使用for in 循环数据集

在DELPHI没有FOR IN的语法时,我们要使用如下代码枚举数据集中的每个内容:

cds.First;

while not cds.eof do begin

 ...

 cds.Next;

end;

最少要四句,而且字数有些多.如果程序中大量使用这个,代码看起来总是不舒服.

在DELPHI XE,可以利用XE对 FOR IN 扩展,建立新的扩展,使用起来好象有点动态语言的味道:

unit faDataSetEx;

interface

uses
  DB,ADODB,Variants,SysUtils,StrUtils,Controls,System.Types,Classes,DBClient;

type

  TFieldsEx = class helper for TFields
  private
    function GetFV (Index :String) :Variant;
    procedure SetFV (Index :String; const Value :Variant);
  public
    property FV[Index :String] :Variant read GetFV write SetFV; default;
  end;

  TDataSetEnumerator = class
  private
    FFirst   :boolean;
    FDataSet :TDataSet;
    function GetCurrent :TFields;
  public
    constructor Create (dataset :TDataSet);

    function MoveNext :boolean;
    property Current :TFields read GetCurrent;
  end;

  TDataSetEx = class helper for TDataSet
  public
    function GetEnumerator :TDataSetEnumerator;
  end;

implementation

{ TDataSetEx }

function TDataSetEx.GetEnumerator :TDataSetEnumerator;
begin
  Result := TDataSetEnumerator.Create (Self);
end;

{ TDataSetEnumerator }

constructor TDataSetEnumerator.Create (dataset :TDataSet);
begin
  FDataSet := dataset;

  FFirst := True;

end;

function TDataSetEnumerator.GetCurrent :TFields;
begin
  Result := FDataSet.Fields;
end;

function TDataSetEnumerator.MoveNext :boolean;
begin
  if FFirst then begin
    FFirst := False;
    FDataSet.First;
  end
  else
    FDataSet.Next;

  Result := not FDataSet.eof;
end;

{ TFieldsEx }

function TFieldsEx.GetFV (Index :String) :Variant;
begin
  Result := FieldByName (Index).Value;
end;

procedure TFieldsEx.SetFV (Index :String; const Value :Variant);
begin
  FieldByName (Index).Value := Value;
end;

end.

faDataSetEx

有了上面单元的代码,我们可以这样枚举数据集的每个行:

var
  d :TFields;
begin
  for d in cds1 do begin
    cds1.edit;
    d['a']:='abc';
    cds1.post;
  end;
end;

相当方便........