TClientDataSet[12]: 查找

方法有:
1、Locate: 根据字段列表和对应的字段值查找并定位, 找到返回 True.
2、Lookup: 根据字段列表和对应的字段值查找, 返回需要的字段值.
3、SetKey、GotoKey 或 SetKey、GotoNearest: 根据索引字段的值查找, 先切换状态再根据条件定位.
4、FindKey 或 FindNearest: 根据索引字段的值查找.

其中的 GotoNearest、FindNearest 在找不到的情况下会定位到近似值.

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测试代码:

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//准备: 窗体上放一个 ClientDataSet1 和六个 Button

{ 准备测试数据 }
procedure TForm1.FormCreate(Sender: TObject);
begin
  with ClientDataSet1 do begin
    FieldDefs.Add('ID', ftInteger);
    FieldDefs.Add('Name', ftString, 6);
    FieldDefs.Add('Age', ftWord);
    CreateDataSet;
    AppendRecord([1, '赵AB', 11]);
    AppendRecord([2, '钱AB', 22]);
    AppendRecord([3, '孙AB', 33]);
    AppendRecord([4, '李AB', 44]);
    AppendRecord([5, '赵ab', 55]);
    AppendRecord([6, '钱ab', 66]);
    AppendRecord([7, '孙ab', 77]);
    AppendRecord([8, '李ab', 88]);
  end;
end;

{ Locate 测试 }
procedure TForm1.Button1Click(Sender: TObject);
begin
  if ClientDataSet1.Locate('Name', '赵ab', []) then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 55 }

  if ClientDataSet1.Locate('Name', '赵ab', [loCaseInsensitive]) then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 11 }

  if ClientDataSet1.Locate('Name', '钱a', [loPartialKey]) then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 66 }

  if ClientDataSet1.Locate('Name', '钱a', [loCaseInsensitive,loPartialKey]) then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 22 }

  if ClientDataSet1.Locate('Name;Age', VarArrayOf(['钱ab',66]), []) then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 66 }
end;

{ Lookup 测试 }
procedure TForm1.Button2Click(Sender: TObject);
var
  R: Variant;
  i: Integer;
begin
  R := ClientDataSet1.Lookup('Name', '钱AB', 'Age');
  if not VarIsNull(R) then ShowMessage(R); { 22 }

  R := ClientDataSet1.Lookup('Name;Age', VarArrayOf(['钱ab',66]), 'Age');
  if not VarIsNull(R) then ShowMessage(R); { 66 }

  R := ClientDataSet1.Lookup('ID', 6, 'Name;Age');
  if VarIsArray(R) then
    for i := VarArrayLowBound(R, 1) to VarArrayHighBound(R, 1) do
      ShowMessage(R[i]); { 钱ab / 66}
end;

{ SetKey、GotoKey 测试 }
procedure TForm1.Button3Click(Sender: TObject);
begin
  ClientDataSet1.IndexFieldNames := 'Name';
  ClientDataSet1.SetKey;
  ClientDataSet1.FieldValues['Name'] := '钱ab';
  if ClientDataSet1.GotoKey then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 66 }
end;

{ SetKey、GotoNearest 测试 }
procedure TForm1.Button4Click(Sender: TObject);
begin
  ClientDataSet1.IndexFieldNames := 'Name';
  ClientDataSet1.SetKey;
  ClientDataSet1.FieldValues['Name'] := '孙';
  ClientDataSet1.GotoNearest;
  ShowMessage(ClientDataSet1.FieldValues['Age']); { 77 }
end;

{ FindKey 测试 }
procedure TForm1.Button5Click(Sender: TObject);
begin
  ClientDataSet1.IndexFieldNames := 'Name; Age';

  if ClientDataSet1.FindKey(['赵ab']) then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 55 }

  if ClientDataSet1.FindKey(['赵AB', 11]) then
    ShowMessage(ClientDataSet1.FieldValues['Age']); { 11 }
end;

{ FindNearest 测试 }
procedure TForm1.Button6Click(Sender: TObject);
begin
  ClientDataSet1.IndexFieldNames := 'Name';
  ClientDataSet1.FindNearest(['赵']);
  ShowMessage(ClientDataSet1.FieldValues['Age']); { 55 }
end;