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TManagedDataSet和DataSetPool的实现_Delphi

Delphi 搞代码 3年前 (2018-08-09) 247次浏览 已收录 0个评论

         Delphi中使用最多的大概是AdoExpress组件,这是Borland封装了Microsoft的Ado的东东,使用频率最多的TAdoDataSet对应了Ado原生的RecordSet,在功能上做了一些增强,但用法基本一致,用多了就感觉TAdoDataSet还有扩充和改造的地方。

         由于代码中使用了很多的TAdoDataSet控件,创建和释放对象非常频繁,而且每次创建后都要设置很多基本相同的属性,颇为麻烦。于是想到可以实现一个记录集池,每次当需要一个记录集时,从这个池中得到一个空闲且符合要求的(只读或可读写),用完了就被池回收,如果池中记录集不够,就自动生成新的记录集对象。

         首先要做的是改造TAdoDataSet,我写了一个TManagedDataSet,继承自TAdoDataSet,可以自己知道自己是被人使用还是空闲(通过IsUsed()),重写了Free(),把本来释放的动作改为仅是把自己设置为空闲,并清除状态(Session)信息,并可以通过Source()返回一个指向自己的TDataSource对象。

         有了这些基础后,就可以很快的构建TDataSetPool类了,这个类仅是保存可用的TManagedDataSet对象,通过GetDataSet(WantType : TManagedDataSetType)返回一个空闲的数据集对象,如果池中没有空闲的,就新建一个返回。TManagedDataSetType是枚举类,标识只读数据集和读写数据集(只读数据集可通过优化CursorType和LockType来加快读数据速度)。

         下面的代码是直接从我做的一个项目的源文件中Copy出来的,有些乱,仅做参考。

http://www.gaodaima.com/?p=66041TManagedDataSet和DataSetPool的实现_Delphi

unit ManagedDataSet;

interface

uses AdoDb, CommonDm, SysUtils, DB, dbgrids, ComObj, classes, contnrs;

type

         TManagedDataSetType = (ReadOnly, Editable); // 猅羭摸

    TXlsExpAdapter = class

        private

           _sXlsCaption : string;

            _sXlsFileName : string;

            _bOverwriteExistFile : Boolean;

                            _asFieldName : TStringList;

            _asXlsTitle : TStringList;

            _aDataType : TObjectList;

            function GetDataType(const iniIndex : Integer) : TDataType;

            function GetFieldName(const iniIndex : Integer) : string;

            function GetXlsTitle(const iniIndex : Integer) : string;

        public

           constructor Create();

            destructor Destroy();

           property XlsCaption : string read _sXlsCaption Write _sXlsCaption;

            property XlsFileName : string read _sXlsFileName Write _sXlsFileName;

            property OverWriteExistFile : Boolean read _bOverwriteExistFile Write _bOverwriteExistFile;

                            procedure AddField(const insFieldName, insCaption : string; const intype : TDataType = ftUnKnown);

            procedure GetInfoFromDBGrid(const ingrid : TDBGrid);

            property DataType[const iniIndex : Integer] : TDataType read GetDataType;

            property FieldName[const iniIndex : Integer] : string read GetFieldName;

            property XlsTitle[const iniIndex : Integer] : string read GetXlsTitle;

            function Count() : Integer;

    end;

    TManagedDataSet = class(TAdoDataSet)

                   private

            _source : TDataSource;

            _type : TManagedDataSetType;

            _bUsed : Boolean;

            procedure SetDataSetType(const intype : TManagedDataSetType);

            function GetDataSource() : TDataSource;

        public

           constructor Create(const intype : TManagedDataSetType = Editable);

            destructor Destroy(); override;

                            procedure Use();

            procedure Free(); reintroduce; // 滦籠摸Freeぃ穦睦龟ㄒ

            property DataSetType : TManagedDataSetType read _type Write SetDataSetType;

            property IsUsed : Boolean read _bUsed;

            property Source : TDataSource read GetDataSource;

            function ExportToXls(const inadapter : TXlsExpAdapter) : Boolean;

    end;

implementation

function TXlsExpAdapter.Count() : Integer;

begin

    Result := _asFieldName.Count;

end;

function TXlsExpAdapter.GetXlsTitle(const iniIndex : Integer) : string;

begin

         if (iniIndex >= 0) and (iniIndex <= _aDataType.Count-1) then

    begin

    Result := _asXlsTitle[iniIndex];

    end;

end;

function TXlsExpAdapter.GetFieldName(const iniIndex : Integer) : string;

begin

         if (iniIndex >= 0) and (iniIndex <= _aDataType.Count-1) then

    begin

    Result := _asFieldName[iniIndex];

    end;

end;

function TXlsExpAdapter.GetDataType(const iniIndex : Integer) : TDataType;

begin

    if (iniIndex >= 0) and (iniIndex <= _aDataType.Count-1) then

    begin

        Result := TDataType(_aDataType[iniIndex]);

    end;

end;

procedure TXlsExpAdapter.GetInfoFromDBGrid(const ingrid : TDBGrid);

var

         i, j : Integer;

    dt : TDataType;

begin

         for i := 0 to ingrid.Columns.Count-1 do

    begin

                   if ingrid.Columns[i].Visible then

        begin

           dt := ftUnknown;

           for j := 0 to ingrid.FieldCount-1 do

            begin

                if ingrid.Columns[i].FieldName = ingrid.Fields[j].FieldName then

                begin

                    dt := ingrid.Fields[j].DataType;

                    Break;

                end;

            end;

            Self.AddField(ingrid.Columns[i].FieldName, ingrid.Columns[i].Title.Caption, dt);

        end;

    end;   

end;

procedure TXlsExpAdapter.AddField(const insFieldName, insCaption : string; const intype : TDataType = ftUnKnown);

var

         iIndex : Integer;

begin

         iIndex := _asFieldName.IndexOf(insFieldName);

    if iIndex = -1 then

    begin

        _asFieldName.Add(insFieldName);

        _asXlsTitle.Add(insCaption);

        _aDataType.Add(TObject(intype));

    end

    else begin

        _asFieldName[iIndex] := insFieldName;

        _asXlsTitle[iIndex] := insCaption;

        _aDataType[iIndex] := TObject(intype);

    end;

end;

constructor TXlsExpAdapter.Create();

begin

         _asFieldName := TStringList.Create();

    _asXlsTitle := TStringList.Create();

    _aDataType := TObjectList.Create();

end;

destructor TXlsExpAdapter.Destroy();

begin

end;

function TManagedDataSet.ExportToXls(const inadapter : TXlsExpAdapter) : Boolean;

var

         excelobj : OleVariant;

    i : Integer;

begin

         Result := False;

    

         if not Self.Active then

        Exit;

         try

    excelobj := CreateOleObject(‘Excel.Application’);

        excelobj.WorkBooks.Add;

    except

    Exit;

    end;

    if FileExists(inadapter.XlsFileName) and inadapter.OverWriteExistFile then

    begin

        DeleteFile(PChar(inadapter.XlsFileName));

    end

    else begin

        excelobj.Quit;

        Exit;

    end;

    for i := 0 to inadapter.Count-1 do

    begin

                   

    end;

end;

constructor TManagedDataSet.Create(const intype : TManagedDataSetType = Editable);

begin

         inherited Create(nil);

         Self.Connection := DmCommon.Cnn;

    Self.CursorLocation := clUseClient;

    Self.Prepared := True;

    Self.CacheSize := 1000;

    if intype = ReadOnly then

    begin

    Self.CursorType := ctOpenForwardOnly;

    Self.LockType := ltReadOnly;

    end

    else if intype = Editable then

    begin

        Self.CursorType := ctStatic;

    Self.LockType := ltOptimistic;

    end;

    _type := intype;

    _bUsed := False;

end;

destructor TManagedDataSet.Destroy();

begin

         if Self.Active then

    begin

             Self.Close;

    end;

    if Assigned(_source) then

    begin

             FreeAndNil(_source);

    end;

    inherited Destroy();

end;

procedure TManagedDataSet.Use();

begin

    if _bUsed then

    begin

        raise Exception.Create(‘Cannot get a used managed dataset !’);

    end;

    _bUsed := True;

end;

procedure TManagedDataSet.Free();

begin

         if Self.Active then

    begin

    Self.Close;

    end;

    Self.CommandText := ”;

    Self.Parameters.Clear; // 睲埃把计

    Self.MasterFields := ”; // 睲埃琿

    Self.DataSource := nil;

    Self.ExecuteOptions := []; // 睲埃磅︽匡兜

    _bUsed := False;

end;

procedure TManagedDataSet.SetDataSetType(const intype : TManagedDataSetType);

begin

    if intype = _type then

    Exit;

    if intype = ReadOnly then

    begin

    Self.CursorType := ctOpenForwardOnly;

    Self.LockType := ltReadOnly;

    end

    else if intype = Editable then

    begin

        Self.CursorType := ctStatic;

    Self.LockType := ltOptimistic;

    end;

end;

function TManagedDataSet.GetDataSource() : TDataSource;

begin

         if not Assigned(_source) then

    begin

             _source := TDataSource.Create(nil);

    _source.AutoEdit := False;

             _source.DataSet := Self;

    end;

    Result := _source;

end;

end.

unit DataSetPool; // 癘魁栋GlobalVarい承セ摸Ы龟ㄒ跑秖

interface

uses ManagedDataSet, Contnrs, SysUtils, AdoDb, Db, CommonDm;

type

         TDataSetPool = class

                   private

           _ads : TObjectList;

            function GetCount() : Integer;

        public

           constructor Create(const ini : Integer = 10);

            destructor Destroy(); override;

            property Count : Integer read GetCount;

            function GetDataSet(const intype : TManagedDataSetType = Editable) : TManagedDataSet;

            function GetAdoCommand() : TAdoCommand; // 度TAdoCommand睦パ秸ノ璽砫

    end;

implementation

constructor TDataSetPool.Create(const ini : Integer = 10);

begin

         _ads := TObjectList.Create;

end;

destructor TDataSetPool.Destroy();

begin

    FreeAndNil(_ads);

end;

function TDataSetPool.GetCount() : Integer;

begin

         Result := _ads.Count;

end;

function TDataSetPool.GetDataSet(const intype : TManagedDataSetType = Editable) : TManagedDataSet;

var

         i : Integer;

begin

         Result := nil;

         for i := 0  to _ads.Count-1 do

    begin

                   if (not TManagedDataSet(_ads[i]).IsUsed) and (TManagedDataSet(_ads[i]).DataSetType = intype) then

        begin

            Result := TManagedDataSet(_ads[i]);

            Result.Use;

            break;

        end;

    end;

    if Result = nil then

    begin

                   _ads.Add(TManagedDataSet.Create(intype));

        Result := TManagedDataSet(_ads[_ads.Count-1]);

        Result.Use;

    end;

end;

function TDataSetPool.GetAdoCommand() : TAdoCommand;

begin

         Result := TADOCommand.Create(nil);

    Result.Connection := DmCommon.Cnn;

end;

end.

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