TDBReader

dataset.first
while not dataset.eof do
begin
   --N行代码
   dataset.next;
end

讨厌上面的写法了,作个封装.

interface

uses
  System.SysUtils, System.Classes, Data.DB;

type
  IDBReader = interface
    ['{EC98E980-0044-4E7C-B583-B6341B7147E5}']
    function Next: Boolean;
    procedure Reset;
    function GetValue(name: string): TField;
    property Value[name: string]: TField read GetValue;
  end;

  TDBReader = class(TInterfacedObject, IDBReader)
  private
    FBeforeFirst: Boolean;
    FDataSet: TDataSet;
    function GetValue(name: string): TField;
  public
    constructor Create(ADataSet: TDataSet);
    destructor Destroy; override;
    function Next: Boolean;
    procedure Reset;
    property Value[name: string]: TField read GetValue;
  end;

implementation

{ TDBReader }

constructor TDBReader.Create(ADataSet: TDataSet);
begin
  inherited Create;
  FBeforeFirst := True;
  FDataSet := ADataSet;
  FDataSet.First;
end;

destructor TDBReader.Destroy;
begin
  FDataSet.Free;
  inherited;
end;

function TDBReader.GetValue(name: string): TField;
begin
  Result := FDataSet.FieldByName(name);
end;

function TDBReader.Next: Boolean;
begin
  if FBeforeFirst then
  begin
    FBeforeFirst := False;
    Result := not FDataSet.IsEmpty;
  end
  else
  begin
    FDataSet.Next;
    Result := not FDataSet.Eof;
  end;
end;

procedure TDBReader.Reset;
begin
  FDataSet.First;
  FBeforeFirst := True;
end;

end.

 封装后代码少敲两行代码

procedure TForm1.Button1Click(Sender: TObject);
var
  R: TDBReader;
begin
  R := ExecQuery('SELECT * FROM PUB_BMK');
  while R.Next do
    ListBox1.Items.Add(R.Value['bm'].AsString);
  R.Free;
end;

 对比下面的,代码行数少4行.

procedure TForm1.Button2Click(Sender: TObject);
var
  ds: TDataSet;
begin
  ds := ExecQuery2('select * from aaa');
  ds.First;
  while not ds.Eof do
  begin
    ListBox1.Items.Add(ds.FieldByName('f').AsString);
    Next;
  end;
  ds.Free;
end;