MS Access/ru

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Этот перевод скопирован со страницы User:QLKforges/ru

Эта страница объясняет, как использовать базу данных Microsoft Access с использованием ODBC и FPC в SQLdb.

Специфика MS Access

UsePrimaryKeyAsKey

В свойствах TSQLQuery, возможно, потребуется установить UsePrimaryKeyAsKey: False

Get just-inserted autonumber primary key

After inserting data, Access 2000 and higher supports getting the just-inserted autonumber primary key using this query: 

SELECT @@IDENTITY

ODBC Драйвер

Windows

Есть 2 различных ODBC драйвера для Microsoft Access:

  • Старый драйвер, который можно использовать только формат файла .mdb, называется он "Microsoft Access Driver (*.mdb)". В многих версиях Windows (начиная с Windows 2000, вплоть до Vista); Для более старых версий Windows нужно загрузить 32-х битные компоненты такие, как MDAC или Jet.
  • Новый драйвер, который может получить доступ как .mdb и .accdb файлам, называется "Microsoft Access Driver (*.mdb, * .accdb)". Доступен как в 32-х битной так, и 64-х битной "Microsoft Access Database Engine 2010 Redistributable";.

Как обычно, при использовании 32 бит Lazarus / FPC, использовать 32 водителей немного ODBC. При использовании 64-битной Lazarus / FPC, использовать 64 водителей немного ODBC. Редактируется

Unix/Linux

The mdbtools project offers limited support for MS Accesss. It includes an ODBC driver which might be used. Try installing packages like mdbtools mdbtools-dev mdbtools-gmdb

At least on Debian, the ODBC driver name is "MDBTools".

File-based DSN Instructions

A file DSN is simply where the connection settings are written to a file. The reason for having a file DSN is if you want to distribute a data source connection to multiple users on different systems without having to configure a DSN for each system. For instance, I can create a file DSN to a reporting database on my desktop. I can then send the file to my users. My users can save the file DSN to their hard drives and then point their reporting applications at the file DSN.

If you want to use a file-based DSN with the SQLDB ODBC driver:

Set up the File DSN

  • Go to your [Data sources (ODBC)] at the control panel administrative tools.
  • Go to [File DSN] tab menu, Click Add, then Select <microsoft access driver>.
  • Next, browse to your current Lazarus project path to save your .DSN file, because that dsn file will contain the configuration needed to access your database file (.mdb).
  • Click Next, then Finish (you now have created a new .dsn file) of which will be use in your TODBCConnection [FileDSN].

File DSN contents

For reference, a file DSN that refers to an MS Access database may look something like this: 

[ODBC]
DRIVER=Microsoft Access Driver (*.mdb)
UID=admin
UserCommitSync=Yes
Threads=3
SafeTransactions=0
PageTimeout=5
MaxScanRows=8
MaxBufferSize=2048
FIL=MS Access
DriverId=25
DefaultDir=
DBQ=YOUR_msaccess.mdb

Configure your project to use file-based DSN

Usage of grids and other data bound controls is the same as for any other SQLDB connector, so that is not covered here.

As you're using an ODBC connection, you should have a TODBCConnection object.

TOBDCConnection Properties: FileDSN: the path+filename to the DSN file saved earlier, e.g. c:\mylazarus\project1\myFile.dsn Username: admin (or whatever username you need if you are using Access security) this parameter may not be needed if no MS Access security is used Do not put any other entries in the properties.


System/User DSN

As explained in the ODBC article, you can also use system or user DSNs, where connection settings are defined in the ODBC control panel instead of stored in a file.

The TODBCConnection should have DatabaseName: <name_of_your_DSN>

DSN-less connection

As explained in the ODBC article, you can also create a DSN-less connection to your Access database where you can specify all connection parameters in code, something like: 

  //Notice we're using the new MS Access driver, we could probably use the old one too:
  conn.Driver:='Microsoft Access Driver (*.mdb, *.accdb)';
  conn.Params.Add('DBQ=c:\somedirectory\test.mdb');
  ... add whatever parameters you want/need...


Example code

Lazarus: data bound controls on forms

Working Source code sample:(Updated2_with_add_delete_update) http://www.mediafire.com/file/ne1jx3zpnwzefq3/msaccesstest2.zip 

unit Unit1; 

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, odbcconn, sqldb, db, FileUtil, LResources, Forms, Controls,
  Graphics, Dialogs, DBGrids, DbCtrls, StdCtrls, Printers, PrintersDlgs;

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Datasource1: TDatasource;
    DBEdit1: TDBEdit;
    DBEdit2: TDBEdit;
    DBGrid1: TDBGrid;
    ODBCConnection1: TODBCConnection;
    PrintDialog1: TPrintDialog;
    SQLQuery1: TSQLQuery;
    SQLTransaction1: TSQLTransaction;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure FormCloseQuery(Sender: TObject; var CanClose: boolean);
    procedure FormShow(Sender: TObject);
  private
    { private declarations }
    procedure PrintDbGrid(dbGrid:TdbGrid);
  public
    { public declarations }
  end; 

var
  Form1: TForm1; 

implementation

{ TForm1 }

procedure TForm1.FormShow(Sender: TObject);
begin
  //connection
  ODBCConnection1.FileDSN := ExtractFilePath(Application.ExeName) + 'file.dsn';
  ODBCConnection1.Connected := True;
  ODBCConnection1.KeepConnection := True;

  //transaction
  SQLTransaction1.DataBase := ODBCConnection1;
  SQLTransaction1.Action := caCommit;
  SQLTransaction1.Active := True; //not applied to ms access(false)

  SQLQuery1.DataBase := ODBCConnection1;
  SQLQuery1.UsePrimaryKeyAsKey := False;

  SQLQuery1.SQL.Text := 'select * from table1';

  // :id is the parameter for the field name id
  SQLQuery1.deleteSQL.Text := 'delete from table1 where id=:id';
  //:name is the parameter for the field name name
  SQLQuery1.updateSQL.Text := 'update table1 set name=:name where id=:id';

  DataSource1.DataSet := SQLQuery1;
  DBGrid1.DataSource := DataSource1;
  DBGrid1.ReadOnly := true;

  DBEdit1.DataField := 'id';
  DBEdit1.DataSource := DataSource1;
  DBEdit2.DataField := 'name';
  DBEdit2.DataSource := DataSource1;

  SQLQuery1.Open;
end;

function MulDiv(nNumber, nNumerator, nDenominator: Integer): Integer;
begin
  Result:=Round(int64(nNumber)*int64(nNumerator)/nDenominator);
end;
procedure TForm1.PrintDbGrid(dbGrid:TdbGrid);
const
  LeftMargin = 0.05;
  TopMargin = 0.05;
  BottomMargin = 0.05;
var
  i: integer;
  x,y: integer;
begin
  if PrintDialog1.Execute then
    begin
    Printer.BeginDoc;
    Printer.Canvas.Font.Size := 12;

    y := Round(TopMargin*Printer.PageHeight);
    dbGrid.DataSource.DataSet.First;
    while not dbGrid.DataSource.DataSet.Eof do
      begin
      x := Round(LeftMargin*Printer.PageWidth);
      for i := 0 to dbGrid.DataSource.DataSet.FieldCount-1 do
        begin
        printer.Canvas.TextOut(x,y,dbGrid.DataSource.DataSet.Fields[i].AsString);
        x := x + MulDiv(dbGrid.Columns[i].Width,72, dbGrid.Width);
        end;
      dbGrid.DataSource.DataSet.Next;
      y := y + printer.Canvas.TextHeight('A');
      if y > (1-TopMargin-BottomMargin)* Printer.PageHeight then
        begin
        y := Round(TopMargin*Printer.PageHeight);
        Printer.NewPage;
        end;
      end;
    Printer.EndDoc;
    end
    else
    Form1.caption := 'NO PRINTER INSTALLED';
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  PrintDbGrid(DBGrid1);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
if button2.Caption = 'new' then
begin
  SQLQuery1.Insert;
  button2.Caption := 'save';
  exit
  end
  else
  begin
    if (dbedit1.Text = '') or (dbedit2.Text = '')
    then
    begin
    SQLQuery1.Cancel;
    end
    else
    begin
    if SQLQuery1.State = dsInsert then
       begin
       SQLQuery1.Post;
       SQLQuery1.ApplyUpdates;
       Form1.caption := 'ADDED';
       end;
    end;
  end;
button2.Caption := 'new';
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
if SQLQuery1.RecordCount>0 then
  begin
  SQLQuery1.Delete;
  SQLQuery1.ApplyUpdates;

  //REMOVED or ADD this 2 lines if there is a problem in your SQLdB
  //THESE 2 lines apparently work around a bug in SQLdB for MS_Access dataBase'
  //**** missing reference to bugtracker item; please create a bugtracker item
  //SQLQuery1.Close;
  //SQLQuery1.Open;


  Form1.caption := 'DELETED';
  end;
end;

procedure TForm1.Button4Click(Sender: TObject);
begin
  if SQLQuery1.RecordCount>0 then
  begin
    SQLQuery1.Edit;
    SQLQuery1.Post;
    Sqlquery1.ApplyUpdates;
    Form1.caption := 'UPDATED';
  end;
end;

procedure TForm1.FormCloseQuery(Sender: TObject; var CanClose: boolean);
begin
  SQLQuery1.Close;
  CanClose := True;
end;

initialization
  {$I unit1.lrs}

end.

Create a database programmatically

Using either ODBC driver, you can programmatically create Microsoft Access databases. (Note: error handling has not been tested; please update page if you tested it)

Example program: 

program CreateAccessDb;

{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
  Classes, sysutils,
  Windows;

Const
   ODBC_ADD_DSN=1;
   ODBC_CONFIG_DSN=2;
   ODBC_REMOVE_DSN=3;
   ODBC_ADD_SYS_DSN=4;
   ODBC_CONFIG_SYS_DSN=5;
   ODBC_REMOVE_SYS_DSN=6;
   ODBC_REMOVE_DEFAULT_DSN=7;
function SQLConfigDataSource(hwndParent: Integer; fRequest: Integer;
  lpszDriverString: PChar; lpszAttributes: PChar): Integer; stdcall; external 'odbccp32.dll';
function SQLInstallerError(iError: integer; pfErrorCode: PInteger; lpszErrorMsg: string; cbErrorMsgMax: integer; pcbErrorMsg: PInteger): integer; stdcall; external 'odbccp32.dll';

function CreateAccessDatabase(DatabaseFile: string): boolean;
var
  DBPChar: PChar;
  Driver: PChar;
  ErrorCode, ResizeErrorMessage: integer;
  ErrorMessage: PChar;
  retCode: integer;
begin
	driver := 'Microsoft Access Driver (*.mdb, *.accdb)';
  { With this driver,
  CREATE_DB/CREATE_DBV12 will create an .accdb format database;
  CREATE_DBV4 will create an mdb
  http://stackoverflow.com/questions/9205633/how-do-i-specify-the-odbc-access-driver-format-when-creating-the-database
  }
  DBPChar:=PChar('CREATE_DBV4="'+DatabaseFile+'"');
  retCode := SQLConfigDataSource(Hwnd(nil), ODBC_ADD_DSN, Driver, DBPChar);
  if retCode<>0 then
  begin
    //try alternate driver
    Driver := 'Microsoft Access Driver (*.mdb)';
    DBPChar:=PChar('CREATE_DB="'+DatabaseFile+'"');
    retCode := SQLConfigDataSource(Hwnd(nil), ODBC_ADD_DSN, Driver, DBPChar);
  end;
  if retCode=0 then
  begin
    result:=true;
  end
  else
  begin
    result:=false;
    ErrorCode:=0;
    ResizeErrorMessage:=0;
    // todo: verify how the DLL is called - use pointers?; has not been tested.
    GetMem(ErrorMessage,512);
    try
      SQLInstallerError(1, @ErrorCode, ErrorMessage, SizeOf(ErrorMessage), @ResizeErrorMessage);
    finally
      FreeMem(ErrorMessage);
    end;
    raise Exception.CreateFmt('Error creating Access database: %s', [ErrorMessage]);
  end;
end;

begin
  writeln('Result: ');
  write(CreateAccessDatabase('d:\cop\t\bla.mdb'));
end.

Example database

Microsoft Access ships with the Northwind example database.

If you only have the Access Runtime installed, you can use this alternative database from the Mondial project as a test database: [1]

See also

  • ODBCConn The ODBC connector this article uses
Retrieved from "https://wiki.freepascal.org/index.php?title=MS_Access/ru&oldid=132692"