delphi7环境下adodataset的一个讨论

idecl 2011-02-10 11:10:39





unit Unit1;



interface



uses

  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

  Dialogs, DB, ADODB, StdCtrls;



type

  TForm1 = class(TForm)

    Button1: TButton;

    ADODataSet1: TADODataSet;

    ADODataSet1a: TStringField;

    ADODataSet1b: TStringField;

    ADODataSet1c: TStringField;

    Button2: TButton;

    procedure Button1Click(Sender: TObject);

    procedure Button2Click(Sender: TObject);

    procedure FormCreate(Sender: TObject);

  private

    { Private declarations }

  public

    { Public declarations }

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



procedure TForm1.Button1Click(Sender: TObject);

var

  i :Integer;

begin

  ADODataSet1.Filtered := false;

 for i := 0 to 100 do

  adodataset1.InsertRecord([IntToStr(i),IntToStr(i),IntToStr(i)]);

end;



procedure TForm1.Button2Click(Sender: TObject);

begin

  ADODataSet1.Filter := 'a=' +quotedstr('111');

 ADODataSet1.Filtered := True;

  ShowMessage(IntToStr(ADODataSet1.RecordCount));

  //if (not ADODataSet1.Eof) and (not ADODataSet1.Bof) then

    if ADODataSet1.Locate('a','1',[]) then

       ShowMessage(ADODataSet1.fieldbyname('a').AsString);

end;



procedure TForm1.FormCreate(Sender: TObject);

begin

  ADODataSet1.CreateDataSet;

end;



end.

以上是一个简单的测试代码

1、Button2中过滤后没有记录时，再LOCATE一个存在的记录，就会报BOF或EOF为真的错误

2、将button2中的代码改成

ADODataSet1.Filter := 'a=' +quotedstr('1');
ADODataSet1.Filtered := True;
if ADODataSet1.Locate('a','0',[]) then
ShowMessage(ADODataSet1.fieldbyname('a').AsString);

会发现show出来的是‘1’。

3、将button2中的代码改成
ADODataSet1.Filter := 'a=' +quotedstr('0'); //第一条
ADODataSet1.Filtered := True;

if ADODataSet1.Locate('a','1',[]) then
ShowMessage(ADODataSet1.fieldbyname('a').AsString);
或
ADODataSet1.Filter := 'a=' +quotedstr('100');
ADODataSet1.Filtered := True;
if ADODataSet1.Locate('a','100',[]) then //最后一条
ShowMessage(ADODataSet1.fieldbyname('a').AsString);

会发现什么也不show

具体原因大家可以分析一下，提示一下：注意分析 TCustomADODataSet.LocateRecord 这个函数

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