delphi 编程技巧

				在Delphi中实现VFP6的查询速度 (2001年4月5日) 
				
				网友更新  分类:数据库   作者:tomye  推荐:tomye   阅读次数:284  
				(http://www.codesky.net)  
				
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				在Delphi中访问Foxpro的数据库效率非常低，一条简单的SQL都要检索半天。对于百万条记录
				的表BDE根本拖不动。笔者因为经常要处理这种庞大的数据表，所以在这上面花足了心思，终于
				探索出一种简单可靠的方法。
				首先，我们现用VFP6写一个类，这个类很简单，如下所示：
				Define Class mFoxEngine As Session OlePublic
				mSQLString='' 
				mRecCount=0
				mSpentCount=0
				
				Procedure InitEngine
				Set Collate to 'MACHINE'
				Set Talk off
				Set safe off
				Set dele off
				Set Excl off
				set cent on
				set date to ansi
				Close Data
				EndProc
				
				Function RunSQL
				lStart=Seco()
				pSQLString=This.mSQLString
				&pSQLString
				This.mRecCount=_Tally
				Close Data
				This.mSpentCount=Seco()-lStart
				if _Tally=0
				Retu .f.
				else
				Retu .t.
				Endif
				EndFunc 
				
				EndDefine
				
				把此类编译成支持多线程的COM内进程组件。（VFP6必须已经上了Pack4补丁）
				注册该COM的DLL。
				在Delphi中可以使用该组件了。简单的用法为：
				var myObject:Variant;
				begin
				myObject:=CreateOleObject('FoxEngine.mFoxEngine');
				myObject.InitEngine; //初使化引擎
				myObject.mSQLString:='Sele * from XXX into dbf XXX'; //随你怎么用，只要VFP支持的SQL和函数就可，也是我们想要的。
				if not VarIsEmpty(myObject) then myObject:=null; //释放。可选因为Delphi会自动释放
				end;
				
				上述做法可以很好的和VFP6的引擎结合，达到意想不到的效果。
				笔者同时把此VFP6引擎做成了一个控件，源码如下：
				unit FoxQuery;
				
				interface
				
				uses
				Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
				Db,ComObj;
				
				type
				TFoxQuery = class(TDataSet)
				private
				{ Private declarations }
				FSQLString:String;
				FActive:Boolean;
				FFoxObject:Variant;
				FSQL:TStrings;
				FRecCount:Integer;
				FVersion:String;
				FSpentCount:Integer;
				
				Procedure FoxSetActive(Value:Boolean);
				Procedure SetSQL(Value:TStrings);
				Procedure Execute;
				
				protected
				{ Protected declarations }
				public
				{ Public declarations }
				Constructor Create(AOwner: TComponent); override;
				Destructor Destroy; override;
				Procedure ClearSQL;
				
				published
				{ Published declarations }
				Property Active:Boolean Read FActive Write FoxSetActive;
				Property SQL:TStrings Read FSQL Write SetSQL;
				Property RecCount:Integer Read FRecCount;
				Property SpentCount:Integer Read FSpentCount;
				Property SQLString:string Read FSQLString Write FSQLString;
				Property Version:String Read FVersion Write FVersion;
				end;
				
				procedure Register;
				
				implementation
				{$R *.res}
				Procedure TFoxQuery.FoxSetActive(Value:Boolean);
				begin
				if Value then
				begin
				if FSQLString='' then
				begin
				MessageBox(0,'SQL Command is empty!','Error',mb_iconstop);
				FActive:=false;
				end else begin
				FActive:=true;
				Execute;
				end;
				end;
				end;{}
				
				Procedure TFoxQuery.ClearSQL;
				begin
				FSQLString:='';
				end;
				
				Procedure TFoxQuery.SetSQL(Value:TStrings);
				Var i:integer;
				Begin
				if SQL.Text  Value.Text then
				begin
				SQL.BeginUpdate;
				try
				SQL.Assign(Value);
				finally
				SQL.EndUpdate;
				end;
				end;
				FSQLString:='';
				if SQL.Count0 then
				begin
				for i:=0 to FSQL.Count-1 do
				begin
				FSQLString:=FSQLString+FSQL.Strings[i];
				end;
				end;
				end;
				
				Procedure TFoxQuery.Execute;
				begin
				FFoxObject.mSQLString:=FSQLString;
				FFoxObject.RunSQL;
				FRecCount:=FFoxObject.mRecCount;
				FSpentCount:=FFoxObject.mSpentCount;
				end;
				
				
				Constructor TFoxQuery.Create(AOwner: TComponent);
				begin
				inherited Create(AOwner);
				FFoxObject:=CreateOleObject('FoxEngine.mFoxEngine');
				FFoxObject.InitEngine;
				FSQL:=TStringList.Create;
				FVersion:='Version 1.0.0';
				end;{}
				
				Destructor TFoxQuery.Destroy;
				begin
				inherited Destroy;
				if not VarIsEmpty(FFoxObject) then FFoxObject:=Null;
				FSQL.Free;
				end;
				
				procedure Register;
				begin
				RegisterComponents('Data Access', [TFoxQuery]);
				end;
				
				end.
				
				以上内容在Delphi5和VFP6(Pack4)中试用通过。
				如想导论此技术请联系笔者：
				Mail: tom_yea@163.com
				HomePage: http://www.tomye.com