delphi - 压缩 Access 数据库

Question

我正在尝试压缩 Microsoft Access 数据库，但下面显示的代码不起作用。

procedure TForm1.Disconnect1Click(Sender: TObject);
begin
  ADODataSet1.Active := False;
  ADOTable1.Active := False;
  ADODataSet1.Connection := nil;
  DataSource1.Enabled := False;
  ADOConnection1.Connected := False;
  JetEngine1.Disconnect;
end;

function DatabaseCompact(const sdbName: WideString): boolean;
{ Compact ADO mdb disconnected database. }
var
  iJetEngine: TJetEngine; { Jet Engine }
  iTempDatabase: WideString; { TEMP database }
  iTempConn: WideString; { Connection string }
const
  iProvider = 'Provider=Microsoft.Jet.OLEDB.4.0; Data Source=';
begin
  Result := False;
  iTempDatabase := ExtractFileDir(sdbName) + 'TEMP' + ExtractFileName(sdbName);
  iTempConn := iProvider + iTempDatabase;
  if FileExists(iTempDatabase) then
    DeleteFile(iTempDatabase);
  iJetEngine := TJetEngine.Create(Application);
  try
    try
      iJetEngine.CompactDatabase(iProvider + sdbName, iTempConn);
      DeleteFile(sdbName);
      RenameFile(iTempDatabase, sdbName);
    except
      on E: Exception do
        ShowMessage(E.Message);
    end;
  finally
    iJetEngine.FreeOnRelease;
    Result := True;
  end;
end;

procedure TForm1.Compact1Click(Sender: TObject);
var
  iResult: Integer;
begin
  AdvTaskDialog1.Clear;
  AdvTaskDialog1.Title := 'Compact Database';
  AdvTaskDialog1.Instruction := 'Compact Database';
  AdvTaskDialog1.Content := 'Compact the database?';
  AdvTaskDialog1.Icon := tiQuestion;
  AdvTaskDialog1.CommonButtons := [cbYes, cbNo];
  iResult := AdvTaskDialog1.Execute;
  if iResult = mrYes then
  begin
    Screen.Cursor := crHourglass;
    try
      DatabaseCompact('D:\RadProjects10\EBook Database\EBook Database.mdb');
      ADODataSet1.Connection := ADOConnection1;
      ADOConnection1.Connected := True;
    finally
      Screen.Cursor := crDefault;
    end;
  end;
end;

procedure TForm1.Connect1Click(Sender: TObject);
begin
  ADOConnection1.ConnectionString := 'Provider=Microsoft.Jet.OLEDB.4.0;' +
    'User ID=Admin;' +
    'Data Source=D:\RadProjects10\EBook Database\EBook Database.mdb;' +
    'Mode=Share Deny None;' + 'Jet OLEDB:System database="";' +
    'Jet OLEDB:Registry Path="";' + 'Jet OLEDB:Database Password="";' +
    'Jet OLEDB:Engine Type=5;' + 'Jet OLEDB:Database Locking Mode=1;' +
    'Jet OLEDB:Global Partial Bulk Ops=2;' +
    'Jet OLEDB:Global Bulk Transactions=1;' +
    'Jet OLEDB:New Database Password="";' +
    'Jet OLEDB:Create System Database=False;' +
    'Jet OLEDB:Encrypt Database=False;' +
    'Jet OLEDB:Don''t Copy Locale on Compact=False;' +
    'Jet OLEDB:Compact Without Replica Repair=False;' + 'Jet OLEDB:SFP=False;';
  ADODataSet1.Connection := ADOConnection1;
  ADOConnection1.Connected := True;
  ADODataSet1.Active := True;
  ADOTable1.Active := True;
  DataSource1.Enabled := True;
end;

即使我在压缩之前断开数据库连接，我也会收到一条错误消息:

You attempted to open a database that is already opened exclusively by the user 'Admin' on the machine 'xxxx'. Try again when the database is available.

我断开连接然后进行压缩，但出现了问题。我知道压缩 Access 数据库是件好事，因此我尝试使用我编写的用于存储联系信息的小型应用程序来实现此目的。

显然我用来断开数据库连接的代码不起作用。我哪里失败了？

Answer 1

关闭 TADOConnection 和与其关联的所有数据集后，您需要确保数据库已解锁。请记住，其他用户可能连接到数据库，在这种情况下，您无法压缩它。

在实际压缩数据库之前，您必须给喷射引擎一些时间来实际关闭连接、刷新并解锁数据库。然后测试数据库是否被锁定(尝试打开以独占使用)。

这是我使用的方法，它一直对我有用:

uses ComObj;

procedure JroRefreshCache(ADOConnection: TADOConnection);
var
  JetEngine: OleVariant;
begin
  if not ADOConnection.Connected then Exit;
  JetEngine := CreateOleObject('jro.JetEngine');
  JetEngine.RefreshCache(ADOConnection.ConnectionObject);
end;

procedure JroCompactDatabase(const Source, Destination: string);
var
  JetEngine: OleVariant;
begin
  JetEngine := CreateOleObject('jro.JetEngine');
  JetEngine.CompactDatabase(
    'Provider=Microsoft.Jet.OLEDB.4.0;Data Source=' + Source,
    'Provider=Microsoft.Jet.OLEDB.4.0;Data Source=' + Destination + ';Jet OLEDB:Engine Type=5');
end;

procedure CompactDatabase(const MdbFileName: string;
  ADOConnection: TADOConnection=nil;
  const ReopenConnection: Boolean=True);
var
  LdbFileName, TempFileName: string;
  FailCount: Integer;
  FileHandle: Integer;
begin
  TempFileName := ChangeFileExt(MdbFileName, '.temp.mdb');
  if Assigned(ADOConnection) then
  begin
    // force the database engine to write data to disk, releasing locks on memory
    JroRefreshCache(ADOConnection);
    // close the connection - this will also close all associated datasets
    ADOConnection.Close;
  end;
  // ADOConnection.Close SHOULD delete the ldb
  // force delete of ldb lock file just in case if we don't have an active ADOConnection
  LdbFileName := ChangeFileExt(MdbFileName, '.ldb');
  if FileExists(LdbFileName) then
    DeleteFile(LdbFileName); // could fail because data is still locked - we ignore this
  // delete temp file if any
  if FileExists(TempFileName) then
    if not DeleteFile(TempFileName) then
       RaiseLastOSError;
  // try to open for exclusive use
  FailCount := 0;
  repeat
    FileHandle := FileOpen(MdbFileName, fmShareExclusive);
    try
      if FileHandle = -1 then // error
      begin 
        Inc(FailCount);
        Sleep(100); // give the database engine time to close completely and unlock
      end
      else
      begin
        FailCount := 0;
        Break; // success
      end;
    finally
      FileClose(FileHandle);
    end;
  until FailCount = 10; // maximum 1 second of attempts      
  if FailCount <> 0 then // file is probably locked by another user/process        
    raise Exception.Create(Format('Error opening %s for exclusive use.', [MdbFileName]));
  // compact the db
  JroCompactDatabase(MdbFileName, TempFileName);
  // copy temp file to original mdb and delete temp file on success
  if Windows.CopyFile(PChar(TempFileName), PChar(MdbFileName), False) then
    DeleteFile(TempFileName)
  else
    RaiseLastOSError;
  // reopen ADOConnection
  if Assigned(ADOConnection) and ReopenConnection then
    ADOConnection.Open;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  CompactDatabase('F:\Projects\DB\mydb.mdb', ADOConnection1, True);
  // reopen DataSets
  ADODataSet1.Open;
end;

<小时/>

确保您的 TADOConnection 在 IDE 中未设置为 Connected(设计模式)。
因为如果存在，则存在到数据库的另一个事件连接。