[转载] 学习TClientDataset的使用
[转载] 学习TClientDataset的使用 http://blog.csdn.net/onebigday/article/details/6275550
这个控件好像很好用，以前都是用TSimpledataset，现在突然想用一下它。要用它，好像比TSimpleDataset多几个控件，我是加了以下几个控件，TSQLConnection,TSQLQuery,TDataSetProvider,TClientDataset,TDataSource,TDBGrid。这几个控件中，TDBGrid的DataSource属性设为TDataSource，TDataSource的DataSet属性设为TClientDataset，TClientDataset的ProviderName属性设为TDataSetProvider，TDataSetProvider的Dataset属性设为TSQLQuery，TSQLQuery的SQLConnection属性设为TSQLConnection。
其中还要对TDataSetProvider设置一个属性，就是TDataSetProvider中的Options->poAllowCommandText这个属性设置为True，如果不设置为True的话，调用TClientDataset的Open时，会出现" commandtext changes are not allowed"的错误。以上设置完后，就可以用ClientDataSet1.CommantText := 'SELECT * FROM MYTABLE'（注意：SQL语句一定要大写，不然在调用ClientDataset1.ApplyUpdates时会出现“table or view does not exist”的错误）之类的语句设置SQL语句，然后用ClientDataSet1.Open来取得数据。在TDBGrid中修改了数据后就可以用ClientDataset1.ApplyUpdates(0)来把数据更新到数据库中了。
对于有二进制字段的，可以把TDataSetProvider->Options->poFetchBlobOnDemand设为True。这样程序一开始并不加载Blob字段的数据，如果用到了，TClientDataset会自动加载，对于我们程序员来说，是透明的，不需做额外的事，如正常一样访问TClientDataSet中的Blob字段就行了，要注意的是TClientDataSet的CommantText一定要有Select到Blob的SQL语句，而且，SQL语句一定要是大写的，不然也会出现“table or view does not exist”的错误。
完整的测试代码如下：
pas代码：
[delphi] view plaincopyprint?
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, DBXpress, FMTBcd, SqlExpr, StdCtrls, DB, DBClient, Provider,
Grids, DBGrids;
type
TForm1 = class(TForm)
DBGrid1: TDBGrid;
DataSource1: TDataSource;
DataSetProvider1: TDataSetProvider;
ClientDataSet1: TClientDataSet;
SQLConnection1: TSQLConnection;
Button1: TButton;
Button2: TButton;
SQLQuery1: TSQLQuery;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
ClientDataSet1.Close;
ClientDataSet1.CommandText := 'SELECT * FROM MYTABLE1'; //SQL语句一定要大写，不然在调用ClientDataset1.ApplyUpdates(0)时会出现“table or view does not exist”的错误
ClientDataSet1.Open;
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
ClientDataSet1.ApplyUpdates(0);
end;
end.
dfm代码如下：
[delphi] view plaincopyprint?
object Form1: TForm1
Left = 245
Top = 238
Width = 1142
Height = 656
Caption = 'Form1'
Color = clBtnFace
Font.Charset = DEFAULT_CHARSET
Font.Color = clWindowText
Font.Height = -11
Font.Name = 'MS Sans Serif'
Font.Style = []
OldCreateOrder = False
PixelsPerInch = 96
TextHeight = 13
object DBGrid1: TDBGrid
Left = 152
Top = 88
Width = 529
Height = 233
DataSource = DataSource1
TabOrder = 0
TitleFont.Charset = DEFAULT_CHARSET
TitleFont.Color = clWindowText
TitleFont.Height = -11
TitleFont.Name = 'MS Sans Serif'
TitleFont.Style = []
end
object Button1: TButton
Left = 528
Top = 32
Width = 75
Height = 25
Caption = 'Button1'
TabOrder = 1
OnClick = Button1Click
end
object Button2: TButton
Left = 704
Top = 40
Width = 75
Height = 25
Caption = 'Button2'
TabOrder = 2
OnClick = Button2Click
end
object DataSource1: TDataSource
DataSet = ClientDataSet1
Left = 160
Top = 24
end
object DataSetProvider1: TDataSetProvider
DataSet = SQLQuery1
Options = [poAllowCommandText]
Left = 288
Top = 24
end
object ClientDataSet1: TClientDataSet
Aggregates = <>
Params = <>
ProviderName = 'DataSetProvider1'
Left = 224
Top = 16
end
object SQLConnection1: TSQLConnection
ConnectionName = 'OracleConnection'
DriverName = 'Oracle'
GetDriverFunc = 'getSQLDriverORACLE'
LibraryName = 'dbexpora.dll'
LoginPrompt = False
Params.Strings = (
'DriverName=Oracle'
'DataBase=192.168.1.100'
'User_Name=qgtg'
'Password=qgtg'
'RowsetSize=20'
'BlobSize=-1'
'ErrorResourceFile='
'LocaleCode=0000'
'Oracle TransIsolation=ReadCommited'
'OS Authentication=False'
'Multiple Transaction=False'
'Trim Char=False')
VendorLib = 'oci.dll'
Left = 376
Top = 24
end
object SQLQuery1: TSQLQuery
MaxBlobSize = -1
Params = <>
SQLConnection = SQLConnection1
Left = 336
Top = 24
end
end
