DataSnap数据库连接池，数据集对象池的应用

    传统的应用服务器的开发往往是在ServerMethods单元中拖放一堆TDataSet, TDaTaSetProvider控件，这是一个最简单粗暴的开发方向，往往会造成服务端程序文件的臃肿、服务运行期间内存资源消耗过大的问题。因此这种往应用服务器中拖放一堆TDataSet, TDaTaSetProvider控件的做法，非常的笨拙。

    当然了，如果我们的系统采用的是以短连接的方式的话，那就可以每次直接TDataSet.Create(nil);然后Free;但是这种方法对服务器的开销很大，因为每执行一个服务都需要重复开辟内存空间，销毁内存空间等。

    为此，我们可以通过使用对象池方法来改进之。

一、数据库连接池：TConnection对象池

unit DSServerContainer;

interface

uses
  SysUtils, Classes,
  DSTCPServerTransport,
  DSServer, DSCommonServer, DSAuth, DB, ADODB, Generics.Collections, DSService,
  DBXDataSnap, DBXCommon, DSHTTPLayer, DBXinterbase, Forms;

type
  TServerContainer1 = class(TDataModule)
    DSServer1: TDSServer;
    DSTCPServerTransport1: TDSTCPServerTransport;
    DSServerClass1: TDSServerClass;
    procedure DSServerClass1GetClass(DSServerClass: TDSServerClass;
      var PersistentClass: TPersistentClass);
    procedure DataModuleCreate(Sender: TObject);
    procedure DSServer1Disconnect(DSConnectEventObject: TDSConnectEventObject);
  private
    { Private declarations }
    ListofConnection : TDictionary<Integer,TadoConnection>;
  public
    function getConnection : TAdoConnection;
  end;

var
  ServerContainer1: TServerContainer1;

implementation

uses Windows, ServerMethodsUnit1,uConst;

{$R *.dfm}

procedure TServerContainer1.DataModuleCreate(Sender: TObject);
begin
  ListofConnection := TDictionary<Integer, TadoConnection>.Create;
end;

procedure TServerContainer1.DSServer1Disconnect(
  DSConnectEventObject: TDSConnectEventObject);
begin
  if getConnection <> nil then
     getConnection.Close;
end;

procedure TServerContainer1.DSServerClass1GetClass(
  DSServerClass: TDSServerClass; var PersistentClass: TPersistentClass);
begin
  PersistentClass := ServerMethodsUnit1.TServerMethods1;
end;

function TServerContainer1.getConnection: TAdoConnection;
var
  dbconn : TAdoConnection;
begin
  if ListofConnection.ContainsKey(TDSSessionManager.GetThreadSession.Id) then
     Result := ListofConnection[TDSSessionManager.GetThreadSession.Id]
  else
  begin
    if ListofConnection.Count <= g_MaxPoolSize then
    begin
      dbconn := TadoConnection.Create(Self);
      dbconn.Name := 'con'+ IntToStr(TDSSessionManager.GetThreadSession.Id);
      dbconn.LoginPrompt := false;
      dbconn.ConnectionString := 'FILE NAME=' + extractfilepath(application.ExeName) + 'connect.udl';
      ListofConnection.Add(TDSSessionManager.GetThreadSession.Id, dbconn);
      Result := dbconn;
    end;
  end;
end;

end.

二、数据集对象池：TDataSet和TDataSetProvider的池化

unit ServerMethodsUnit1;

interface

uses
  SysUtils, Classes, DSServer, DB, Generics.Collections, DSService, Provider,
  ADODB;

type
  TServerMethods1 = class(TDSServerModule)
    procedure DSServerModuleCreate(Sender: TObject);
  private
    { Private declarations }
    ListofQuery : TDictionary<Integer,TAdoQuery>;
    ListofProvider : TDictionary<Integer,TDatasetProvider>;
    function _GetQuery(sql: string; exeNo: Integer) : TAdoquery;
    function _GetPrv(sql: string; exeNo: Integer) : TDatasetProvider;
  public
    { Public declarations }
    function GetProviderName(sql: string; exeNo: Integer): string;
  end;

implementation

{$R *.dfm}

uses StrUtils, DSServerContainer, uConst;

procedure TServerMethods1.DSServerModuleCreate(Sender: TObject);
begin
  Listofquery := TDictionary<Integer, Tadoquery>.Create;
  Listofprovider := TDictionary<Integer, Tdatasetprovider>.Create;
end;

function TServerMethods1._GetPrv(sql: string; exeNo: Integer): TDatasetProvider;
var
  dbprv : Tdatasetprovider;
begin
  if ListofProvider.ContainsKey(exeNo) then
     Result := ListofProvider[exeNo]
  else
  begin
    if ListofProvider.Count <= g_MaxPoolSize then
    begin
      dbprv := TDataSetProvider.Create(Self);
      dbprv.Name := 'dsp'+ IntToStr(exeNo);
      dbprv.DataSet := _GetQuery(sql, exeNo);
      ListofProvider.Add(exeNo, dbprv);
      Result := dbprv;
    end;
  end;
end;

function TServerMethods1._GetQuery(sql: string; exeNo: Integer): TAdoQuery;
var
  qry : TADOQuery;
begin
  if Listofquery.ContainsKey(exeNo) then
     Result := ListofQuery[exeNo]
  else
  begin
    if ListofQuery.Count <= g_MaxPoolSize then
    begin
      qry := TADOQuery.Create(Self);
      with qry do
      begin
        Connection := ServerContainer1.getConnection;
        Name := 'qry'+ IntToStr(exeNo);
        close;
        sql.Clear;
        sql.Text := sql;
        open;
      end;
      ListofQuery.Add(exeNo, qry);
      Result := qry;
    end;
  end;
end;

function TServerMethods1.GetProviderName(sql: string; exeNo: Integer): string;
begin
  Result := _GetPrv(sql, exeNo).Name;
end;

end.