer.

aamoaa · Post by **aamoaa** » Sat 28 Nov 2009 15:53

Same Problem in your your Demos\dll

I'm thinking to use the class (TThread) to connection . THis way good or not

Dimon · Post by **Dimon** » Mon 30 Nov 2009 07:37

Please, specify exact steps to reproduce the problem.

aamoaa · Post by **aamoaa** » Mon 30 Nov 2009 23:59

Hi,

Code: Select all

library aacol;
uses
  SysUtils, Classes, myaccess, mydacvcl, IniFiles;
var con : TMyConnection ;
    myq_m : TMyQuery ;
    myq_d : TMyQuery ;
{$R *.res}
//----------------------------------------
function F_cusname : TStringList ;
var i : Integer ;
begin
//------------
con := TMyConnection.Create(nil);
myq_m := TMyQuery.Create(nil);
myq_d := TMyQuery.Create(nil);
Result := TStringList.Create ;
    with con do
      begin
      Server := 'localhost';
      Database := 'aa';
      Username := 'root';
      Password := '11';
      LoginPrompt := false ;
      Options.UseUnicode := true ;
      Connect ;
      end;
with myq_m do
begin
  Connection := con ;
  SQL.Clear ;
  SQL.Add('select * from customers') ;
  open ;
  first ;
  for I := 0 to recordcount-1 do
    begin
      Result.Add(FieldByName('cus_name').AsString) ;
      next ;
    end;
  Close ;
  end;
con.Disconnect ;
con.Free ;
myq_m.Free ;
myq_d.Free ;
end;
//------------
exports F_cusname ;
end.

Code: Select all

var  F_cusname: function : TStringList  ;
  st  : TStringList ;
begin
  st := TStringList.Create ;
  DLLhandle := LoadLibrary(aacol.dll');
  @F_cusname := GetProcAddress(DLLhandle, 'F_cusname');
  st := F_cusname ;
  for I := 0 to st.Count - 1 do ComboBox1.Items.Add(st[i]);
  FreeLibrary(DLLhandle) ;

Show the error .

Dimon · Post by **Dimon** » Tue 01 Dec 2009 09:05

The problem is arised because the exported "F_cusname" function returns a TStringList object. To solve the problem use a procedural type (like in the MyDAC DLL demo) instead of "function: TStringList"