delphi三层中间件 框架【首页】

在Delphi中创建三层结构的应用程序通常涉及到数据访问层（DAL）、业务逻辑层（BLL）和用户界面层（UI）。以下是一个简单的例子，展示了如何在Delphi中创建一个简单的三层架构的应用程序。

数据访问层（DAL）:

unit DataAccessLayer;
 
interface
 
uses
  DBXpress, SysUtils;
 
type
  TDataAccessLayer = class
  private
    FSQLConnection: TSQLConnection;
  public
    constructor Create;
    destructor Destroy; override;
    function ExecuteQuery(const SQL: string): TDataSet;
  end;
 
implementation
 
constructor TDataAccessLayer.Create;
begin
  inherited Create;
  FSQLConnection := TSQLConnection.Create(nil);
  FSQLConnection.DriverName := 'DataSnap';
  FSQLConnection.Params.Values['HostName'] := 'localhost';
  FSQLConnection.Params.Values['DataPacketSize'] := '256';
  FSQLConnection.Params.Values['CommunicationProtocol'] := 'tcp/ip';
  FSQLConnection.Params.Values['DatasnapContext'] := 'false';
end;
 
destructor TDataAccessLayer.Destroy;
begin
  FSQLConnection.Free;
  inherited Destroy;
end;
 
function TDataAccessLayer.ExecuteQuery(const SQL: string): TDataSet;
var
  Q: TSQLQuery;
begin
  Q := TSQLQuery.Create(nil);
  try
    Q.SQLConnection := FSQLConnection;
    Q.SQL.Text := SQL;
    Q.Open;
    Result := Q;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end;
 
end.

业务逻辑层（BLL）:

unit BusinessLogicLayer;
 
interface
 
uses
  DataAccessLayer;
 
type
  TBusinessLogicLayer = class
  private
    FDataAccessLayer: TDataAccessLayer;
  public
    constructor Create;
    destructor Destroy; override;
    function GetUsers: TDataSet;
  end;
 
implementation
 
constructor TBusinessLogicLayer.Create;
begin
  inherited Create;
  FDataAccessLayer := TDataAccessLayer.Create;
end;
 
destructor TBusinessLogicLayer.Destroy;
begin
  FDataAccessLayer.Free;
  inherited Destroy;
end;
 
function TBusinessLogicLayer.GetUsers: TDataSet;
begin
  Result := FDataAccessLayer.ExecuteQuery('SELECT * FROM Users');
end;
 
end.

用户界面层（UI）:

unit MainForm;
 
interface
 
uses
  Vcl.Forms, Vcl.Grids, Vcl.DBGrids, Data.DB, DataAccessLayer, BusinessLogicLayer, Vcl.StdCtrls;
 
type
  TFormMain = class(TForm)
    DBGrid1: TDBGrid;
    DataSource1: TDataSource;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    FBusinessLogicLayer: TBusinessLogicLayer;
    FDataSet: TDataSet;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  end;
 
var
  FormMain: TFormMain;
 
impl